The widely used anti-osteoporosis drug, Fosamax, has received more bad news, with publication of a new study suggesting in some people it may cause fractures, rather than prevent them.

A small study published by doctors in the United States last month suggested long-term use of the drug may be associated with a rare new kind of leg fracture, which can see the upper thigh bone snap after only minimal trauma. The same doctors published a letter in the New England Journal of Medicine in March saying there was a “potential link” between the drug and these rare fractures of the thigh bone.

Last year, another small study from Singapore came to a similar tentative conclusion about Fosamax. The theory is for some people, long-term use can weaken bones like the thigh bone, making them break more easily, rather than strengthening them against fractures.

Importantly these studies are extremely small, and more suggestive than conclusive, with the authors of the new US study endorsing Fosamax, while at the same time warning of its potential new problem.

Big trials of the drug involving many thousands of women — many funded by the manufacturer Merck Sharpe & Dohme — have shown the drug can, on average, reduce fracture risk, particularly for people at high risk to start with. Fosamax has been heavily marketed around the world for the past decade, becoming a major source of profit for Merck. Yet with so many women now taking the drug, there is growing concern about rare, but potentially debilitating side effects.

The most recent official prescribing information about Fosamax, issued two months ago, actually includes mention of these new “atypical” fractures. It also notes the drug can cause “severe” ulceration of the oesophagus, especially if not taken properly, and warns about “osteonecrosis of the jaw”, more commonly known as jaw death. In this very rare side effect, commonly associated with dental work, a wound does not heal and the bone of the jaw becomes exposed. According to the US Food and Drug Administration, the class of drugs to which Fosamax belongs can also cause the possibility, in rare cases, of “severe and sometimes incapacitating bone, joint, and/or muscle pain.”

In a statement sent to Crikey yesterday about the new study, Merck Sharpe & Dohme pointed out there were a large number of people with osteoporosis, the benefits of its drug were well established, and that the US study had just 70 people, compared to the 17,000 people who had participated in trials.

“The decision to treat a patient with any medicine” said the company, “should be made between the patient and their doctor, after evaluating all the relevant risks and benefits.”

Ray Moynihan is co-author of Ten Questions You Must Ask Your Doctor, which will be published next week by Allen & Unwin, and contains a section on osteoporosis.

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