Clozapine Efficacy and Adverse Drug Reactions Among a Nationwide Study of 1021 Australians Prescribed Clozapine: The ClozaGene Study

Abstract

Background and hypothesis: The ClozaGene Study is a nationwide cohort of adults who have been treated with clozapine. While clozapine is indicated in the management of treatment-resistant schizophrenia, it is associated with a considerable adverse drug reaction (ADR) burden, and not all patients achieve adequate symptomatic response. The current study focuses on self-reported experiences of clozapine use and response, clozapine-associated ADRs, and mental health comorbidity.

Study design: A total of 1021 participants (41.0% female; aged 46.2 ± 10.6 years [range 18-66]) were recruited via a mail-out based on prescriptions for clozapine. Participants completed a self-report questionnaire.

Study results: Most participants (90.1%, n = 912) were living with schizophrenia while 41.5% reported a lifetime diagnosis of depression, 15.6% bipolar disorder, and 8.1% schizoaffective disorder. Clozapine was currently prescribed to 944 (92.5%) participants and 37.8% of these participants self-reported currently taking additional antipsychotic medication. Nearly 3 quarters of participants living with schizophrenia reported that clozapine helped control their schizophrenia symptoms moderately to very well. The most commonly reported ADRs were sialorrhea (80.3%), weight gain (71.0%), constipation (56.9%), and sedation (52.8%). The prevalence of clozapine cessation due to clozapine-induced myocarditis and neutropenia was 1% and 0.4%, respectively.

Conclusions: Our findings highlight the high rate of psychotic and metabolic symptoms and ADRs among adults prescribed clozapine in the general Australian population. Future genomic analyses will focus on identifying genetic variants influencing clozapine treatment response and side effects.

Keywords: effectiveness; metabolic disorders; treatment-resistant schizophrenia.

Fig. 1.

Frequency of clozapine adverse drug reactions^† ever experienced by gender. ^†The adverse drug reactions for sialorrhea and heart problems were listed as “excessive saliva/drooling” and “heart problems (eg, chest pain, fast heartbeat, high blood pressure)”, respectively.