Cost Estimates of Prophylaxis—Reply

In reply

The letter from Dr Moler identifies a common issue in interpreting cost-effectiveness analyses, namely, the assumptions used in the calculations. One goal in performing our cost-effectiveness analysis was to avoid assumptions that would overestimate the true cost of RSV prophylaxis with palivizumab. In the Impact trial, infants at 35 weeks' gestation or less and aged 6 months or younger were enrolled in the study with infants aged 24 months or younger with ongoing treatment for bronchopulmonary dysplasia. These enrollment criteria resulted in a mean age and weight of approximately 6 months and 4.9 kg, respectively. In our analysis we included only infants at 32 weeks' gestation or less and assumed prophylaxis for infants younger than 1 year. Excluding infants at 32 to 35 weeks' gestation (many of whom would be heavier at age 6 months than would infants at <32 weeks' gestation) and infants older than 1 year would lower the mean weight of our cohort and make 3.5 kg a more accurate assumption for our population. Dr Moler's point that weight assumption can greatly affect a drug cost analysis is a valid one. The importance of weight assumption can be emphasized using a sensitivity analysis (Figure 1). The range of $24 695 to $89 119 per hospitalization prevented dramatically underscores Dr Moler's point.