By Nathan Seppa
June 27, 2012
Guys might someday have a birth-control option that rivals the pill. Two gels applied to the skin deliver hormones that knock down a man’s sperm count, acting as a male contraceptive, researchers reported June 25 at the Endocrine Society’s annual meeting.
While women have had access to hormone-based contraceptives for decades, men have had few alternatives beyond condoms and vasectomies. In the new trial, scientists randomly assigned 99 men in the Seattle and Los Angeles areas to apply two unlabeled gels to their skin daily. Some men got gels containing testosterone and Nestorone, a synthetic hormone similar to progestin. Others got a testosterone gel and a placebo.
In all, 56 of the men completed at least 20 weeks of the regimen. By the end, 89 percent of men who got the dual hormone treatment saw their sperm counts plummet from about 15 million per cubic milliliter of ejaculate to less than 1 million. What’s more, a majority of those men made no detectable sperm at all, the researchers found.
“Less than 1 million is an arbitrary line, but it’s a threshold that we say is compatible with effective contraception,” said study coauthor Christina Wang, a physician at UCLA. “There was very effective suppression of spermatogenesis.”
About 23 percent of men getting testosterone plus placebo saw their sperm counts drop below 1 million in response to that one-hormone treatment.
“This is an interesting and important clinical study showing that a transdermal male contraceptive may be possible in the future,” says James Dalton, chief scientific officer at GTx Inc., a biopharmaceutical firm in Memphis, Tenn. “The use of transdermal gels for male contraception is a potentially meaningful advance compared to the prior approaches, which required intramuscular injection.” This approach “clearly deserves further investigation,” he said, noting that the research would need to improve on the treatment’s 89 percent effectiveness rate.
The Nestorone-plus-testosterone treatment inhibits certain activities in the brain’s hypothalamus and in the pituitary gland that regulate sperm manufacture by the testes, largely shutting it down, Wang said. But the treatment is reversible: In all the men, sperm counts returned to normal by about 12 weeks of stopping the medications.
One-fifth of participants reported developing some acne during the study, apparently from the testosterone. And while 43 men left the study early, they did so mainly by failing to return for all the numerous blood tests required in the study protocol, not because of side effects, Wang said.
Large-scale testing of a single, combined gel — possibly with lower doses of testosterone — will be needed to get regulatory approval for the drug combination. The National Institute of Child Health and Human Development and the Population Council provided support for this study.
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