Risperidone long-acting injection: in bipolar I disorder

A long-acting intramuscular formulation of the atypical antipsychotic agent risperidone is now indicated for the maintenance treatment of patients with bipolar I disorder. The formulation utilizes a novel drug delivery system of biodegradable microspheres and is bioequivalent to the oral formulation of the drug. Moreover, fluctuations in plasma drug concentrations at steady state were 1.7-fold lower with long-acting than with oral risperidone. Maintenance treatment with risperidone long-acting injection, as monotherapy in adults with stabilized bipolar I disorder or as an adjunct to standard therapy in adults with stabilized, frequently relapsing bipolar I disorder, was effective in delaying relapse to symptoms in two well designed trials with maintenance phases of 1 or 2 years' duration. The time to relapse to any mood episode (primary endpoint) was significantly longer with risperidone long-acting injection than with placebo in both studies. Risperidone long-acting injection also significantly reduced the risk of relapse relative to placebo in these trials. Maintenance treatment with risperidone long-acting injection was generally well tolerated in patients with bipolar disorder, both as monotherapy and adjunctive therapy, with most adverse reactions being of mild to moderate severity.