Cost-Effectiveness Analysis of Inhaled Zanamivir in the Treatment of Influenza A and B in High-Risk Patients

Objective: To evaluate the cost effectiveness of zanamivir 10mg twice daily for 5 days in the treatment of influenza in high-risk patients. Design: Bootstrap cost-effectiveness analysis incorporating within-trial analysis of pooled patient-level cost and effect data. Setting: UK unit costs and utilities applied to high-risk patients drawn from 6 multinational clinical trials. Patients: A total of 154 zanamivir and 167 placebo high-risk patients were included in the analysis. Main outcome measures: Cost per day of normal activities; cost per symptom-free day; cost per complication averted; cost per quality-adjusted life-year (QALY). Results: The mean benefit was estimated to be 2.5 days [95% confidence interval (CI): 0.68 to 4.27] of normal activities gained; 2.0 (95% CI: 0.56 to 3.51) symptom-free days; and a 9% reduction in complications (95% CI: 0 to 18%). Excluding the effect of rare hospitalisation costs, the cost (1999 values) of gaining a day of normal activities was Lstg 9.50 (95% CI: Lstg 5 to Lstg 39); cost per symptom-free day was Lstg 11.56 (95% CI: Lstg 6 to Lstg 43); cost per complication averted was Lstg 262 (95% CI: Lstg 90 to Lstg 1574). Influenza was estimated to reduce utility by 0.883 per day, demonstrating the debilitating effect of the disease. Extrapolating a day of normal activities to a standard utility measure resulted in a cost per QALY of Lstg 3900 excluding inpatient costs (Lstg 7490 including inpatient costs). Cost-effectiveness acceptability curves demonstrated 90% certainty that zanamivir would be cost effective at Lstg 8000 per QALY. Conclusions: Significant health benefits can be obtained with zanamivir treatment in high-risk patients. The cost per QALY for zanamivir in these patients compares well with that of other commonly used pharmacological interventions.