The purpose of this study is to assess the time for patients to relapse when switched from an oral antipsychotic to one of two doses of long-acting risperidone injection (shots). Risperidone has been used successfully to treat schizophrenia and schizoaffective disorder.

Results from studies of older long-acting injectable antipsychotics (not risperidone) show that patients tend to relapse (which means start having symptoms again) when they are given low doses. However, increasing the dose may cause more side effects. This study will measure the time to relapse during a 52-week period in patients with schizophrenia or schizoaffective disorder who are switched from an oral antipsychotic (one taken by mouth) to one of two doses of long-acting risperidone injections (shots). The patients will be assigned to a dose of either 25 or 50 milligrams per injection every 2 weeks. Patients continue to take their usual oral antipsychotic medications up to 3 weeks following the first injection. After this 3-week period, they will receive the injectable risperidone only. Patients will be asked questions at each visit to help determine the effectiveness of the drug as assessed by the Clinical Global Impression Scale and the Positive and Negative Syndrome Scale. The safety of the drug will be based on patient signs and symptoms assessed according to the Extrapyramidal Symptom Rating Scale and self-reported treatment-emergent adverse events. Long-acting risperidone injection, 25 or 50 milligrams per injection, every 2 weeks for 52 weeks. Patients will continue to take their current oral antipsychotics for up to 3 weeks following the first injection of risperidone.

Inclusion Criteria:

• Patients diagnosed with schizophrenia or schizoaffective disorder
• stable with respect to disease symptoms and other medical conditions
• stable on any oral antipsychotic drug (except clozapine) for 4 weeks before the study
• patients identify a relative or acquaintance who can complete a questionnaire with additional information about the patient
• if female, using birth control.

Exclusion Criteria:

• Patient is not eligible if currently hospitalized, or was treated for an acute disease-related crisis within the past 4 weeks
• at risk to self or others
• use of injectable antipsychotic drugs or electroconvulsive therapy within past 6 months, or currently using carbamazepineor an oral antipsychotic drug in a dose that is higher than 8 milligrams per day in risperidone equivalents, of long-acting risperidone in an earlier study, of clozapine, or use of investigational drugs within 30 days, or of electroconvulsive therapy within past 6 months
• presence of liver or kidney damage
• history of neuroleptic malignant syndrome
• if pregnant or breast-feeding
• not using birth control
• abusing drugs or alcohol.