Background It is uncertain whether thrombolytic therapy is safe in patients with acute ischaemic stroke who are treated with warfarin and have a subtherapeutic international normalised ratio (INR) at stroke onset.

Methods The authors performed a systematic review of the literature and included studies that assessed the relation between prior warfarin use with subtherapeutic INR and outcome after intravenous or intra-arterial thrombolytic therapy in acute ischaemic stroke. Outcome measures were symptomatic intracranial haemorrhage (SICH), modified Rankin scale score 0–2 and mortality. Second, the authors performed a meta-analysis of the included studies.

Results Seven studies with 3631 patients were included. 240 (6.6%) patients used warfarin before stroke onset. The risk of SICH was increased in the warfarin group (OR 2.6; 95% CI 1.1 to 5.9. p=0.02). There was no significant difference, however, in functional outcome (OR 0.9; 95% CI 0.6 to 1.2, p=0.32) or death from all causes (OR 1.2; 95% CI 0.9 to 1.8).

Discussion The risk of SICH after thrombolytic therapy is increased in patients using warfarin with subtherapeutic INR levels. The authors found no evidence of an increase in death from all causes or worsening of functional outcome in warfarin treated patients.