Pharmacokinetics and D2 receptor occupancy of long-acting injectable risperidone (Risperdal Consta™) in patients with schizophrenia

Thirteen patients with schizophrenia received injections of 25, 50, or 75 mg of long-acting risperidone every 2 wk. Brain D2 receptor occupancy was assessed with [11C]raclopride 2 wk after the last (fifth) injection (day 71) in seven subjects and 2 wk after the third injection (day 44) in one subject. Stable plasma concentrations were reached after the third injection and steady-state concentrations of the active moiety (risperidone + 9-hydroxyrisperidone) after the fourth injection. Steady-state plasma concentrations were maintained for 4-5 wk after the last injection and then declined rapidly. After injections of 25, 50 and 75 mg on day 44 or day 71, D2 receptor occupancy ranged from 25-48%, 59-83% and 62-72% respectively, while plasma active-moiety levels ranged from 4.4-8.8, 15.0-31.1 and 22.5-26.3 ng/ml respectively. The results indicate that brain D2 receptor occupancy at steady state after injections of long-acting risperidone was in the range found in patients effectively treated with 2-6 mg of oral risperidone.