The delivery systems of two long-acting formulations of methylphenidate (MPH) were designed for different durations. Diffucaps bead-delivery system (DBDS)-MPH was designed to last 8 h and osmotically controlled-release oral delivery system (OROS)-MPH was designed to last 12 h. While the plasma pharmacokinetics and timing of efficacy have been studied, the corresponding central nervous system dopamine transporter (DAT) occupancies are unknown. In this study, 21 healthy volunteers underwent PET imaging with 11C Altropane before and after administration of oral doses of DBDS-MPH and OROS-MPH. Each subject received 40 mg DBDS-MPH and 36 mg OROS-MPH on different days. PET imaging occurred at 10 h after dosing. Each subject was injected with 5 mCi of 11C Altropane and serial images of the brain were acquired over 60 min with a Siemens HR+ PET camera. Binding potentials (BP, k3/k4) were calculated from time-activity curves using the simplified reference region method with cerebellum as reference. Transporter occupancy was calculated by standard methods. At 10 h, plasma d-MPH levels were lower (3.8±1.2 vs. 5.2±2.0) and brain DAT occupancy was lower (34.8±12.9 vs. 44.3±11.8) for DBDS-MPH than OROS-MPH. Across the range of values, for each unit of change in plasma d-MPH level there was a larger change in DAT occupancy with the DBDS-MPH formulation than with the OROS-MPH formulation. As predicted from previous pharmacokinetic and efficacy data, the average plasma level and DAT occupancy of 36 mg OROS-MPH was >40 mg DBDS-MPH at 10 h. Moreover, a relatively small difference in plasma levels (1.4 ng/ml at 10 h) was associated with a more impressive difference in DAT occupancy (≈10% at 10 h).

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