A Study of Dopamine Type 2 (D2) Receptor Occupancy Following a Single Oral Dose of OROS Paliperidone

This is a single-center, single-dose, open-label, Phase-1 Positron Emission Tomography (PET) study in 4 healthy volunteers, 2 men and 2 women. After screening, healthy eligible volunteers will be hospitalized in the study unit from study Day 2 to Day 4. On Day 1 (the day before hospitalization), volunteers will enter the study unit from 5:00 p.m. to 8:00 p.m. for baseline prolactin blood sampling and sedation assessment. Each volunteer will have a control magnetic resonance imaging (at screening) and 3 PET measurements using the radioligand \[11\]C raclopride to measure central D2 receptor occupancy in the putamen. Blood samples to measure plasma concentrations of paliperidone will be collect immediately before and at scheduled time points after dose administration on Day 2, and immediately before, halfway through, and immediately after the PET-2 and PET-3 measurements. Serum prolactin levels will be measured immediately before and at several scheduled time points after dose administration, and immediately before and after each PET measurement. At scheduled time points, supine and standing blood pressures, pulse, sensorium changes, temperature, and degree of sedation will be recorded, volunteers will be questioned about adverse events, and they will be evaluated for extrapyramidal symptoms (EPS). Adverse events will be recorded and followed throughout the study. The rationale for the study design is based on previous PET studies with risperidone, which indicated that PET measurement of D2 receptor occupancy after a single dose of medication is useful in predicting an effective clinical dose range. Single oral dose (6 mg) of OROS paliperidone