A new trial shows promise for a non-hormonal gel as an alternative to vasectomy.
Almost half of all pregnancies are unintended, according to the latest statistics from the Centers for Disease Control and Prevention (CDC).
While women have traditionally had a wide range of contraceptives available to them, the medical research community has only recently taken an interest in developing male contraceptives.
In 2016, the male non-hormonal contraceptive gel Vasalgel was successfully tested in rabbits, showing promise as a long-term contraceptive for males.
Vasalgel is a high molecular weight polymer that could work as a potentially reversible alternative to vasectomies.
In the new trial, researchers - led by Dr. Catherine VandeVoort, from the California National Primate Research Centre (CNPRC) - tested the drug in primates. The findings were published in the journal Basic and Clinical Andrology.
How Vasalgel works in monkeys
Vasalgel is injected into the so-called vas deferens - the thick-walled tube that transports sperm from the testicles to the urethra.
Inside the cavity of the vas deferens, the gel forms a barrier that puts a stop to the movement of the sperm.
In this study, Dr. VandeVoort selected a test group of 16 adult male rhesus monkeys housed at the CNPRC, and a control group of 16 age-matched monkeys that had been previously vasectomized.
The animals were sedated with Ketamine for the duration of the surgery and administered approximately 100 microliters of Vasalgel with the help of a syringe through a small incision.
This dose of Vasalgel formed a barrier of approximately 2 centimeters in length inside the vas deferens. The animals were administered analgesics postoperatively to help with the pain, and were monitored daily for 7 days after the surgery.
After that, researchers returned the monkeys to their normal group housing, where they cohabitated with females for a minimum of one breeding season of around 6 months. Seven males lived almost continuously with females for 2 years.
The paternity of all the offspring was tested via blood samples and genetic testing. The researchers report that the treated males had no conceptions after the Vasalgel injections.
In similar housing conditions, sexually mature females are expected to have a pregnancy rate of 80 percent per breeding season.
Vasalgel is 'safe' and produces 'fewer complications' than vasectomies
The authors report a few minor complications, similar to those commonly associated with traditional vasectomies. One monkey in the group developed sperm granuloma after the injection. This complication - consisting of a lumpy buildup of sperm in the vas deferens - occurs in around 60 percent of human vasectomy cases, according to the authors. As they explain, there are typically no serious side effects resulting from sperm granuloma.
The rate of sperm granuloma in vasectomized male rhesus monkeys is typically around 15 percent, whereas 1 in 32 - as was the case in this study - amounts to little over 3 percent.
In the age-matched control group, 5 out of 16 (or over 32 percent) of the vasectomized male rhesus monkeys developed a form of sperm granuloma.
"Our research shows that Vasalgel placement into the vas deferens produces reliable contraception in mature male rhesus monkeys as shown by the lack of pregnancies in reproductively viable females with which the males were housed. Importantly, we show that the method of Vasalgel placement is safe and produced fewer complications than usually occur with a vasectomy."
Dr. Catherine VandeVoort
Dr. VandeVoort and her colleagues recommend that future research investigates the reversibility of Vasalgel in monkeys before the gel can become a valid alternative to vasectomy in human males.
"Vasalgel shows real promise as an alternative to vasectomy because research in rabbits has previously shown the product to be reversible," she adds. "Although it is possible to reverse a vasectomy, it is a technically challenging procedure and patients often have very low rates of fertility following reversal."