The influence of oseltamivir treatment on the risk of stroke after influenza infection.

OBJECTIVES It was the aim of this study to examine the influence of the antiviral medication oseltamivir on stroke and transient ischemic attack (TIA) in adults diagnosed with influenza. METHODS This retrospective cohort study used medical and pharmaceutical claims data from May 2000 to September 2006 from an administrative claims database. Episodes of stroke/TIA in the 6 months after influenza in adults (aged > or =18 years) prescribed oseltamivir within 1 day before or 2 days after influenza diagnosis (oseltamivir cohort), and adults prescribed no antivirals (comparison cohort) were compared using multivariate analyses adjusted for demographic and clinical risk factors. RESULTS The oseltamivir cohort comprised 49,238 patients and the comparison cohort 102,692 patients. Oseltamivir was associated with a 28% reduction in risk of stroke/TIA in the 6 months after influenza [hazard ratio (HR) 0.72; 95% CI 0.62-0.82] and with significant reductions after 1 and 3 months. In patients <65 years of age, there was a 34% risk reduction with oseltamivir after 6 months (HR 0.66; 95% CI 0.56-0.77) and also significant reductions after 1 and 3 months. In those aged > or =65 years, there was a 51% reduction in risk after 1 month (HR 0.49; 95% CI 0.27-0.91). CONCLUSIONS Prescription of oseltamivir for influenza is associated with a reduced risk of stroke/TIA.