A Pharmacokinetic and Safety Study of Risperidone Long Acting Injectable in Schizophrenic Patients

This is an open-label, multicenter, randomized, 3-arm trial to compare the pharmacokinetic profile and the safety profile between 3 dose groups. There are 2 periods in this study: a 10-week treatment period and an 8-week follow-up period. Patients will receive 6 injections of long acting injectable risperidone at one of the dose levels (25, 37.5 and 50 mg) every 2 weeks according to their randomly assigned treatment. Blood samples will be collected throughout the 10-week treatment and 8-week follow-up period to determine the changes in study drug concentration in the plasma. Safety will be assessed by monitoring of adverse events, subjective symptoms/objective findings, laboratory tests, physical examinations, electrocardiograms, injection site reactions, and the Drug-Induced Extrapyramidal Symptoms Scale (DIEPSS). Efficacy of the study drug will be assessed based on the Positive and Negative Syndrome Scale (PANSS) and the Clinical Global Impression - Severity (CGI-S) and Clinical Global Impression - Change (CGI-C) scales. The patients will receive injections of long acting injectable risperidone (either 25, 37.5, or 50 mg) in their muscle every 2 weeks for 10 weeks for a total of 6 injections.