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While the search for a viable male contraceptive continues, a new non-hormonal male contraceptive has been gaining traction over recent years. Researcher Sujoy Guha of India first published a paper on a promising new non-hormonal male contraceptive in the journal Contraception in 1979, which he dubbed Reversible Inhibition of Sperm Under Guidance (RISUG). The technique relies on a polymer gel that is injected into the vas deferens, occluding the passage of sperm. In addition, the gel carries a positive charge that acts as a buffer on negatively charged sperm, damages their heads and tails, and renders them infertile. It is reversed with a second shot that breaks down the gel, allowing sperm to reach the penis normally. While RISUG has been steadily making its way through clinical trials in India, the technology was licensed to the Parsemus Foundation, a US-based nonprofit company that has dubbed their formulation of the polymer hydrogel Vasalgel.
So far, the only trials of Vasalgel in the US have been on animals. In 2016, the Parsemus Foundation published a study to determine the contraceptive efficacy of two polymer formulations with different levels of styrene maleic acid (SMA), 100% vs. 80% acid and 20% anhydride, on 15 mature male rabbits accompanied by three mature female rabbits. Over the 12-month period, researchers analyzed semen parameters regarding sperm concentration, motility and forward progression. Both the concentration of SMA produced rapid onset of azoospermia, with no sperm in semen samples collected as early as 29–36 days post-implantation and durable throughout the year, proving the effectiveness of the polymer in the rabbit model.
A follow-up study published in 2017 evaluated the reversal procedure in the rabbit model. After 14 months of azoospermia, sodium bicarbonate was injected into the vasa deferentia, flushing the polymer out of the tubes. Sperm characteristics were collected for 12 months post-injection and sperm concentration and motility were comparable to baseline levels after reversal. In addition to the rabbit models, one study looked at the efficacy of Vasalgel in 16 adult male rhesus monkeys. After a one-week recovery, the males were placed in outdoor group housing, which included at least 3 and up to 9 intact, breeding females with a successful reproductive history. Throughout the 2-year period, there were no conceptions within the free-living group environment.
Although studies on Vasalgel have only been completed on animal models, the Parsemus Foundation stated that it plans to begin human trials in 2018 based on the previous successful animal data. Also, additional reversibility studies must be completed before the reversibility of Vasalgel can be confirmed and the product can be marketed as a reversible male contraceptive. The foundation aims for Vasalgel to be available worldwide, with a tiered international pricing structure to ensure affordability to all men. The specific side effects of Vasalgel can only be determined through clinical experience. Two more common concerns regarding vasectomy are the development of sperm granulomas and pressure buildup. Sperm granulomas are formed when the vas deferens is severed in a vasectomy and sperm leak into surrounding tissue. Since injection of Vasalgel does not involve cutting the vas deferens, this may not be an issue. According to the American Urological Association, 1–2% of men who have had a vasectomy experience chronic pain, which may be due to back-pressure. Vasalgel is designed such that fluids may pass through the gel, but sperm cannot, which will potentially reduce the amount of back-pressure. In the limited field of male contraceptives, Vasalgel is a promising new technique to keep an eye on.
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Colagross-Schouten A, Lemoy M, Keesler RI, et al. The contraceptive efficacy of intravas injection of Vasalgel™ for adult male rhesus monkeys. Basic Clin Androl 2017;27:4. https://bacandrology.biomedcentral.com/articles/10.1186/s12610-017-0048-9
Vasalgel, a Multi-Year Contraceptive. Parsemus Foundation website. https://www.parsemusfoundation.org/projects/vasalgel/. Updated November 20, 2017. Accessed March 9, 2018.
Waller D, Bolick D, Lissner E, et al. Azoospermia in rabbits following an intravas injection of Vasalgel. Basic Clin Androl 2016;26:6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4812607/
Waller D, Bolick D, Lissner E. Reversibility of Vasalgel male contraceptive in a rabbit model. Basic Clin Andro 2017;27:8. https://bacandrology.biomedcentral.com/articles/10.1186/s12610-017-0051-1