Skin reactions in patients with influenza treated with oseltamivir: a retrospective cohort study.

Oseltamivir phosphate is an FDA-approved treatment for influenza that has been available for prescription use in the USA since 1999. The present report describes findings from a post-marketing safety study of skin reactions associated with oseltamivir use. All patients in the claims-derived Ingenix Research Database with a physician diagnosis of influenza and/or a dispensing of oseltamivir between 1 December 1999 and 31 March 2002 were identified. Cohort eligibility criteria included minimum baseline enrolment duration of 3 months, age of at least 1 year and no influenza vaccination on the date of influenza diagnosis or oseltamivir dispensing. Patients were classified into two primary cohorts, influenza diagnosis and oseltamivir dispensing on the same day, and influenza diagnosis but no oseltamivir at any time, and a cohort included for secondary analyses comprising patients who received an oseltamivir dispensing without an influenza diagnosis on the same day. Outcomes included general skin reactions and several specific skin reactions. Events occurring during the 30 days following the date of influenza diagnosis or oseltamivir dispensing were examined using Cox proportional hazards models. Model covariates included age, use of another influenza drug, month and year of index date, and use of antitussives. Adjusted rate ratios for the general class of skin reactions among the primary cohort of oseltamivir users versus non-users were 1.05 (95% CI: 0.88-1.24) for incident cases and 0.98 (95% CI: 0.77-1.24) among patients with a history of a skin reaction. Similar results were seen for the other skin reaction categories, and secondary analyses investigating the oseltamivir users without influenza revealed no elevation in risk. It is concluded that oseltamivir use does not appear to be associated with an increased risk of skin reactions.