When combined and applied to the skin, testosterone and a synthetic progestin provided a successful method for suppressing sperm concentration, with minimal adverse effects.

In the past, combinations of testosterone and progestin injections with pills; implants with injections; or two different injections or implants enhanced the suppression of sperm production as a method of contraception. Injections and implants require a provider to administer the hormones.

“Our purpose was to develop a user friendly male contraceptive,” Christina Wang, MD, researcher and professor at the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, said during a presentation. “We showed the [synthetic progestin] gel was very effective in suppressing spermatogenesis in combination with testosterone gel.”

Wang and colleagues at LA BioMed and the University of Washington aimed to determine the effectiveness of testosterone gel alone or combined with Nestorone (NES) — a non-androgenic and non-estrogenic progestin in gel form being developed by the Population Council — through a randomized, double blind, comparator clinical trial completed at two academic medical centers.

“Nestorone was chosen because it’s a pure progestin,” Wang said.

The patient population was composed of 99 healthy men who were randomly assigned to one of three treatment groups applying daily transdermal gels: testosterone 10 g plus placebo (n=32); testosterone 10 g plus NES 8 mg (n=33); testosterone 10 g plus NES 12 mg (n=34).

Researchers analyzed 56 patients who completed at least 20 weeks of treatment. The percentage of men with sperm concentration of less than 1 million/mL was significantly higher for testosterone plus NES 8 mg (89%, P<.0001) and testosterone plus NES 12 mg (88%, P<.0002) vs. the testosterone plus placebo group (23%).

Additionally, data conveyed that significantly more patients became azoospermic in the testosterone plus NES 8 mg (78%, P<.001) and testosterone plus NES 12 mg (69%, P<.008) groups vs. testosterone plus placebo (23%).

All participants recovered to a sperm concentration of more than 15 million/mL during the recovery period. Adverse effects were minimal in all groups, with acne being the most common (21%).

“We can achieve effective suppression of sperm concentration, and after we test the combination of testosterone and Nestorone formulated into one gel and show efficacy, we will proceed to a phase 3 contraceptive efficacy study supported by the National Institute of Child Health and Human Development,” Wang said.

Source: Endocrine Today.