Less than a month after the European Medicines Agency backed the safety of Boehringer Ingelheim's Pradaxa despite an increasing number of fatal cases of bleeding in patients treated with the anticoagulant, regulators in the USA have launched their own review.

The US Food and Drug Administration says it is evaluating post-marketing reports of serious bleeding events in patients taking Pradaxa (dabigatran), which is used to reduce the risk of stroke in patients with non-valvular atrial fibrillation, the most common type of heart rhythm abnormality. The agency did not give any specific figures but said it is analysing the cases to determine whether the reports of bleeding in patients taking Pradaxa are occurring more commonly than would be expected.

The FDA said that it is a fairly complicated process. Noting that for non-valvular AF, the main alternative to Pradaxa is warfarin but because the latter has been marketed for over 50 years and is well-known to cause bleeding, patients are not likely to report it. The agency adds that "a simple comparison between Pradaxa and warfarin with respect to the numbers of post-marketing reports of bleeding is of limited value".

The FDA also stressed that it continues to believe Pradaxa "provides an important health benefit when used as directed". It has also told patients with AF not to stop taking the drug without talking to their doctor.

Boehringer responded by saying that "the clinical effectiveness and favourable safety profile of Pradaxa is positive and remains unchanged in light of recent reports about fatal cases of bleeding in the media". From approval in October 2010 to August 2011, some 1.1 million Pradaxa prescriptions were dispensed and 371,000 patients received the drug from US outpatient retail pharmacies.

Last month, the EMA reported 256 cases of serious bleeding resulting in death associated with the use of Pradaxa (21 of which were reported in the European Union). It said that recent label changes "adequately manage the risk of bleeding".