Partial or non-response to clozapine is a challenging clinical situation. For these patients, who are considered refractory or ultra-resistant, we have limited options. Available evidence for augmenting clozapine is discouraging, but even negative trial results are valuable as a guide for what not to do. Exposing patients to ineffective treatments increases both costs and risk of adverse effects.
Pimozide, a potent D2 receptor antagonist, was found to be effective in a 1997 open-label clinical trial in partial clozapine responders. In a 2011 double-blind, placebo-controlled, 12-week trial in patients with partial or non-response to clozapine, pimozide at a mean dose of 6.5 mg daily was ineffective (1). A different U.S. group just published another randomized, double-blind, placebo-controlled trial of pimozide at 4 mg daily in patients with partial clozapine response (2). Using the BPRS, the Schedule for the Assessment of Negative Symptoms, and evaluations of verbal memory, working memory and executive function, the investigators found no significant differences between the groups at 12 weeks, although both showed improvement in the BPRS over time.
With two negative trials, it seems that pimozide as a clozapine augmentation agent can be put to rest. In fact, the entire strategy of adding first-generation D2 antagonists to clozapine for partial or non-repsonse is dubious.
1. Friedman JI, Lindenmayer JP, Alcantara F, et al. Pimozide augmentation of clozapine in patients with schizophrenia and schizoaffective disorder unresponsive to clozapine monotherapy. Neuropsychopharmacology. 2011;36:1289-1295. Full text
2. Gunduz-Bruce H, Oliver S, Gueorguieva R, et al. Efficacy of pimozide augmentation for clozapine partial responders with schizophrenia. Schizophr Res. 2013;143:344-347. Abstract