Clinical review of a long-acting, injectable formulation of risperidone

A long-acting, injectable risperidone formulation is the first depot atypical antipsychotic drug to become available in the United States.

The intent of this article is to review the efficacy and safety data available for long-acting, injectable risperidone.

Information was identified via MEDLINE (years, 1990-May 2004) using the terms risperidone, long-acting injectable, depot, and delayed-action preparations. The manufacturer also provided information about risperidone in the form of abstracts and summaries of professional meetings.

Several 12-week studies and one 12-month study suggest that long-acting risperidone is an effective and well-tolerated treatment option for the maintenance therapy of schizophrenia. Thus far, no unexpected adverse events have been reported with the long-acting formulation. Extrapyramidal symptoms with long-acting risperidone were uncommon, dose-related, and similar to those observed with oral risperidone in short-term trials. A small, dose related weight gain occurred with long acting risperidone, again similar to that seen with oral risperidone. Pain at the injection site was uncommon and decreased with continued administration. The long-acting, injectable formulation comes in an aqueous suspension of microspheres. There is no initial drug release after injection; the main release of risperidone begins at week 2 to 3 postinjection, increases during weeks 3 and 4, is maintained during weeks 4 through 6, and declines between weeks 6 and 7. With repeated injections every 2 weeks, steady-state levels are usually reached by weeks 6 to 8. For most patients, the initial dosage should be 25 mg every 2 weeks, and oral administration should continue for the first 3 weeks after initial injection. Doses can be increased every 8 weeks to a maximum of 50 mg every 2 weeks.

Long-acting risperidone offers clinicians a combination of the benefits of a depot antipsychotic drug with the therapeutic advantages of an atypical antipsychotic drug.