US regulators have issued an “early communication” about an ongoing safety review of all bisphosphonates after they received postmarketing reports of atrial fibrillation in patients who received such treatments for osteoporosis.

The US Food and Drug Administration said that it initiated its review after the May 3, 2007 issue of The New England Journal of Medicine suggested that two different studies in older women with osteoporosis of Novartis’ Reclast (zoledronic acid) and Merck & Co’s Fosamax (alendronate) could increase the risk of atrial fibrillation. The other bisphosphonates under review are Procter & Gamble's Didronel (etidronate), Roche and GlaxoSmithKline's Boniva (ibandronate), Novartis' Aredia (pamidronate); Sanofi-Aventis and P&G’s Actonel (risedronate), plus Sanofi’s Skelid (tiludronate).

The agency has recommended that healthcare providers should not alter their prescribing practices for bisphosphonates at the moment, because it is still unclear how the data for serious atrial fibrillation should be interpreted. The FDA added that it has requested additional information to "further evaluate the risk of atrial fibrillation in patients who take bisphosphonates," and expects its review to take up to 12 months to complete.

Merck said that “a true association between atrial fibrillation and treatment with Fosamax,” the market leader with second-quarter sales of $742 million, was considered unlikely by both independent study investigators and the firm itself.