The safety of popular osteoporosis drugs such as Merck’s Fosamax and Roche’s Boniva is under the spotlight in Europe after regulators launched a probe into a possible link between bisphosphonates and stress fractures of the femur.

The European Medicines Agency said Friday that its Committee for Medicinal Products for Human Use has kicked off a review to determine whether an increased risk of atypical stress fractures in osteoporosis patients taking bisphosphonate medicines is a class effect, following in the footsteps of US regulators which announced a similar move earlier this month.

Concerns over the safety of bisphosphonates were heightened by a recent study, published in the Journal of Bone and Mineral Research, which showed that their long-term use could indeed increase the risk of unusual fractures of the femur.

But the CHMP will now assess all available data - including published, non-clinical and clinical data and post-marketing reports - and their impact on the risk-benefit equation of these medicines to get a clearer picture, the Agency said.

Label change?

A warning of atypical stress fractures of the proximal femoral shaft was slapped onto product labels for alendronate (Merck’s Fosamax) following a review in Europe in 2008. But depending on the outcome of the current probe, all bisphosphonate drugs could be forced to carry strong warnings of the potential risk, or their use may even be restricted.

Merck is already facing a stream of lawsuits regarding stress fractures associated with Fosamax, which allege that the company did not adequately research its blockbuster or warn patients of the higher risk of thigh bone breaks, according to

And the news marks a further blow to the class of bisphosphonates in weeks, after a large-scale study by researchers in the UK reported earlier this month that five years’ use could double the risk of oesophageal cancer, although this did contrast with findings of a previous trial, published in the Journal of the American Association, which found no increased risk.