Clot risk tied to birth control patch

WASHINGTON – Women using the increasingly popular birth control patch might face double the risk of blood clots compared with women taking contraceptive pills, but more investigation is needed to see if the preliminary findings are valid, federal regulators said Friday.

“We’re not sure what this means clinically, but it’s information that people need to know about,” said Dr. Daniel Shames, who heads 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,” Shames added.

Blood clots usually form in the legs, and sometimes in the lungs. They 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 is cooperating with the FDA in the ongoing scientific investigation. Sales of the patch totaled more than $400 million in 2004, according to DrugTopics.com, an industry Web site.

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. While contraceptive pills have to be taken daily, a woman can wear one patch for seven days.

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.

“Because it is absorbed directly through the blood as opposed to a pill taken by mouth … the total exposure is more,” said Shames.

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 a two-fold increase in the risk of blood clots in the legs and lungs for women using the patch. Complete data from the second study have not been released publicly.