WASHINGTON -- Women using the increasingly popular birth control patch could face double the risk of blood clots as women taking contraceptive pills, but more investigation is needed to see whether those preliminary findings are valid, federal regulators said yesterday.
"We're not sure what this means clinically, but it's information that people need to know about," said Dr. Daniel Shames, head of the Food and Drug Administration division that evaluates contraceptives.
"At this time, we do not plan on taking any specific regulatory action based on these preliminary results."
Blood clots can form in the legs or lungs and can travel to the heart or the brain, causing heart attacks and strokes. But the overall risk of blood clots among women taking birth control pills is low, about three to five cases for every 10,000 women treated for a year.
Manufacturer Ortho-McNeil Pharmaceutical Inc. said it was cooperating with the FDA in the scientific investigation. Sales of the patch totaled more than $400 million in 2004, according to DrugTopics.com, an industry Web site. Ortho-McNeil, a division of Johnson & Johnson, sponsored the research that is raising concern.
Marketed as Ortho Evra, the birth control patch has been used by more than 4 million women since it was approved by the FDA in late 2001. It works by releasing estrogen directly into the bloodstream through vessels near the surface of the skin.
Because estrogen can promote the formation of blood clots, women taking any hormonal contraceptive run the risk of such side effects.
But with the patch, the total level of estrogen exposure is 60 percent higher than with a typical birth control pill, according to the FDA.
The FDA issued a warning in November about the higher levels of estrogen with the patch. The latest worries come after two safety studies commissioned by the manufacturer produced seemingly contradictory results.
A recently published study by the Boston Collaborative Drug Surveillance Program found no higher risk of blood clots among women using the patch than among those taking the standard dose of birth control pills.
But preliminary findings from the second study, by i3 Drug Safety, found that the risk of blood clots in the legs and lungs doubled for women using the patch. Complete data from the second study have not been publicly released.
Both studies used insurance claims data to track the experiences of tens of thousands of women using the medications. Researchers are also looking into whether women using the patch face a higher risk of heart attacks and strokes.
Last year, an Associated Press analysis of FDA reports of serious drug side effects indicated that women using the patch faced a three times higher risk of dying or suffering a blood clot than did those taking birth control pills.
Some critics of the agency say the potential for harm should have been clear in clinical trials before the patch was approved.
"It is no more effective than the pill and has a higher risk because it delivers significantly more estrogen," said Dr. Sidney Wolfe, of the advocacy group Public Citizen.
Susan Wood, a former head of the FDA women's health office, said the agency "still doesn't have enough data to make a call" on the safety of the patch.
Ricardo Alonso-Zaldivar writes for the Los Angeles Times.