Economic evaluation of insulin lispro versus neutral (regular) insulin therapy using a willingness-to-pay approach

This willingness-to-pay (WTP) analysis is the first study of its kind undertaken in Australia to support an application for listing of a new drug on the Australian national formulary. The technique offers the advantage of being able to summarise diverse outcomes of therapy in a single unit of measure. Willingness to pay is used to value benefits in cost-benefit analysis (CBA), and CBA represents an absolute decision rule. An open-ended question with a bid-up approach was used to minimise bias and elicit the maximum amount patients would be willing to pay for insulin lispro. The WTP study incorporated scenarios describing the outcomes from insulin lispro and neutral (regular) insulin, the results from a formal metaanalysis and a description of the injection characteristics of the therapies. A sample of 83 patients with type I or II diabetes mellitus were surveyed using an open questionnaire to determine their maximum willingness to pay for the therapy they preferred. Overall, 92% of patients preferred insulin lispro (referred to as insulin A) and 8% preferred neutral insulin (referred to as insulin B). The incremental benefit per patient was calculated as 452.16 Australian dollars ($A) per year. Insulin lispro was listed on the Australian national formulary at a 36% premium over neutral insulin, so the additional cost per patient would be $A70.32 per year. Therefore, costs were exceeded by the benefits and insulin lispro was deemed to offer a net benefit. A multivariate analysis indicated that those patients who were middle-aged had the strongest preference for insulin lispro.