Doctors in the UK have been alerted to a small batch of cases where patients taking Sanofi's clopidogrel have developed the rare autoimmune disease acquired haemophilia.

In a letter to healthcare professionals, the French drugmaker reported a small number of cases of acquired haemophilia in patients taking the drug (marketed as Plavix and Clopidogrel Zentiva), despite having no prior history of abnormal coagulation.

Eleven case reports of acquired haemophilia A and one of haemophilia B associated with clopidogrel treatment have been transmitted to Sanofi or published in the literature post launch, it said.

Onset of the condition ranged from a few days up to four months after starting treatment, and two cases were life-threatening (though non-fatal).

Product information is being updated with information on this risk, but Mark Toms, Medical Director at Sanofi UK/Ireland, stressed that, given the small number of reports in a huge number of patients taking the drug (153 million worldwide), regulators consider its benefit-risk ratio unchanged.

Nevertheless, doctors should promptly recognise the development of acquired haemophilia to minimise the time the patient is at risk from bleeding, and treatment with clopidogrel should be discontinued in such circumstances, he stressed.