Risperidone versus haloperidol: II. Cost-effectiveness.

Australia and Canada are currently the only Western nations with government guidelines for analyzing the cost-effectiveness of drugs. We used guidelines issued by the Australian Pharmaceutical Benefits Advisory Committee to construct a model for comparing the cost-effectiveness of risperidone and haloperidol over a 2-year period in patients with chronic schizophrenia. Use of clozapine was also included in the analysis as an alternative treatment given to patients who proved unresponsive to therapy with haloperidol or risperidone. Results are expressed in Australian dollars. Cost-effectiveness was determined by using decision-analytic modeling to compare clinical outcomes and costs. The analytic model contained a decision tree for each of the compared agents that tracked the distribution of patients between treatment outcome pathways (i.e., scenarios). Distributions were based on probabilities derived from our meta-analysis results reported elsewhere and from other sources. Each scenario had an associated monetary cost that included all significant direct costs (i.e., hospital costs; outpatient costs; and the cost of drugs, the services of health care professionals, and government-subsidized hostel accommodation). The cost for a given outcome was the sum of costs for all scenarios leading to that outcome. Cost-effectiveness was expressed as the total cost per favorable outcome. The definition of a favorable outcome was one in which the patient was in a response phase at the end of the 2-year period. The probability of a patient experiencing a favorable outcome at the end of 2 years was 78.9% for risperidone versus 58.9% for haloperidol. The total cost of treatment for 2 years was $15,549.00 for risperidone versus $18,332.00 for haloperidol. The expected cost per favorable outcome was $19,709.00 for risperidone and $31,104.00 for haloperidol. Risperidone was more cost-effective than haloperidol and therefore was "dominant" in pharmacoeconomic terms because it produced a higher proportion of favorable outcomes at lower cost. Sensitivity analysis showed that the difference in clinical response rate was a key determinant of cost-effectiveness.