Increased Efficacy With Addition of Clozapine to Aripiprazole: Alternative Explanations

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Sir: I read with interest the letter entitled "Possible Increased Efficacy of Low-Dose Clozapine When Combined With Aripiprazole" by Lim et al.¹ The authors describe 3 cases of individuals suffering from psychotic disorders who apparently responded to combined therapy with clozapine and aripiprazole. In each case, the patient had not responded to therapeutic doses of aripiprazole (15-45 mg per day). As a result of persistent psychotic symptoms, each patient was hospitalized, the patient’s aripiprazole dose was adjusted to 15 to 30 mg per day, and modest doses of clozapine were added. Despite total clozapine doses that are considered low, 150 to 200 mg/day (and total serum clozapine levels that ranged from 181-610 ng/mL), each patient demonstrated substantial symptomatic improvement (Brief Psychiatric Rating Scale scores decreased 24%-53%).’ ‹’ ‹