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

Objective: 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.