CONTRAINDICATIONS / PRECAUTIONS
Glycerin hypersensitivity
Levothyroxine is contraindicated in any patient with a known hypersensitivity to levothyroxine or any of its excipients; however, there is no well-documented evidence in the literature of true allergic or idiosyncratic reactions to thyroid hormone. Hypersensitivity reactions to inactive ingredients have occurred in patients treated with thyroid hormone products. Levothyroxine oral capsule and oral solution are contraindicated in any patient with a known (glycerol) glycerin hypersensitivity. Levothyroxine injection and tablets are synthetically derived and may be used in patients allergic to desiccated thyroid or thyroid extract derived from pork or beef.
Adrenal insufficiency
Levothyroxine is contraindicated for use in patients with diagnosed but untreated adrenal insufficiency. Initiation of thyroid hormone therapy prior to initiating glucocorticoid therapy may precipitate an acute adrenal crisis in patients with adrenal insufficiency due to an increase in the body's demand for adrenal hormones. Treat patients with adrenal insufficiency with replacement glucocorticoids prior to initiating treatment with levothyroxine.
Hypopituitarism
Serum TSH is not a reliable measure of levothyroxine dose adequacy in patients with secondary (hypopituitarism) hypothyroidism or tertiary (hypothalamic) hypothyroidism and should not be used to monitor therapy. An inappropriate TSH may be seen if hypothyroidism is caused by TSH deficiency (e.g., secondary hypothyroidism in patients with panhypopituitarism), and the TSH will not normalize with thyroid treatment. Use the serum free-T4 level to monitor for adequacy of therapy in this patient population.
Acute myocardial infarction, angina, cardiac arrhythmias, cardiac disease, coronary artery disease, heart failure, hypertension, myocardial infarction, surgery
Many authorities recommend lower initial dosages and slower titration of thyroid hormones in patients with cardiac disease and coronary artery disease (CAD). Thyroid hormones such as levothyroxine should be used with great caution in patients where the integrity of the cardiovascular system is suspect. All levothyroxine dosage formulations are cardiostimulatory and should be used with great caution in patients with angina pectoris, uncontrolled hypertension, cardiac arrhythmias, CAD, a previous history of acute myocardial infarction, or current acute myocardial infarction. If adverse cardiac symptoms develop or worsen during treatment, reduce or withhold levothyroxine and cautiously restart at a lower dose. Over-treatment with thyroid hormones may cause cardiac stimulation and lead to increased heart rate, cardiac wall thickening, and increased cardiac contractility, which may precipitate angina or cardiac arrhythmias. Concomitant administration of levothyroxine with vasopressors or sympathomimetic agents may precipitate coronary insufficiency and associated symptoms, particularly in myxedematous patients or those with CAD. Fluid therapy should be administered with great care to prevent cardiac decompensation. In patients with compromised cardiac function, use thyroid hormones in conjunction with careful cardiac monitoring. A lower starting dose is recommended in adult and pediatric patients at risk for heart failure or sensitive to thyroid stimulation. Careful monitoring is also recommended during surgery, as some anesthetic agents may induce changes in heart rate or blood pressure when administered with thyroid hormones.
Diabetes mellitus
Levothyroxine therapy can worsen glycemic control in patients with diabetes mellitus, and result in increased antidiabetic agent or insulin requirements. The effects seen are poorly understood and depend upon a variety of factors such as dose and type of thyroid preparations and endocrine status of the patient. Blood glucose should be monitored closely during concomitant therapy, particularly during initiation, dose adjustments, or discontinuation of therapy.
Obesity treatment
Levothyroxine should not be used for obesity treatment or weight loss. In euthyroid patients, thyroid hormone doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious manifestations of toxicity and hyperthyroidism, especially if used with anorexic agents such as the sympathomimetic amines.
Hyponatremia, hypothermia, myxedema, water intoxication
Patients with myxedema coma require immediate and intensive treatment. Myxedema coma is a life-threatening emergency characterized by poor circulation and hypometabolism and may result in unpredictable absorption of oral thyroid hormone from the gastrointestinal tract. Initial thyroid hormone replacement for myxedema coma should be given intravenously. The use of oral thyroid hormone drug products is not recommended.[60310] [53562] Although patients with myxedema coma often suffer from hypothermia, artificial rewarming is contraindicated. Peripheral vasodilation produced by artificial external heat further decreases circulation to vital internal organs and may increase shock if present. Administration of levothyroxine may restore normal body temperature within 24 to 48 hours if heat loss is prevented by keeping the patient covered with blankets in a warm room. Patients with myxedema coma show increased sensitivity to thyroid agents; initiate therapy with low doses of intravenous levothyroxine and increase gradually. Simultaneous administration of glucocorticoids is required for these patients. Patients with pituitary myxedema should receive such adrenocortical hormone replacement therapy at or before the start of thyroid hormone treatment to prevent acute adrenocortical insufficiency and shock. Hyponatremia is frequently present in myxedema coma, but usually resolves without specific therapy as the metabolic status of the patient improves with thyroid treatment. Use great care with fluid therapy to prevent cardiac decompensation; some patients with myxedema have inappropriate secretion of ADH and are susceptible to water intoxication. In some patients, respiratory depression has been a significant factor in the development or persistence of the comatose state. Decreased oxygen saturation and elevated CO2 levels respond quickly to artificial respiration.[60310]
Osteopenia
Long-term use of levothyroxine has been associated with decreased bone mineral density with increased bone resorption, particularly in postmenopausal females on greater than replacement doses or in women receiving suppressive doses. The increased bone resorption may be associated with increased serum levels and urinary excretion of calcium and phosphorous, elevations in bone alkaline phosphatase, and suppressed serum parathyroid hormone levels. Patients should be given the minimum dose necessary for desired clinical and biochemical response to limit risks for osteopenia.
Dysphagia
Levothyroxine capsules (Tirosint and others) are contraindicated for use in anyone unable to swallow a capsule, generally including pediatric patients less than 6 years of age and those patients with dysphagia. Do not cut or crush the capsules. Use caution when administering the Levoxyl brand of levothyroxine tablets to patients with dysphasia or other conditions that compromise the ability to swallow. Choking, gagging, tablets getting stuck in the throat, and dysphagia have been reported, mainly when the intact tablets were not taken with water. Counsel patients to take the tablet with water.
Geriatric
Caution should be used in geriatric patients since they may be more sensitive to the cardiac effects of thyroid replacement. In general, lower initial dosages and slower titration are recommended in elderly patients. Overall, thyroid hormone requirements in the elderly are typically 25% lower than in younger adults; individualize dosage. Atrial arrhythmias can occur in elderly patients. Atrial fibrillation is the most common of the arrhythmias observed with levothyroxine overtreatment in the elderly.[33700] [43942] [43952] [43943] [53562] [61764] According to the Beers Criteria, levothyroxine is the preferred replacement hormone versus other thyroid replacement medications; guidelines state levothyroxine is the agent of choice for most patients for hypothyroidism. [60310] The federal Omnibus Budget Reconciliation Act (OBRA) regulates medication use in residents of long-term care facilities (LTCFs); assessment of thyroid function (e.g., TSH, serum T4 or T3) should occur before initiating thyroid medication and periodically thereafter; reassess thyroid function if new signs and symptoms of hypothyroidism or hyperthyroidism develop. Initiate thyroid supplementation at low doses and increase gradually to avoid precipitating cardiac failure or adrenal crisis. Because there are many clinically significant medication interactions, re-evaluation of medication doses should occur as clinically indicated.
Pregnancy
Hypothyroidism that is diagnosed during pregnancy should be promptly treated. During pregnancy, thyroxine (T4) is thought to be crucial for fetal brain development, and guidelines recommend that levothyroxine be the preferred drug for the treatment of hypothyroidism in the pregnant patient.[60310] The clinical experience to date does not indicate any adverse fetal effect when thyroid hormones such as levothyroxine are administered during pregnancy. Thyroid replacement therapy to hypothyroid women should not be discontinued during pregnancy. Thyroid hormones undergo minimal placental transfer. Measure TSH and free-T4 as soon as pregnancy is confirmed and, at a minimum, during each trimester to gauge the adequacy of thyroid replacement dosage since during pregnancy as thyroid requirements may increase. For patients with serum TSH above the normal trimester-specific range, increase the dose of thyroid hormone and measure TSH every 4 weeks until a stable dose is reached and serum TSH is within the normal trimester-specific range. Immediately after obstetric delivery, the dosage should return to the pre-pregnancy dose, monitor thyroid function tests TSH at 4 to 8 weeks postpartum to assess for needed adjustments.[33700] [43942] [43943] [53562] [61764]
Breast-feeding
Levothyroxine is the preferential drug to treat hypothyroidism in most patients and is considered compatible with breast-feeding.[27500] [60310] Changes in thyroid status in the post-partum period may require careful monitoring and maternal dosage adjustment. In general, adequate thyroid status is needed to maintain normal lactation, and there is no reason maternal replacement should be halted due to lactation alone. Limited published studies report that levothyroxine is present in human milk. There is insufficient information to determine the effects of levothyroxine on the breastfed infant and no available information on the effects of levothyroxine on milk production. However, thyroid hormones do not have a known tumorigenic potential and are not associated with reports of serious adverse reactions in nursing infants.[27500] [33700] [43942] [43943] [43952] [53562] [61764]
Infertility
Levothyroxine use is only justified for treatment of female or male infertility if such infertility is accompanied by hypothyroidism.
Epiphyseal closure, hyperthyroidism, thyrotoxicosis
Guidelines recommend levothyroxine (T4) as the generally preferred treatment for hypothyroidism in adults, adolescents, children, infants, and neonates.[22902] [60310] However, there are case reports of patients whose TSH values could only be normalized with a combination of both T4 and T3 (liothyronine). Therefore, treatment must be individualized. Closely monitor all patients to avoid undertreatment or excessive treatment, which may produce hyperthyroidism or iatrogenic thyrotoxicosis.[60310] The management of hypothyroidism in pediatric patients is similar to adults, but there are unique differences based on the requirement of normal thyroid function for neurocognitive development as well as growth and development. There are increased weight-based requirements for thyroid hormone replacement in children and adolescents compared to adults. As the child advances through the pediatric age into adulthood, thyroid hormone replacement doses decrease, with a transition to the average adult dose once endocrine maturation is complete.[60310] Careful monitoring for growth, weight, epiphyseal closure and maturation, and clinical status are important in all pediatric patients. In patients with congenital hypothyroidism, closely monitor infants during the first 2 weeks of thyroid hormone therapy for cardiac overload, arrhythmias, and aspiration from avid suckling.[33700] [43942] [43943] [53562] [61764] Closely monitor all pediatric patients to avoid undertreatment or overtreatment. Undertreatment may have harmful effects on intellectual development and linear growth. Excessive treatment is associated with craniosynostosis in infants, may adversely affect the tempo of brain maturation, and may accelerate the bone age and result in premature epiphyseal closure and compromised adult stature. In children with acquired hypothyroidism, undertreatment may result in poor school performance due to impaired concentration and slowed mentation and in reduced adult height. Overtreatment may accelerate the bone age and result in premature epiphyseal closure and compromised adult stature. Treated children may manifest a period of catch-up growth, which may be adequate in some cases to normalize adult height. In children with severe or prolonged hypothyroidism, catch-up growth may not be adequate to normalize adult height.[33700] [43942] [43943] [53562] [61764]
DRUG INTERACTIONS
Acarbose: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, dosages are changed, or if thyroid hormones are discontinued.
Acetohexamide: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Albiglutide: (Minor) When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued. Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis.
Alendronate: (Moderate) Separating times of administration of alendronate from levothyroxine and other medications will maximize alendronate absorption and clinical benefit. For example, administering the levothyroxine dose at bedtime can avoid this interaction with alendronate. The bioavailability of alendronate was slightly decreased when alendronate and levothyroxine were co-administered to healthy subjects The mean AUC and Cmax of alendronate decreased by 7% and 9%, respectively. Alendronate should always be administered upon arising for the day and at least 30 minutes before the first food, beverage, or other medication of the day. To minimize interactions, levothyroxine is also best taken on an empty stomach with a glass of water.
Alendronate; Cholecalciferol: (Moderate) Separating times of administration of alendronate from levothyroxine and other medications will maximize alendronate absorption and clinical benefit. For example, administering the levothyroxine dose at bedtime can avoid this interaction with alendronate. The bioavailability of alendronate was slightly decreased when alendronate and levothyroxine were co-administered to healthy subjects The mean AUC and Cmax of alendronate decreased by 7% and 9%, respectively. Alendronate should always be administered upon arising for the day and at least 30 minutes before the first food, beverage, or other medication of the day. To minimize interactions, levothyroxine is also best taken on an empty stomach with a glass of water.
Alogliptin: (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued.
Alogliptin; Metformin: (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin. (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued.
Alogliptin; Pioglitazone: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, dosages are changed, or if thyroid hormones are discontinued. (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued.
Alpha-glucosidase Inhibitors: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, dosages are changed, or if thyroid hormones are discontinued.
Aluminum Hydroxide: (Moderate) To minimize an interaction, administer thyroid hormones at least 4 hours before or after antacids or other drugs containing aluminum hydroxide. Aluminum hydroxide, often found in antacids, interferes with the intestinal absorption of thyroid hormones. Gastric acidity is an essential requirement for adequate absorption of levothyroxine.
Aluminum Hydroxide; Magnesium Carbonate: (Moderate) To minimize an interaction, administer thyroid hormones at least 4 hours before or after antacids or other drugs containing aluminum hydroxide. Aluminum hydroxide, often found in antacids, interferes with the intestinal absorption of thyroid hormones. Gastric acidity is an essential requirement for adequate absorption of levothyroxine.
Aluminum Hydroxide; Magnesium Hydroxide: (Moderate) To minimize an interaction, administer thyroid hormones at least 4 hours before or after antacids or other drugs containing aluminum hydroxide. Aluminum hydroxide, often found in antacids, interferes with the intestinal absorption of thyroid hormones. Gastric acidity is an essential requirement for adequate absorption of levothyroxine.
Aluminum Hydroxide; Magnesium Hydroxide; Simethicone: (Moderate) Oral thyroid hormones should be administered at least 4 hours before or after a dose of simethicone. Concurrent use may reduce the efficacy of levothyroxine by binding and delaying or preventing oral absorption, potentially resulting in hypothyroidism. Simethicone has been reported to chelate oral levothyroxine within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. (Moderate) To minimize an interaction, administer thyroid hormones at least 4 hours before or after antacids or other drugs containing aluminum hydroxide. Aluminum hydroxide, often found in antacids, interferes with the intestinal absorption of thyroid hormones. Gastric acidity is an essential requirement for adequate absorption of levothyroxine.
Aluminum Hydroxide; Magnesium Trisilicate: (Moderate) To minimize an interaction, administer thyroid hormones at least 4 hours before or after antacids or other drugs containing aluminum hydroxide. Aluminum hydroxide, often found in antacids, interferes with the intestinal absorption of thyroid hormones. Gastric acidity is an essential requirement for adequate absorption of levothyroxine.
Amiodarone: (Moderate) Amiodarone has a complex effect on the metabolism of thyroid hormones and can alter thyroid function tests in many patients. Since approximately 37% of amiodarone (by weight) is iodine, maintenance doses of 200 to 600 mg of amiodarone/day result in ingestion of 75 to 225 mg/day of organic iodide, resulting in much higher total iodine stores in the body. In addition, amiodarone decreases T4 5'-deiodinase activity, which decreases the peripheral conversion of T4 to T3, leading to decreased serum T3. Serum T4 levels are usually normal but may be slightly increased. TSH concentrations usually increase during amiodarone therapy, but after 3 months of continuous administration, TSH concentrations often return to normal. However, amiodarone can cause hypothyroidism or hyperthyroidism, including life-threatening thyrotoxicosis. Therefore, patients receiving levothyroxine and amiodarone should be monitored for changes in thyroid function; because of the slow elimination of amiodarone and its metabolites, abnormal thyroid function tests may persists for weeks or months after amiodarone drug discontinuation.
Amobarbital: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Amoxapine: (Minor) Thyroid hormones may increase receptor sensitivity and enhance the effects of amoxapine. Although this drug combination appears to be safe, clinicians should be aware of the remote possibility of exaggerated cardiovascular side effects such as arrhythmias and CNS stimulation.
Amoxicillin; Clarithromycin; Omeprazole: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Asparaginase Erwinia chrysanthemi: (Moderate) Some hypothyroid patients receiving asparaginase may require reduced doses of thyroid hormone. Other patients may remain euthyroid during combined treatment. Monitor TSH levels and monitor for symptoms of hyperthyroidism; a free-T4 concentration may be useful to assess euthyroidism. Asparaginase may decrease the serum TBG (thyroxine-binding globulin) concentration. Decreased amounts of TBG may result in an increased clinical response to thyroid hormones.
Aspirin, ASA; Butalbital; Caffeine: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Aspirin, ASA; Butalbital; Caffeine; Codeine: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Aspirin, ASA; Omeprazole: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Barbiturates: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Beta-agonists: (Moderate) Monitor blood pressure and heart rate during concomitant beta-agonist and thyroid hormone use. Concurrent use may increase the effects of sympathomimetics or thyroid hormone. Thyroid hormones may increase the risk of coronary insufficiency when sympathomimetic agents are administered to patients with coronary artery disease.
Beta-blockers: (Minor) Because thyroid hormones cause cardiac stimulation including increased heart rate and increased contractility, the effects of beta-blockers may be reduced by thyroid hormones. The reduction of effects may be especially evident when a patient goes from a hypothyroid to a euthyroid state or when excessive amounts of thyroid hormone is given to the patient.
Butabarbital: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Butalbital; Acetaminophen: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Butalbital; Acetaminophen; Caffeine: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Butalbital; Acetaminophen; Caffeine; Codeine: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Calcium Acetate: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Calcium Carbonate: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Calcium Carbonate; Famotidine; Magnesium Hydroxide: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Calcium Carbonate; Magnesium Hydroxide: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Calcium Carbonate; Magnesium Hydroxide; Simethicone: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Calcium Carbonate; Risedronate: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Calcium Carbonate; Simethicone: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Calcium Chloride: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Calcium Gluconate: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Calcium: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Calcium; Vitamin D: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Canagliflozin: (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued.
Canagliflozin; Metformin: (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin. (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued.
Carbamazepine: (Minor) Use carbamazepine and thyroid hormones together with caution. Carbamazepine may inhibit the binding of thyroid hormones to carrier proteins, resulting in a transient increase in free thyroid hormones followed by an overall decrease in total thyroid hormone concentrations. Carbamazepine reduces serum protein binding of levothyroxine, and total and free-T4 may be reduced by 20% to 40%, but most patients have normal serum TSH levels and are clinically euthyroid. Monitor thyroid hormone parameters.
Chlorpropamide: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Cholestyramine: (Moderate) Administer oral levothyroxine or other oral thyroid hormones at least 4 hours before a dose of cholestyramine. Cholestyramine and other bile acid sequestrants have been shown to decrease the oral absorption of thyroid hormones. Monitor thyroid function periodically to ensure proper clinical management.
Chromium: (Moderate) Advise patients to separate chromium supplement ingestion from taking their oral thyroid hormone. For example, taking oral thyroid hormones 1 hours before or 3 hours after chromium picolinate ingestion should minimize an interaction. Chromium could potentially decrease the oral absorption of thyroid hormones. In one study of normal volunteers, the subjects (n = 7) ingested levothyroxine sodium, either taken separately or co-administered with chromium picolinate. Serum thyroxine was measured at intervals over a 6-hour period following drug ingestion. Chromium picolinate significantly decreased the serum thyroxine concentrations. (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Cocaine: (Moderate) The concomitant use of sympathomimetics and thyroid hormones can enhance the effects on the cardiovascular system. Patients with coronary artery disease have an increased risk of coronary insufficiency from either agent. Concomitant use of these agents may increase this risk further.
Colesevelam: (Moderate) Administer oral levothyroxine or other oral thyroid hormones at least 4 hours before a dose of colesevelam. Colesevelam and other bile acid sequestrants have been shown to decrease the oral absorption of thyroid hormones. Monitor thyroid function periodically to ensure proper clinical management.
Colestipol: (Moderate) Administer oral levothyroxine or other oral thyroid hormones at least 4 hours before a dose of colestipol. Colestipol and other bile acid sequestrants have been shown to decrease the oral absorption of thyroid hormones. Monitor thyroid function periodically to ensure proper clinical management.
Cyclosporine: (Moderate) Serum trough cyclosporine concentrations appear to be reduced by concurrent oral cyclosporine and levothyroxine use. Claosely monitor cyclosporine concentrations with concomitant levothyroxine therapy. Among 10 patients who took cyclosporine (Neoral) capsules twice daily for at least a year and oral levothyroxine 100 mcg daily for at least 3 months, the trough serum cyclosporine concentration was significantly lower as compared with values from 30 patients who only took cyclosporine. The mechanism of the interaction may be decreased oral cyclosporine absorption. Cyclosporine is a substrate of P-glycoprotein (P-gp), and levothyroxine appears to be an inducer of intestinal P-gp.
Dapagliflozin: (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued.
Dapagliflozin; Metformin: (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin. (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued.
Dapagliflozin; Saxagliptin: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed. (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued.
Dexlansoprazole: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Didanosine, ddI: (Moderate) Oral thyroid hormones should be taken at least 2 hours before the administration of certain didanosine formulations to avoid an interaction. Certain didanosine, ddI formulations contain buffers (e.g., chewable/dispersible tablets and oral powder for solution) or are mixed with antacids (e.g., pediatric powder for oral solution). Thyroid hormones are susceptible to drug interactions with buffers/antacids containing aluminum, magnesium, or calcium, which may chelate thyroid hormones within the GI tract and decrease oral thyroid hormone absorption. Gastric acidity is also an essential requirement for adequate absorption of levothyroxine. Hypothyroidism may occur if doses are not separated. The delayed-release didanosine capsules (e.g., Videx EC) do not contain a buffering agent and are not expected to interact with thyroid hormones.
Digoxin: (Minor) Thyroid disease is known to alter the response to digoxin. Digoxin toxicity is more likely to occur in patients with hypothyroidism, while the response to digoxin is diminished in patients with hyperthyroidism. These reactions should be kept in mind when therapy with thyroid hormones is begun or interrupted. When hypothyroid patients are administered thyroid hormone, the dose requirement of digoxin may be increased.
Dulaglutide: (Minor) When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued. Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis.
Empagliflozin: (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued.
Empagliflozin; Linagliptin: (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued. (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents, such as linagliptin, if thyroid hormones are added or discontinued.
Empagliflozin; Linagliptin; Metformin: (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin. (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued. (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents, such as linagliptin, if thyroid hormones are added or discontinued.
Empagliflozin; Metformin: (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin. (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued.
Enteral Feedings: (Contraindicated) Certain foods, beverages, and enteral feedings can inhibit the absorption of thyroid hormones. To minimize the risk of an interaction, thyroid hormones should be administered on an empty stomach with a glass of water at least 30 to 60 minutes prior to food or enteral feedings. Foods that may decrease thyroid hormone absorption include soybean flour and soy-based infant formulas or enteral feedings, as well as high fiber diets, cottonseed meal, and walnuts. In addition to decreasing the oral absorption of thyroid hormones, limited data indicate that soy containing foods and supplements may also influence thyroid physiology. Concentrated soy isoflavones (e.g., genistein and daidzein) may interfere with thyroid peroxidase catalyzed iodination of thyroglobulin, resulting in a decreased production of thyroid hormones and an increased secretion of TSH endogenously. More studies are required to assess the exact mechanism of this interaction. Caution should be used in administering soy isoflavone supplements concurrently with thyroid hormones. Limited data show that coffee has the potential to impair T4 intestinal absorption. In one report, T4 intestinal absorption was evaluated after the administration of 200 mcg L-thyroxine (L-T4) swallowed with coffee/espresso, water, or water followed 60 minutes later by coffee/espresso. Researchers found that administration with coffee/espresso significantly lowered average serum T4 (p<0.001) and peak serum T4 concentrations (p<0.05) when compared to L-T4 taken with water alone. Coffee/espresso taken 60 minutes after L-T4 ingestion had no significant effect on T4 intestinal absorption. It is prudent to remind patients that thyroid hormones should be separated from food and beverages (other than water), including coffee, by at least 30 to 60 minutes.
Ertugliflozin; Metformin: (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin.
Ertugliflozin; Sitagliptin: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Esomeprazole: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Estrogens: (Minor) The administration of estrogens can increase circulating concentrations of thyroxine-binding globulin, sex hormone-binding globulin, and cortisol-binding globulin. Increased amounts of thyroxine-binding globulin may result in a reduced clinical response to thyroid hormones. Some hypothyroid patients on estrogen may require larger doses of thyroid hormones. Monitor thyroid-stimulating hormone (TSH) level and follow the recommendation for thyroid hormone replacement.
Exenatide: (Minor) When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued. Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis.
Ferric Maltol: (Moderate) Oral thyroid hormones should be administered at least 4 hours before or after the ingestion of iron supplements. Oral iron salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased oral absorption of the thyroid hormone. For example, ferrous sulfate likely forms a ferric-thyroxine complex.
Fluoxymesterone: (Moderate) Coadministration may result in increased thyroid hormone concentrations. Monitor thyroid function during concomitant use in patients taking thyroid hormones. In some patients, the thyroid hormone dosage may need to be reduced. Androgens, such as fluoxymesterone may decrease levels of thyroxine-binding globulin, resulting in decreased total T4 serum levels and increased resin uptake of T3 and T4. Free thyroid hormone levels remain unchanged, however, and there is no clinical evidence of thyroid dysfunction in patients without thyroid disease. However, a lowered need for thyroid hormone has been noticed in hypothyroid patients in one publication.
Folic Acid, Vitamin B9: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Food: (Contraindicated) Certain foods, beverages, and enteral feedings can inhibit the absorption of thyroid hormones. To minimize the risk of an interaction, thyroid hormones should be administered on an empty stomach with a glass of water at least 30 to 60 minutes prior to food or enteral feedings. Foods that may decrease thyroid hormone absorption include soybean flour and soy-based infant formulas or enteral feedings, as well as high fiber diets, cottonseed meal, and walnuts. In addition to decreasing the oral absorption of thyroid hormones, limited data indicate that soy containing foods and supplements may also influence thyroid physiology. Concentrated soy isoflavones (e.g., genistein and daidzein) may interfere with thyroid peroxidase catalyzed iodination of thyroglobulin, resulting in a decreased production of thyroid hormones and an increased secretion of TSH endogenously. More studies are required to assess the exact mechanism of this interaction. Caution should be used in administering soy isoflavone supplements concurrently with thyroid hormones. Limited data show that coffee has the potential to impair T4 intestinal absorption. In one report, T4 intestinal absorption was evaluated after the administration of 200 mcg L-thyroxine (L-T4) swallowed with coffee/espresso, water, or water followed 60 minutes later by coffee/espresso. Researchers found that administration with coffee/espresso significantly lowered average serum T4 (p<0.001) and peak serum T4 concentrations (p<0.05) when compared to L-T4 taken with water alone. Coffee/espresso taken 60 minutes after L-T4 ingestion had no significant effect on T4 intestinal absorption. It is prudent to remind patients that thyroid hormones should be separated from food and beverages (other than water), including coffee, by at least 30 to 60 minutes.
Furosemide: (Moderate) Use high doses (more than 80 mg) of furosemide and thyroid hormones together with caution. High doses of furosemide may inhibit the binding of thyroid hormones to carrier proteins, resulting in a transient increase in free thyroid hormones followed by an overall decrease in total thyroid hormone concentrations.
Glimepiride: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Glimepiride; Rosiglitazone: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed. (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, dosages are changed, or if thyroid hormones are discontinued.
Glipizide: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Glipizide; Metformin: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed. (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin.
Glyburide: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Glyburide; Metformin: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed. (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin.
Hydantoins: (Minor) Hydantoin anticonvulsants induce hepatic microsomal enzymes and may increase the metabolism of thyroid hormones, leading to reduced efficacy of the thyroid hormone.
Imatinib: (Moderate) Monitor thyroid stimulating hormone (TSH) concentrations carefully when tyrosine kinase inhibitors like imatinib are used in patients taking thyroid hormones. Cases of clinical hypothyroidism have occurred in patients taking imatinib.
Indinavir: (Moderate) Closely monitor the thyroid status of any patient taking thyroid hormones concurrently with indinavir. Hyperthyroidism was reported in a patient when indinavir was added to a stable levothyroxine dosing regimen. Indinavir inhibits UDP-glucuronosyl transferase, which may have decreased the metabolism of the thyroid hormone and may explain the increased thyroxine levels observed. Patients receiving levothyroxine should be carefully monitored when indinavir is started; if hyperthyroidism is detected, reducing the levothyroxine dose should reestablish a euthyroid state. Theoretically, similar interactions may occur between indinavir and other thyroid hormones, given that both T4 and T3 are metabolized to some degree via hepatic UDP-glucuronosyl transferase.
Insulin Degludec; Liraglutide: (Minor) When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued. Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis.
Insulin Glargine; Lixisenatide: (Minor) When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued. Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis.
Insulins: (Minor) Monitor patients receiving insulin closely for changes in diabetic control whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued. Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced.
Iodine; Potassium Iodide, KI: (Moderate) Antithyroid agents should generally not be administered with the thyroid hormones due to their opposing effects. However, in selected cases some clinicians coadminister T4 (e.g., levothyroxine) to circumvent drug-induced hypothyroidism when large suppressive doses of antithyroid agents are administered for long periods of time. However, clinical and biochemical euthyroid status may usually be maintained with careful titration of the antithyroid agent dosage alone.
Iodoquinol: (Moderate) Iodoquinol should be used with caution in patients treated with thyroid hormones. Iodine-containing compounds like iodoquinol may result in overt thyroid disease. Increased uptake of iodine by the thyroid may lead to changes in thyroid status, especially in patients with pre-existing thyroid disease. Iodoquinol has been shown to interfere with thyroid function tests for up to 6 months.
Iron Salts: (Moderate) Oral thyroid hormones should be administered at least 4 hours before or after the ingestion of iron supplements. Oral iron salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased oral absorption of the thyroid hormone. For example, ferrous sulfate likely forms a ferric-thyroxine complex.
Iron Sucrose, Sucroferric Oxyhydroxide: (Moderate) Administer oral thyroid hormones at least 4 hours before or after oral iron sucrose, sucroferric oxyhydroxide. Oral iron salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral iron supplements.
Iron: (Moderate) Oral thyroid hormones should be administered at least 4 hours before or after the ingestion of iron supplements. Oral iron salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased oral absorption of the thyroid hormone. For example, ferrous sulfate likely forms a ferric-thyroxine complex.
Isoniazid, INH; Pyrazinamide, PZA; Rifampin: (Moderate) Rifampin increases thyroid hormone metabolism by inducing uridine 5-diphospho-glucuronosyltransferase (UGT) and leads to lower T4 serum levels. Clinicians should be alert for a decreased response to thyroid hormones if rifampin is used during thyroid hormone therapy.
Isoniazid, INH; Rifampin: (Moderate) Rifampin increases thyroid hormone metabolism by inducing uridine 5-diphospho-glucuronosyltransferase (UGT) and leads to lower T4 serum levels. Clinicians should be alert for a decreased response to thyroid hormones if rifampin is used during thyroid hormone therapy.
Ketamine: (Moderate) Ketamine should be administered cautiously to patients receiving levothyroxine because concomitant use can cause marked hypertension and tachycardia.
Lansoprazole: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Lansoprazole; Amoxicillin; Clarithromycin: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Lansoprazole; Naproxen: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Lanthanum Carbonate: (Moderate) Administer oral thyroid hormones at least 4 hours before or after the administration of lanthanum carbonate. Concurrent use may reduce the efficacy of levothyroxine by binding and delaying or preventing oral absorption, potentially resulting in hypothyroidism. Thyroid stimulating hormone (TSH) concentrations should be carefully monitored. The bioavailability of levothyroxine was decreased by approximately 40% when administered with lanthanum carbonate.
L-Asparaginase Escherichia coli: (Moderate) Some hypothyroid patients receiving asparaginase may require reduced doses of thyroid hormone. Other patients may remain euthyroid during combined treatment. Monitor TSH levels and monitor for symptoms of hyperthyroidism; a free-T4 concentration may be useful to assess euthyroidism. Asparaginase may decrease the serum TBG (thyroxine-binding globulin) concentration. Decreased amounts of TBG may result in an increased clinical response to thyroid hormones.
Linagliptin: (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents, such as linagliptin, if thyroid hormones are added or discontinued.
Linagliptin; Metformin: (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin. (Minor) Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis. When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use oral antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents, such as linagliptin, if thyroid hormones are added or discontinued.
Liraglutide: (Minor) When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued. Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis.
Lixisenatide: (Minor) When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued. Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis.
Lonapegsomatropin: (Minor) Excessive use of thyroid hormones with growth hormone (somatropin, rh-GH) may accelerate epiphyseal closure. However, untreated hypothyroidism may interfere with growth response to somatropin. Patients receiving concomitant therapy should be monitored closely to ensure appropriate therapeutic response to somatropin.
Magnesium: (Moderate) Administer thyroid hormones at least 4 hours before or after antacids, dietary supplements, or other drugs containing magnesium. Magnesium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of levothyroxine with products containing oral cations, such as antacids or dietary supplements.
Maprotiline: (Minor) Thyroid hormones may increase receptor sensitivity and enhance the effects of maprotiline.
Meglitinides: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Metformin: (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin.
Metformin; Repaglinide: (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin.
Metformin; Rosiglitazone: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, dosages are changed, or if thyroid hormones are discontinued. (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin.
Metformin; Saxagliptin: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed. (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin.
Metformin; Sitagliptin: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed. (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin.
Methohexital: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Miglitol: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, dosages are changed, or if thyroid hormones are discontinued.
Naproxen; Esomeprazole: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Norethindrone Acetate; Ethinyl Estradiol; Ferrous fumarate: (Moderate) Oral thyroid hormones should be administered at least 4 hours before or after the ingestion of iron supplements. Oral iron salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased oral absorption of the thyroid hormone. For example, ferrous sulfate likely forms a ferric-thyroxine complex.
Norethindrone; Ethinyl Estradiol; Ferrous fumarate: (Moderate) Oral thyroid hormones should be administered at least 4 hours before or after the ingestion of iron supplements. Oral iron salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased oral absorption of the thyroid hormone. For example, ferrous sulfate likely forms a ferric-thyroxine complex.
Omeprazole: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Omeprazole; Amoxicillin; Rifabutin: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Omeprazole; Sodium Bicarbonate: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Orlistat: (Moderate) Oral thyroid hormones should be administered at least 4 hours before or after a dose of orlistat. Concurrent use may reduce the efficacy of thyroid hormones by binding and delaying or preventing oral absorption, potentially resulting in hypothyroidism. Monitor TSH while orlistat is used concurrently. Hypothyroidism has been reported in patients treated concomitantly with orlistat and levothyroxine postmarketing.
Pantoprazole: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Pentobarbital: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Phenobarbital: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Phenobarbital; Hyoscyamine; Atropine; Scopolamine: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Pioglitazone: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, dosages are changed, or if thyroid hormones are discontinued.
Pioglitazone; Glimepiride: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed. (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, dosages are changed, or if thyroid hormones are discontinued.
Pioglitazone; Metformin: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, dosages are changed, or if thyroid hormones are discontinued. (Minor) Thyroid hormone use may result in increased blood sugar and a loss of glycemic control in some patients. Interactions may or may not be clinically significant at usual replacement doses. Monitor blood sugars carefully when thyroid therapy is added, changed, or discontinued in patients receiving metformin.
Polycarbophil: (Moderate) Administer thyroid hormones at least 2 hours before or after the ingestion of calcium polycarbophil. Thyroid hormones are best taken on an empty stomach, and, administration should be separated from medications that might interfere with absorption. Monitor the patient's thyroid function and clinical status if the patient is on calcium polycarbophil treatment. Dietary fiber may bind and decrease the absorption of thyroid hormones from the gastrointestinal tract. Each 625 mg of calcium polycarbophil contains a substantial amount of calcium (approximately 125 mg). Calcium salts can chelate oral thyroid hormones within the GI tract when administered simultaneously, also leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from calcium supplements and thyroid hormone interactions. In a study of 8 volunteers, the absorption of levothyroxine decreased from 89% when administered alone to only 86% when administered concomitantly with 1,000 mg of calcium polycarbophil.
Polysaccharide-Iron Complex: (Moderate) Oral thyroid hormones should be administered at least 4 hours before or after the ingestion of iron supplements. Oral iron salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased oral absorption of the thyroid hormone. For example, ferrous sulfate likely forms a ferric-thyroxine complex.
Potassium Iodide, KI: (Moderate) Antithyroid agents should generally not be administered with the thyroid hormones due to their opposing effects. However, in selected cases some clinicians coadminister T4 (e.g., levothyroxine) to circumvent drug-induced hypothyroidism when large suppressive doses of antithyroid agents are administered for long periods of time. However, clinical and biochemical euthyroid status may usually be maintained with careful titration of the antithyroid agent dosage alone.
Pramlintide: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, dosages are changed, or if thyroid hormones are discontinued.
Primidone: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Propylthiouracil, PTU: (Major) Antithyroid agents should generally not be administered with the thyroid hormones due to their opposing effects. However, in selected cases some clinicians co-administer T4 (e.g., levothyroxine) to circumvent drug-induced hypothyroidism when large suppressive doses of antithyroid agents are administered for long periods of time. However, clinical and biochemical euthyroid status may usually be maintained with careful titration of the antithyroid agent dosage alone.
Proton pump inhibitors: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Pyridoxine, Vitamin B6: (Moderate) Thyroid hormones should be administered at least 4 hours before or after the ingestion of oral calcium supplements. Calcium salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption. Some case reports have described clinical hypothyroidism resulting from coadministration of thyroid hormones with oral calcium supplements.
Rabeprazole: (Moderate) The use of proton pump inhibitors may result in decreased effectiveness of thyroid hormone therapy. Monitor clinically for signs and symptoms of hypothyroidism and altered response to thyroid hormone therapy. Periodically assess the TSH during use of these drugs together. Gastric acidity is an essential requirement for proper and adequate absorption of levothyroxine and other thyroid hormones. Proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce thyroid hormone absorption.
Raloxifene: (Moderate) Patients prescribed raloxifene while taking thyroid hormones should be advised to take the drugs at separate times (e.g., 12 hours apart) until more data are available. Raloxifene may delay and reduce the oral absorption of levothyroxine (T4). In a case report, a patient with chronic but treated hypothyroidism was taking a stable dose of levothyroxine. The patient required increasing doses of levothyroxine when raloxifene was coadministered; the TSH level remained elevated and serum T4 remained decreased despite an increase in oral levothyroxine dosage. An absorption interaction was suspected and the patient rechallenged on two occasions; a decrease in serum T4 was observed whenever raloxifene and levothyroxine were administered concurrently. The patient's levothyroxine dosage requirements returned to baseline and the TSH value normalized when levothyroxine and raloxifene were administered 12 hours apart rather than simultaneously. The mechanism for the observed interaction is unknown. In theory, raloxifene might cause oral malabsorption of any thyroid hormone containing T4 (e.g., desiccated thyroid, levothyroxine, liotrix) if administered at the same time.
Rifampin: (Moderate) Rifampin increases thyroid hormone metabolism by inducing uridine 5-diphospho-glucuronosyltransferase (UGT) and leads to lower T4 serum levels. Clinicians should be alert for a decreased response to thyroid hormones if rifampin is used during thyroid hormone therapy.
Rosiglitazone: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, dosages are changed, or if thyroid hormones are discontinued.
Saxagliptin: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Secobarbital: (Minor) Hepatic enzyme-inducing drugs, including barbiturates, can increase the catabolism of thyroid hormones. Be alert for a decreased response to thyroid replacement agents with dosage adjustments, discontinuation or addition of barbiturates during thyroid hormone replacement therapy.
Semaglutide: (Moderate) Consider additional thyroid function monitoring during concomitant use of oral thyroid hormones and oral semaglutide. Advise patients to take oral semaglutide 30 minutes before other oral medications. Concomitant use has been observed to increase levothyroxine exposure by 33% which may increase the risk for symptoms of hyperthyroidism or require a dosage adjustment. Semaglutide delays gastric emptying which may affect the absorption of other orally administered medications. This absorption interaction is not expected with subcutaneous semaglutide or intravenous levothyroxine. Additionally, levothyroxine may worsen glycemic control in patients with diabetes.
Sevelamer: (Moderate) Thyroid hormone oral administration should be separated from sevelamer administration by 4 hours. Sevelamer appears to decrease the oral absorption of thyroid hormones. In one study of normal volunteers, the subjects (n = 7) ingested orally levothyroxine sodium, either taken separately or coadministered with sevelamer. Serum thyroxine was measured at intervals over a 6-hour period following drug ingestion. Sevelamer significantly decreased the the serum thyroxine concentration. The authors concluded that patients should be advised to separate the time of ingestion of sevelamer from their thyroid hormone preparation.
Simethicone: (Moderate) Oral thyroid hormones should be administered at least 4 hours before or after a dose of simethicone. Concurrent use may reduce the efficacy of levothyroxine by binding and delaying or preventing oral absorption, potentially resulting in hypothyroidism. Simethicone has been reported to chelate oral levothyroxine within the GI tract when administered simultaneously, leading to decreased thyroid hormone absorption.
Simvastatin; Sitagliptin: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Sitagliptin: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Sodium Ferric Gluconate Complex; ferric pyrophosphate citrate: (Moderate) Oral thyroid hormones should be administered at least 4 hours before or after the ingestion of iron supplements. Oral iron salts have been reported to chelate oral thyroid hormones within the GI tract when administered simultaneously, leading to decreased oral absorption of the thyroid hormone. For example, ferrous sulfate likely forms a ferric-thyroxine complex.
Sodium Iodide: (Major) In order to increase thyroid uptake and optimize exposure of thyroid tissue to the radionucleotide, patients must discontinue all medications and supplements that may interfere with iodide uptake into thyroid tissue prior to therapy with sodium iodide I-131, including thyroid hormones. Although various protocols are used, the following withdrawal timing recommendations were set forth in a procedure guideline published by the Society of Nuclear Medicine in February 2002. It is recommended to hold alll T4 thyroid hormones (e.g., levothyroxine) 4 to 6 weeks prior, and to hold all T3 thyroid hormones (e.g., liothyronine) 2 weeks prior, to sodium iodide I-131 therapy.
Sodium Polystyrene Sulfonate: (Moderate) Administer thyroid hormones at least 4 hours apart from cation exchange resins, like sodium polystyrene sulfonate. Cation exchange resins can bind thyroxine or levothyroxine in the GI tract and inhibit oral absorption, potentially leading to hypothyroidism.
Somatropin, rh-GH: (Minor) Excessive use of thyroid hormones with growth hormone (somatropin, rh-GH) may accelerate epiphyseal closure. However, untreated hypothyroidism may interfere with growth response to somatropin. Patients receiving concomitant therapy should be monitored closely to ensure appropriate therapeutic response to somatropin.
Soy Isoflavones: (Moderate) Concentrated soy isoflavones (e.g., genistein and daidzein) may interfere with thyroid peroxidase catalyzed iodination of thyroglobulin, resulting in a decreased production of thyroid hormones and an increased secretion of TSH endogenously. Caution should be used in administering soy isoflavone supplements concurrently with thyroid hormones. More studies are required to assess the exact mechanism of this interaction.
Sucralfate: (Moderate) Administer levothyroxine at least 4 hours apart from a dose of sucralfate. Patients treated concomitantly with these drugs should be monitored for changes in thyroid function. Consider an alternative to sucralfate, if appropriate. Concurrent use of sucralfate may reduce the efficacy of levothyroxine and other thyroid hormones by binding and delaying or preventing oral absorption, potentially resulting in hypothyroidism.
Sulfonylureas: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Sympathomimetics: (Moderate) Monitor hemodynamic parameters during concomitant sympathomimetic agent and thyroid hormone use; dosage adjustments may be necessary. Concomitant use may increase the effects of sympathomimetics or thyroid hormone.
Teduglutide: (Moderate) Monitor thyroid status and for symptoms of increased thyroid effect. Based upon the pharmacodynamic effect of teduglutide, there is a potential for increased absorption of concomitant oral medications, which should be considered if these drugs require titration or have a narrow therapeutic index, such as orally administered thyroid hormones.
Theophylline, Aminophylline: (Minor) Correction of hypothyroidism to the euthyroid state may precipitate certain drug interactions. For example, hypothyroidism causes decreased clearance of theophylline, which returns to normal in the euthyroid state. Aminophylline is converted to theophylline in the body. Aminophylline dosage adjustments may be needed with thyroid hormone replacement. (Minor) Correction of hypothyroidism to the euthyroid state may precipitate certain drug interactions. For example, hypothyroidism causes decreased clearance of theophylline, which returns to normal in the euthyroid state. Theophylline dosage adjustments may be needed with thyroid hormone replacement.
Thiazolidinediones: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, dosages are changed, or if thyroid hormones are discontinued.
Tirofiban: (Minor) Data from the PRISM study, indicate that patients who received levothyroxine or omeprazole concomitantly with tirofiban had a higher rate of tirofiban clearance than patients who did not receive levothyroxine or omeprazole. The clinical significance of this is unknown.
Tirzepatide: (Minor) When thyroid hormones are added to existing diabetes therapy, the glucose-lowering effect may be reduced. Close monitoring of blood glucose is necessary for individuals who use antidiabetic agents whenever there is a change in thyroid treatment. It may be necessary to adjust the dose of antidiabetic agents if thyroid hormones are added or discontinued. Thyroid hormones are important in the regulation of carbohydrate metabolism, gluconeogenesis, the mobilization of glycogen stores, and protein synthesis.
Tolazamide: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Tolbutamide: (Minor) Addition of thyroid hormones to antidiabetic or insulin therapy may result in increased dosage requirements of the antidiabetic agents. Blood sugars should be carefully monitored when thyroid therapy is added, discontinued or doses changed.
Tretinoin, ATRA: (Moderate) The concomitant use of systemic tretinoin, ATRA and thyroid hormones should be done cautiously due to the potential for increased intracranial pressure and an increased risk of pseudotumor cerebri (benign intracranial hypertension). Early signs and symptoms of pseudotumor cerebri include papilledema, headache, nausea, vomiting, and visual disturbances.
Tricyclic antidepressants: (Minor) Thyroid hormones may increase receptor sensitivity and enhance the effects of tricyclic antidepressants. Although this drug combination appears to be safe, be aware of the possibility of exaggerated cardiovascular side effects such as arrhythmias and CNS stimulation.
Vonoprazan; Amoxicillin: (Moderate) Monitor for altered response to thyroid hormones if coadministered with vonoprazan. Vonoprazan reduces intragastric acidity, which may decrease the absorption of oral thyroid hormones reducing their efficacy.
Vonoprazan; Amoxicillin; Clarithromycin: (Moderate) Monitor for altered response to thyroid hormones if coadministered with vonoprazan. Vonoprazan reduces intragastric acidity, which may decrease the absorption of oral thyroid hormones reducing their efficacy.
Warfarin: (Moderate) The concurrent use of thyroid hormones and warfarin potentiates anticoagulation effects of warfarin. The mechanism of this interaction may be the increased catabolism of vitamin K clotting factors as the hypothyroid state is corrected. As a result, the hypoprothrombinemic response to warfarin occurs earlier and to a greater degree. Dextrothyroxine has been shown to potentiate the effects of warfarin. Dextrothyroxine may increase the affinity of warfarin for its receptor sites in addition to increasing the catabolism of vitamin K dependent clotting factors. A reduction in the dosage of warfarin is recommended with concomitant therapy.