New Evidence for Blood Clots With the Pill. Will Canadian Ob/Gyn Group Revise its Guidelines on Drospirenone?

April 26, 2011

By Kate Johnson

The Society of Obstetricians and Gynaecologists of Canada (SOGC) has a chance to redeem itself and make good on its controversial new contraceptive guidelines.

As I wrote in my last post, the guidelines are tainted with undisclosed conflicts of interest, calling their recommendations into question.

Now, two new studies in the British Medical Journal have made the guidelines redundant – presenting the SOGC with a rare opportunity to correct its mistakes (BMJ 2011;340:d2151 and BMJ 2011;340:d2139).

If it rises to this challenge, the SOGC will get a much-needed second chance to fulfill its role in furnishing Canadian physicians and their patients with some solid recommendations about safe, reliable oral contraceptive options.

For months the SOGC has been warning its members and the public about the potential for a “pill scare”, a mass abandonment of the top-selling drospirenone-containing oral contraceptives Yaz and Yasmin, due to fears of blood clots, or venous thromboembolisms (VTEs).

Mounting lawsuits against Bayer, the manufacturer of the pills, claim the products carry a higher risk of VTEs than older levonorgestrel-containing pills.

The SOGC, concerned about the bad press, says it fears a repeat of the 1995 British pill scare, which was triggered by similar VTE concerns in levonorgestrel-containing pills. The scare prompted mass discontinuations of the pills, a surge in unplanned pregnancies and abortions, and a 25% increase in the national birth rate (Human Repro 1997; 12 (12): 2595-2598).

Dismissing current concerns about Yaz and Yasmin as “stimulated reporting” – “the phenomena whereby media attention stimulates physicians and patients to report adverse events”,  the SOGC issued guidelines and a statement insisting the  Bayer products are just as safe as other oral contraceptives and even “offer additional benefits to women with acne and hirsutism”.

But, as I wrote previously, the group’s opinion seems largely influenced by the manufacturer.

Medical authorities have been less definitive than the SOGC on this issue. Prior to this new evidence, the U.S. Food and Drug Administration leaned, somewhat obscurely, towards the safety of the products, while the European Medicines Agency (EMA) and the British Medicines and Healthcare products Regulatory Agency (MHRA) concluded that the risks may have been “slightly higher than previously estimated”.

Prescrire, an independent European journal concluded that compared to older pills, those containing drospirenone conferred a “high risk of thrombosis” and were “not the best choice”.  (Rev Prescrire 2011; 113 p.43-45).

But now, the two new studies add fuel to those safety concerns – showing drospirenone-containing pills carry a 2.7-fold and 3-fold increased risk of VTE compared to levonorgestrel-containing pills.

Although “the data are inconclusive”, due to some weaknesses such as small numbers and missing information, “it seems sensible to prescribe an oral contraceptive with a  well known favourable safety profile (one that contains levonorgestrel) unless there is persistent reason to use another type,” concluded Nick Dunn, MD, senior lecturer at the University of Southampton School of Medicine, in England, in an accompanying editorial (BMJ2011;342:d2519).

In a predictable response to the new evidence, Bayer has issued a statement saying the new studies are flawed – an echo of its similar criticisms about previous studies. It says the safety of its products is based on solid evidence from two self-sponsored studies (Contraception. 2007 May;75(5):344-54 and Obstet Gynecol. 2007 Sep;110(3):587-93), and that two earlier studies which first suggested an increased VTE risk were also flawed (BMJ 2009;339:b2890 and BMJ 2009;339:b292).

To date, SOGC’s  statements and guidelines have mirrored Bayer’s analysis – which is not surprising given the society’s reliance on the company for scientific analysis and interpretation.

With it’s second chance to avert a pill scare, let’s hope the SOGC will venture beyond its industry reference points, subject the new studies to unbiased analysis, acknowledge that there may possibly be as much as a 3-fold increased risk with drospirenone-containing pills, but that in absolute terms that risk still remains small.

If the new evidence is confirmed, a 2.7-fold to 3-fold increased risk is still small –  meaning out of 100,000 women taking drospirenone-containing contraceptives in one year,  23 to 30 would have an VTE, compared to between 9 and 12.5 among those taking levonorgestrel-containing pills.

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