Expansion of guidance for the day 8 initiation dose of paliperidone palmitate to avoid a missed dose

BACKGROUND: Paliperidone palmitate (PP) is a long-acting injectable formulation of an atypical antipsychotic, paliperidone. Its dose can be expressed in milligram or milligram equivalents (mg eq) of active paliperidone (39, 78, 117, 156, and 234 mg of PP correspond to 25, 50, 75, 100, and 150 mg eq of paliperidone). The recommended initiation dosing regimen for PP is 150 [day 1]/100[day 8] mg eq. Labeling guidance allowed a ± 2 day window for the day 8 injection that provides more flexibility with patient scheduling and avoids missing the day 8 initiation dose. Recently, expansion of the day 8 dosing window from ±2 to ±4 days has been approved in the United States based on results obtained from the model-based simulations and review of safety data presented here. METHODS: The predicted exposure for the recommended initiation regimen of PP was compared with day 1/day 4, and day 1/day 12 dosing scenarios; each scenario was compared with the highest clinically evaluated initiation regimen (150[day 1]/150[day 8] mg eq) and to the recommended 6 mg/day oral dose of extended-release paliperidone. RESULTS: Simulated exposures with PP 150 mg eq on day 1 and 100 mg eq on days 4, 8, or 12 overlap considerably, with ±3 ng/mL variation in median maximum plasma concentrations. Based upon pharmacokinetic bridging/bracketing, the peak concentration with PP 150/100 mg eq [days 1/4] was lower than that with the highest initiation regimen. Exposures for PP 150 mg eq on day 1 and 100 mg eq on days 4, 8, or 12 were maintained close to those of 6 mg of paliperidone extended-release. CONCLUSION: These simulations indicate that using the expanded dosing window of ±4 days has little effect on paliperidone exposure. A review of the overall pattern of treatment-emergent adverse events did not identify any new safety risks associated with the expanded dosing window.