The burden of birth control has long fallen on women. There are numerous more forms of birth control available to women–ranging from oral pills to internal IUDs–than men, who rely primarily upon condoms. Vasectomy is the sole long-acting method available to men. Now, however, researchers from the California National Primate Research Center at University of California, Davis, have successfully tested the effectiveness of a new contraceptive gel called Vasalgel™, in adult male rhesus monkeys living in small group housing for at least one breeding season and up to two years. Their results, published in Basic and Clinical Andrology, showed the gel to be 100% effective at preventing pregnancies in fertile—called “intact”—rhesus monkeys. The gel is a high molecular weight polymer developed in the US, formulated to work by occluding—or blocking—the vas deferens, which is a tiny muscular tube that carries sperm from the testicles to the penis.
Vasalgel was inspired by the Parsemus Foundation’s work on a polymer contraceptive called RISUG®, which is in advanced clinical trials in India; some of those men have been using RISUG® for over 15 years. However, in order to qualify for the study, men must be local, so wider clinical trial for men have not yet moved to the US or other countries.
The gel does not contain any hormones or deliver any pharmaceutical effects. First tested successfully in rabbits, Vasalgel™ is injected into the lumen, or main cavity of the vas deferens, forming a physical barrier through which the sperm cannot pass. Moreover, at least in rabbit subjects, the gel has been found to be reversible by flushing the gel out with a saline solution, successfully restoring sperm flow. Researchers are hoping this treatment might end up being an alternative to vasectomy, a surgery in which the tubes of the vas deferens from each testicle are cut, clamped or sealed, preventing sperm from reaching the penis. The sperm are then reabsorbed in the body. Vasectomies are a common procedure, but they are rarely reversible, and may bring buyer’s remorse for a percentage of men who change their minds and decide they do want children years later, after it’s possibly too late.
In comparing the Vasalgel procedure, VandeVoort says, “The rate of side effects was not significantly different than the vasectomy, and possibly even less than vasectomy.” She feels the side effects, such as swelling and irritation, had more to do with “the learning curve” of the researchers performing the surgery than the procedure itself. “The side effects we did have seemed to come earlier to the first few animals.”
Longevity is one of the key benefits of Vasalgel,™ as far as researchers can tell in animal models. “Some of the animals in the rabbit study covered two breeding seasons. We don’t know how long it will last but the fact is we’re into multiple year territory, which is a really good sign,” says Catherine VandeVoort, co-author of the study, a core scientist at the California National Primate Center, and a professor of obstetrics and gynecology at UC Davis.
VandeVoort and her team tested the gel in non-human primates, specifically rhesus monkeys, whose physiology is more similar to humans. VandeVoort says the study allowed the primate center to achieve one of their goals, as well. “We were trying to reduce the number of offspring we were producing, so having vasectomized animals was useful.”
Rhesus monkeys have a breeding season that ranges from September through May depending on whether they are kept indoors or outdoors. When kept indoors, researchers can breed animals in that time with success. “Outdoors it’s similar except most of the animals who will get pregnant fairly soon in the breeding season,” she says. Sixteen male monkeys were given the gel. Half of the monkeys were housed for at least one complete breeding season, and half for two complete breeding seasons with fertile females. There were no pregnancies.
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