Cerebral Haemorrhage Induced by Warfarin - the Influence of Drug-drug Interactions

Purpose: To evaluate the frequency, severity and preventability of warfarin-induced cerebral haemorrhages due to warfarin and warfarin-drug interactions in patients living in the county of Ostergötland, Sweden.

Methods: All patients with a diagnosed cerebral haemorrhage at three hospitals during the period 2000-2002 were identified. Medical records were studied retrospectively to evaluate whether warfarin and warfarin-drug interactions could have caused the cerebral haemorrhage. The proportion of possibly avoidable cases due to drug interactions was estimated.

Results: Among 593 patients with cerebral haemorrhage, 59 (10%) were assessed as related to warfarin treatment. This imply an incidence of 1.7/100,000 treatment years. Of the 59 cases, 26 (44%) had a fatal outcome, compared to 136 (25%) among the non-warfarin patients (p < 0.01). A warfarin-drug interaction could have contributed to the haemorrhage in 24 (41%) of the warfarin patients and in 7 of these (12%) the bleeding complication was considered being possible to avoid.

Conclusions: Warfarin-induced cerebral haemorrhages are a major clinical problem with a high fatality rate. Almost half of the cases was related to a warfarin-drug interaction. A significant proportion of warfarin-related cerebral haemorrhages might have been prevented if greater caution had been taken when prescribing drugs known to interact with warfarin.