Decision analysis model evaluating the cost-effectiveness of risperidone, olanzapine and haloperidol in the treatment of schizophrenia

Purpose To evaluate the cost-effectiveness of three antipsychotic medications (olanzapine, risperidone and haloperidol) in the treatment of schizophrenia using the Positive and Negative Symptom Scale. Study design and methods A decision analysis model was created to evaluate the cost-effectiveness of two atypical antipsychotics (risperidone and olanzapine) and haloperidol. Outcome probabilities were determined from published clinical trials. The main dependent variable of interest was to compare the incremental cost-effectiveness ratios (ICER) of the atypical antipsychotic with haloperidol, and also to compare the ICER of olanzapine and risperidone. Sensitivity analyses were conducted for olanzapine and risperidone to determine the effects of altering drug cost, efficacy and re-hospitalization rate on total costs. Results Risperidone and olanzapine were dominant strategies compared with haloperidol (less costly and more effective). Risperidone was also dominant when compared with olanzapine. A one-way sensitivity analysis for efficacy indicated that the efficacy of risperidone would need to decrease by approximately 3% from the base-case in order for olanzapine and risperidone to have equal total costs. In a two-way sensitivity analysis varying both the cost of olanzapine and risperidone, the difference in drug costs between them would have to increase from $2.12 per day to $4.12 per day in order to have equal total costs. In terms of varying re-hospitalization rates, the re-hospitalization rate for risperidone would have to increase from 3% to 33% greater than the re-hospitalization rate for olanzapine in order to have equal total direct costs. Conclusion Based on this decision model, atypical antipsychotics were a dominant strategy over haloperidol primarily because of increased efficacy and lower re-hospitalizations. The ICER indicated that risperidone was dominant over olanzapine because of lower drug costs and increased number of responders, which leads to decreased total costs.