Objective: To determine the cost utility of treating schizophrenic patients with olanzapine compared with other antipsychotics in a naturalistic outpatient setting. Methods: The pan-European SOHO study is a 3-year, prospective, outpatient, observational study of outcomes associated with antipsychotic treatment, focusing on olanzapine, in ten European countries. For the cost-utility analysis, healthcare resource use (inpatient care, day care, outpatient psychiatric consultations and antipsychotic and concomitant medication use) and EQ-5D data were collected at baseline and at 3, 6 and 12 months. The perspective was that of the health service payer. UK healthcare unit costs (year 2004 values) were applied to the resource use data for the ten countries. UK population tariffs were applied to the EQ-5D data to determine utility values. An Epoch analysis was used to analyze the longitudinal data. Multivariate regression analyses that adjusted for baseline covariates were used to estimate the incremental cost and utility gains for patients treated with olanzapine compared with each of the other antipsychotics (risperidone, quetiapine, amisulpride, clozapine and oral or depot typical antipsychotics). Results: A total of 10_972 patients were enrolled at baseline, of which 9107 completed the 12-month study period. Treatment with olanzapine was more effective in terms of QALYs gained than all of the other antipsychotic treatments. Treatment with olanzapine dominated quetiapine and amisulpride. The incremental cost for olanzapine compared with risperidone was Lstg 226 per patient over 12 months and the incremental cost per QALY gained was Lstg 5156, with bootstrap analyses showing 100% of the replications falling below a Lstg 30_000 per QALY gained threshold. Compared with treatment with clozapine, olanzapine was found to be marginally more effective, at an additional cost of Lstg 13 per patient over 12 months and to have an incremental cost per QALY gained of Lstg 775. Bootstrap analyses showed that 81% of replications fell below a Lstg 30_000 per QALY gained threshold. Comparing olanzapine with oral and depot typical antipsychotics, the incremental cost was Lstg 849 and Lstg 1106 per patient over 12 months and the incremental cost per QALY gained was Lstg 15_696 and Lstg 23_331, respectively. Bootstrap analyses showed that 98% of the replications fell below a Lstg 30_000 per QALY gained threshold for the comparison with oral typical antipsychotics, and 79% of replications for the comparison with depot preparations. Conclusions: Among SOHO patients, if a funding threshold of Lstg 30_000 per QALY gained is assumed, this analysis suggests that olanzapine has a high probability of being the most cost-effective treatment compared with other antipsychotic treatments. However, comparison of olanzapine with clozapine and typical depot antipsychotics should be viewed with caution because clozapine is a second-line treatment and depot treatment is used for patients who do not adhere to their oral medication.
