Effect of carbamazepine on the pharmacokinetics of paliperidone extended-release tablets at steady-state

Given the potential concomitant use of carbamazepine and paliperidone extended-release (ER) in the treatment of schizophrenia or schizoaffective disorder, this open-label, two-treatment sequential study investigated the effect of repeated administration of carbamazepine on the steady-state pharmacokinetics of paliperidone. Sixty-four patients with a diagnosis of schizophrenia or bipolar-I disorder received the following treatments in a fixed sequential order, without washout between treatments: (i) paliperidone ER 6 mg tablet once daily for 7 days, and (ii) paliperidone ER 6 mg once daily concomitantly with carbamazepine 200 mg twice daily for the subsequent 21 days. Upon coadministration with carbamazepine, paliperidone steady-state total exposure (AUC24 h ) and peak plasma concentrations (Cmax ) decreased by approximately 37% [LSM ratio-AUC24 h : 63.4 (90% CI: 57.19; 70.29); Cmax : 62.47 (90% CI: 55.77; 69.98)]. This decrease is accounted for to a substantial degree by a 35% increase in renal clearance of paliperidone, likely as a result of induction of renal P-glycoprotein by carbamazepine. A 14% decrease in the amount of drug excreted unchanged in the urine suggests that carbamazepine coadministration has a limited effect on the intestinal absorption or cytochrome metabolism of paliperidone.