The Effect of Race-Ethnicity on the Comparative Effectiveness of Clozapine Among Medicaid Beneficiaries

Objective: Effectiveness trials have confirmed the superiority of clozapine in schizophrenia treatment, but little is known about whether the drug's superiority holds across racial-ethnic groups. This study examined the effectiveness by race-ethnicity of clozapine relative to other antipsychotics among adult patients in maintenance antipsychotic treatment. Methods: Black, Latino, and white Florida Medicaid beneficiaries with schizophrenia receiving maintenance treatment with clozapine or other antipsychotics between July 1, 2000, and June 30, 2005, were identified. Cox proportional hazard regression models were used to estimate associations between clozapine and race-ethnicity and their interaction; time to discontinuation for any cause was the primary measure of effectiveness. Results: The 20,122 members of the study cohort accounted for 20,122 antipsychotic treatment episodes; 3.7% were treated with clozapine and 96.3% with other antipsychotics. Blacks accounted for 23% of episodes and Latinos for 36%. Unadjusted analyses suggested that Latinos continued on clozapine longer than whites and that Latinos and blacks discontinued other antipsychotics sooner than whites. Adjusted analyses of 749 propensity score-matched sets of clozapine users and other antipsychotic users indicated that risk of discontinuation was lower for clozapine users (risk ratio [RR]=.45, 95% confidence interval [CI] =.39-.52), an effect that was not moderated by race-ethnicity. Times to discontinuation were longer for clozapine users. Overall risk of antipsychotic discontinuation was higher for blacks (RR=1.56, CI=1.27-1.91) and Latinos (RR=1.23, CI=1.02-1.48). Conclusions: The study confirmed clozapine's superior effectiveness and did not find evidence that race-ethnicity modified this effect. The findings highlight the need for efforts to increase clozapine use, particularly among minority groups.