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Patients with atrial fibrillation (AF) may be at an increased risk of stroke during the first 30 days of treatment with warfarin, according to an analysis of 70,766 AF patients in a UK primary care database.

The study, funded by Bristol-Myers Squibb and Pfizer, followed patients for up to 16 years until an ischaemic stroke, death, end-of-practice registration, or end of the study. Over this time, 5,519 patients experienced a stroke – equivalent to approximately 2 per cent a year.

During the first 30 days after starting warfarin, the risk of ischaemic stroke was 71 per cent higher in patients taking warfarin compared to patients with AF not taking anticoagulants.

The highest stroke risk was in the first week of treatment and peaked on the third day after starting warfarin (2.3-fold increase). Patients with a history of ischaemic stroke were 2.5-fold more likely to experience a stroke during the first 30 days. However, 31 to 90 days after starting warfarin, stroke risk declined by 50 per cent and by 45 per cent after 90 days.

“While these findings need to be confirmed in other settings, it would be imperative to also investigate whether the newer popular anticoagulants also carry this early risk,” says senior author Samy Suissa, James McGill professor of epidemiology, biostatistics and medicine at McGill University, Montreal.

In the meantime, he suggests considering a bridging strategy using heparin at the start of warfarin treatment to potentially reduce the increased risk in the first 30 days.