Pharmacokinetic profiles of extended release quetiapine fumarate compared with quetiapine immediate release.

This 10-day, single-center, open-label, randomized, crossover study compared pharmacokinetic profiles and tolerability of extended release quetiapine fumarate (quetiapine XR) with quetiapine immediate release (quetiapine IR) in patients with schizophrenia, schizoaffective disorder or bipolar disorder. After a 2-day lead-in period during which patients received quetiapine XR 300 mg once daily, patients were randomized to quetiapine IR 150 mg twice daily followed by quetiapine XR 300 mg once daily, or quetiapine XR 300 mg once daily followed by quetiapine IR 150 mg twice daily. Pharmacokinetic parameters were evaluated at the end of each 4-day treatment period at steady state. Vital signs, laboratory values, and adverse events (AEs) were recorded throughout the study. The least squares means (90% confidence interval) of the ratio of the area under the plasma concentration-time curve over a 24 h dosing interval (AUC ([0-24 h])) for quetiapine XR/IR was 1.04 (0.92-1.19) and within the pre-defined range set for equivalence (0.80-1.25). Maximum plasma concentration at steady state (C(max)) was approximately 13% lower for quetiapine XR than for quetiapine IR (495.3 versus 568.1 ng/mL), time to reach C(max) (t(max)) was 5 h versus 2 h and mean concentration at the end of 24 h dosing interval (C(min)) was 95.3 versus 96.5 ng/mL, respectively. No patients withdrew from the study owing to AEs and there were no serious AEs or deaths related to study medication. No unexpected AEs, changes in vital signs or laboratory values were observed. These findings suggest that modifying the formulation does not change the overall absorption or elimination of quetiapine, and support emerging clinical evidence for the use of quetiapine XR as a once daily treatment in patients initiating therapy or those established on quetiapine IR.