The researchers evaluated the prevalence of warfarin-related adverse drug interactions based on over 6,000 post-mortem cases on a Finnish toxicology database and the related death certificates.

They found that at least one interacting drug was present in a third of the 328 warfarin-positive cases; paracetamol was the most common, accounting for 49 per cent of that. The researchers say that when warfarin and paracetamol were detected simultaneously, the number of fatal bleeds was 4.6 and 2.7 times higher than with paracetamol or warfarin alone, respectively (P<0.05).

Marta Hildebrandt and Linda Hirst, pharmacists with a special interest in anticoagulation at Wilsden Medical Practice, Bradford, said that paracetamol does increase INR and that they usually advocate only small, occasional doses. “Paracetamol is often considered a safer option since there is no stomach irritation or effect on the platelets,” they said. But the risk of an interaction should not be underestimated, they added.