Effects of Dose, Age, Sex, Body Weight, and Smoking on Plasma Concentrations of Olanzapine and N-desmethyl Olanzapine in Inpatients With Schizophrenia

Abstract Purpose This study aimed to investigate the combined effects of dose, age, sex, body weight, and smoking on plasma concentrations of olanzapine (OLA) and N-desmethyl olanzapine (DMO) in Chinese inpatients with schizophrenia. Methods A retrospective study including 185 inpatients was conducted. The steady-state plasma concentrations of OLA (C OLA ) and DMO (C DMO ) were measured using high-performance liquid chromatography-tandem mass spectrometry. The combined effects of dose, age, sex, body weight, and smoking on C OLA and C DMO were evaluated. Findings Multiple linear regression analyses revealed that dose, age, body weight, and smoking had significant effects on C OLA and C DMO in inpatients with schizophrenia treated with OLA. The dose was the most important determinant of C OLA and C DMO and was positively correlated with both. Furthermore, smokers exhibited a significantly lower C OLA and C OLA + DMO , whereas higher body weight led to the reduction of C OLA , C DMO , and C OLA + DMO . Advanced age was associated with lower C DMO . Implications These results suggest that dose, age, body weight, and smoking have a significant influence on the plasma concentration of OLA and its metabolite DMO. Clinicians should consider the combined effects when prescribing OLA to patients with schizophrenia.