A new
study of 1.3 million Danish women over nine years adds to the evidence that
some newer birth-control pills, including the best-seller Yaz, have a higher
risk of causing potentially dangerous blood clots.
Newer
pills containing drospirenone, a synthetic hormone, were linked to a six-fold
increase in the risk of venous thromboembolism, which is the formation of clots
in the lower leg or thigh that can break loose and travel to the lungs.
That
risk was compared with a three-fold increase in women using older
contraceptives containing the synthetic hormone levonorgestrel. The studywas published Tuesday on the Web site
of BMJ, formerly known as the British Medical Journal.
A BMJ
editorial added, “It is crucial, however, not to exaggerate the risk — oral
contraceptives are remarkably safe and may confer important long-term benefits
in relation to cancer and mortality.”
The
Food and Drug Administration is already studying the possible increased risk of blood
clots with pills containing the drospirenone. The F.D.A. says its preliminary
results suggest a 1.5-fold increased risk compared with other hormonal
contraceptives, to about 10 women in 10,000 from 6 women in 10,000.
Studies
have differed, though. Some found no increased risk among women taking the
newer pills. The F.D.A. has scheduled a joint meeting of two advisory
committees on Dec. 8 to review the risks and benefits.
Bayer,
the German drug company that makes Yaz and the related product Yasmin, has said
the two have similar clot risks to other combination birth control pills,
including levonorgestrel. The company updated its labels last year with that
indication.
The new
study, sought by the European Medicines Agency, challenges that finding.
Bayer,
in a brief statement Wednesday, said it is “currently evaluating this
publication and cannot comment at this time.”
Bayer
also said its clinical data from more than 15 years supports the company’s
assessment that its hormonal birth control products are safe and effective when
used as indicated and that the risk of venous thromboembolism is similar to
that from taking any other low-dose estrogen product studied.
Thousands
of women have sued Bayer, contending that they have suffered injuries from
taking Yaz or Yasmin. Bayer introduced Yasmin in 2001 and Yaz in 2006. Yaz
contains the same amount of drospirenone but a smaller amount of
ethinylestradiol, a synthetic estrogen commonly paired with progestins in birth
control pills.
The
Danish study found essentially no difference in the risk of venous
thromboembolism between Yaz and Yasmin, and in both cases, about double that of
some other hormonal birth control pills.
Some of
the numbers were small, though. The study found 23 reported events of venous
thromboembolism in the Yaz group, confirming 16 of them with medical records,
compared with 78 reported events, confirming 57 of them, for users of older
levonorgestrel. The latter group was more than four times larger than the Yaz
group. That left levonorgestrel with more certainty about a relative risk of
the clot of two to four times that of nonusers, while Yaz had a wider range of
risk, four to 11 times that of nonusers, within statistical significance, the
study said.
The
researchers estimated 2,000 women would need to change birth control pills to
prevent one incident of venous thromboembolism in a year.
Yaz has been marketed and F.D.A. approved
for quality of life treatment for acne and severe premenstrual symptoms, in
addition to birth control benefits. The drugs have had worldwide sales of $1.47
billion last year.
Yaz sales in the United States declined earlier this year, the
company said, blaming generic competition.
