Trials focus on hormonal birth control for men
■ While the potential for a male pill has long been recognized, biological factors add to the challenge of making it happen.
By Susan J. Landers — Posted March 8, 2004
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Washington -- Could clinical trials of a male hormonal contraceptive signal the start of a new era in birth control? It's possible, but don't toss the condoms out just yet, say those in the know.
"My understanding is that it will be at least five to 10 years before there is going to be any hormonal male contraceptive methods," said Vanessa Cullins, MD, vice president for medical affairs at the Planned Parenthood Federation of America.
"The issue really revolves around the continuous production of sperm by men," she said. While an effective hormonal birth control pill for women need only address a single fertile period in one month, it could take four months or more to reduce the vast numbers of sperm produced to a point where pregnancy is unlikely.
Most male hormones are not orally active, leading to the need for injectable or implantable formulas, noted Doug Colvard, PhD, associate director for CONRAD, a Virginia organization established by the Eastern Virginia Medical School and the U.S. Agency for International Development to fund reproductive health and HIV prevention efforts in the United States and abroad.
The potential for a hormonal male contraceptive has been recognized for decades, but options for men interested in assuming the responsibility for contraception have remained the same -- condoms and vasectomy.
Despite this limited choice, men account for one-third of all contraceptive use in the United States and worldwide, says a January Institute of Medicine report on contraception, "New Frontiers in Contraceptive Research: A Blueprint for Action."
This fact negates a long-held assumption that men don't want a role in birth control and that women would be unable to trust a partner to use an effective method.
"I think we can get rid of the misconception of men not wanting to use contraception and women not trusting men," said Dr. Cullins. "This should not be the basis for deciding whether or not to develop male contraception methods."
The reversibility of hormonal birth control is one of its attractions, says the IOM report. About 3,000 men have participated in hormonal contraception research over the last 20 years, and none of them has failed to return their sperm counts to normal levels after stopping the hormone use, says the report.
Research has focused on the use of high doses of testosterone to suppress sperm levels. However, adding the female hormone progestin seemed to lessen the amount of testosterone needed to trick the body into thinking the testes had produced sufficient testosterone and cause sperm production to stop.
High-dose testosterone use is accompanied by some side effects. Among them are increased muscle mass and weight, which were not viewed as negatives; but other side effects include a decrease in high-density lipoprotein levels in about 10% of men and a decrease in testicular size in about 25%, said the IOM report.
Researchers are examining the use of injected or implanted testosterone alone, testosterone plus progestin and testosterone plus a hormone antagonist that acts on the hypothalamus.
Schering AG Germany and the Dutch branch of the pharmaceutical company Organon International Inc. began a double-blind, randomized trial of an injectable long-acting testosterone and an implantable progestogen in 350 men in late January. The trial is being conducted at 14 European sites and is expected to conclude by December 2005.
A year-long Australian trial of the hormones concluded last fall with no pregnancies among the 55 couples enrolled, researchers reported. "It was a very effective regimen at suppressing sperm production and inducing infertility," said Dr. Colvard. CONRAD helped fund the trial.
While the trial demonstrated efficacy, there were some drawbacks, he said. For example, the implanted testosterone pellets occasionally extruded from the skin.
Despite this research interest, no male hormonal contraceptive has been submitted for FDA review or approved for use in other countries.
However, a large trial in China, funded by the World Health Organization, is likely to conclude in about two years, and it is possible that approval could be granted for male testosterone use as a birth control method there.