Clinical Factors Affecting Constipation in Patients with Schizophrenia Taking Clozapine

Objectives: To investigate clinical factors affecting constipation in patients with schizophrenia taking clozapine.Methods: The participants were patients with schizophrenia taking clozapine and tested for the Therapeutic Drug Monitoring from September 1, 2020 to July 1, 2022 at a university hospital. To evaluate the effect of clozapine on constipation, clozapine dosage, clozapine concentration, and norclozapine concentration were investigated. To evaluate effects of drugs other than clozapine on constipation, dosage and type of other drug were investigated. Anticholinergic Drug Scale was used to evaluate anticholinergic action.Results: A total of 56 patients were enrolled in the study. Clozapine daily dose, clozapine concentration, and norclozapine concentration were higher in the constipated patient group. Through logistic regression analysis, it was discovered that the risk of constipation increased as the norclozapine concentration increased, and the results remained similarly even after adjustments of related variables was performed.Conclusion: It was discoverd that among patients taking clozapine, the higher the norclozapine concentration, the higher the probability of constipation. Among patients taking clozapine, patients with high norclozapine concentration may need additional evaluation and management of constipation.