The US Food and Drug Administration has completed a safety review of Sanofi's heart drug Multaq which showed the heart drug increased the risk of serious cardiovascular events when used by patients in permanent atrial fibrillation. and has revised its label.

The agency has been looking at data from the French drugmaker from two trials, PALLAS (which was discontinued in July) and ATHENA, which provided the basis for the US approval of  Multaq (dronedarone) in July 2009 for the treatment of non-permanent AF. The FDA has added a new safety warning, notably one stating that the drug should not be prescribed to patients with AF who cannot or will not be converted into normal sinus rhythm (ie permanent AF), as it "doubles the rate of cardiovascular death, stroke, and heart failure in such patients".

The agency also notes that doctors should monitor heart rhythm at least once every three months. If the patient is in AF, Multaq should be stopped, the FDA says, adding that it is reviewing the risk evaluation and mitigation strategy for the treatment.

However the regulator stresses that Multaq provides a benefit for patients with non-permanent AF. Since approval through October 2011, some 1.3 million prescriptions have been dispensed for 278,000 patients.

The FDA's move comes as no great surprise and comes after its European counterparts restricted Multaq's use. In September, the European Medicines Agency said the drug should only be given after alternative treatment options have been considered.

Multaq was originally touted as a blockbuster but the FDA and EMA restrictions has probably put paid to that notion. In the third quarter, sales were up 52.2% but only to 66 million euros.