Effect of Dosage Forms on the Steady-State Dose-Corrected Plasma Concentrations of Quetiapine and N-Desalkylquetiapine.

BACKGROUND: This study aimed to determine the effects of dosage forms on the steady-state dose-corrected (C/D) concentrations of quetiapine and N-desalkylquetiapine in patients. METHODS: This was a retrospective cohort study that included 831 therapeutic drug monitoring samples derived from 512 patients. Multiple linear regression analysis was used to identify independent factors that affected the C/D values for quetiapine and N-desalkylquetiapine. Moreover, we compared the C/D values of quetiapine and N-desalkylquetiapine between the two groups and conducted subgroup analyses based on daily dose, sex, and age. RESULTS: The C/D ratio of quetiapine in the extended-release (XR) group was 1.7-fold higher compared with that in the immediate-release (IR) group (P < 0.001); however, no statistically significant difference was observed in the C/D ratio of N-desalkylquetiapine between the two subgroups (P > 0.05). In the subgroups stratified by daily dose, sex, and age group, the C/D ratios of quetiapine in the XR group were 1.31-2.65-fold higher compared with that in the IR group (all P < 0.001). No significant differences were observed in the C/D ratio of N-desalkylquetiapine among the subgroups (P > 0.05). CONCLUSION: Dosage form significantly affects the steady-state C/D ratio of quetiapine; however, it does not significantly affect the C/D ratio of N-desalkylquetiapine.