title: Factors predicting use of laxatives in outpatients stabilized on clozapine.
abstract: Constipation is a common and sometimes fatal side effect of clozapine treatment. In this study, we aimed to identify factors associated with clozapine-induced constipation. Data on 202 outpatients stabilized on clozapine treatment were collected. Of these, 71 patients (35%) had a current prescription for laxatives (a proxy for the presence of constipation). Mean clozapine dose was 400.4 mg/day in those prescribed laxatives and 390.1 mg/day in those not prescribed laxatives (p = 0.67), while mean clozapine plasma concentration was 0.53 mg/l and 0.49 mg/l, respectively (p = 0.29). Patients using laxatives had on average 29% higher norclozapine concentrations (mean = 0.34 mg/l) than those who did not use laxatives (mean = 0.27 mg/l; p = 0.046). Laxative use was more common in female patients (49.1%) than male patients (29.1%; p < 0.01). Prescribers should be vigilant for constipation at any dose or plasma concentration of clozapine and should be mindful that male patients may be undertreated. Norclozapine concentrations may predict clozapine-induced constipation.
authors.affiliation: Bethlem Royal Hospital, Pharmacy Department, UK.
authors.forename: Loren
authors.initials: L
authors.lastname: Bailey
authors.affiliation: Maudsley Hospital, Pharmacy Department, UK.
authors.forename: Seema
authors.initials: S
authors.lastname: Varma
authors.affiliation: Breakspear Pharmacy, UK.
authors.forename: Nina
authors.initials: N
authors.lastname: Ahmad
authors.affiliation: Bethlem Royal Hospital, Pharmacy Department, UK.
authors.forename: Siobhan
authors.initials: S
authors.lastname: Gee
authors.affiliation: Institute of Pharmaceutical Science, King's College, London, 5th Floor, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, UK.
authors.forename: David M
authors.initials: DM
authors.lastname: Taylor
keywords: N-desmethylclozapine; clozapine; constipation; laxatives