Oseltamivir once or twice daily safely prevented influenza

Abstract

Design Two G week randomised (allocation concealed), blinded (clinicians and patients), placebo controlled trials during influenza season. Setting 3 centres in Virginia, 2 in Texas, and 1 in Kansas, USA. Participants 1562 people who were 18 to 65 years of age (mean age 35 y, 63% women) and were recruited by advertisement. Exclusion criteria were influenza vaccination in the previous year, meeting > 1 criterion for influenza immunisation according to current (US) guidelines, acute respirator)' illness with fever in the previous week, pregnancy, or potential for pregnancy. 1559 participants took & 1 dose of die assigned study medication and were included in the analysis (intention to treat). Intervention Participants were allocated to oral oseltamivir, 75 mg once (n = 520) or twice (n = 520) daily, or to placebo (n = 519) for 6 weeks, beginning when influenza virus activity increased at the local study sites. Main outcome measures Laboratory confirmed influenza-like illness (laboratory confirmation UTIS culture of influenza virus within 2 d of the onset of influenza symptoms or antibody titer on haemagglutination inhibition testing &4 times the baseline titer or both). Adverse events were also assessed. Main results Fewer patients receiving oscltamivir developed laboratory confirmed influenza than did patients receiving placebo (once daily p<0.001, twice daily p = 0.001) (table). Rates of influenza were higher at the 3 Virginia sites than at the Texas and Kansas sites. Oseltamivir reduced influenza in Virginia (protective efficacy 82%, 95% CI 60% to 93%; p < 0.001) but showed no significant reduction in Texas and Kansas (protective efficacy 50%, CI -23% to 93%; p = 0.39). Nausea and vomiting were reported by more oseltamivir recipients than placebo recipients but did not contribute to discontinuation of treatment (table). Conclusion Oseltamivir once or twice daily was effective and safe in preventing influenza.