Risperidone ISM as a New Option in the Clinical Management of Schizophrenia: A Narrative Review

Antipsychotics are the cornerstone of schizophrenia treatment. Lack of treatment adherence encouraged the development of injectable long-acting antipsychotics. However, second-generation or atypical antipsychotics require a loading dose at the start of treatment and eventually oral supplementation to achieve therapeutic plasma levels. This review discusses the evidence emerging from studies evaluating the pharmacokinetics, efficacy and safety of the intramuscular formulation of risperidone based on in situ microparticles (ISM). ISM® technology applied to risperidone allows therapeutic levels of the active moiety to be achieved within 2 h of intramuscular administration without the need for loading doses or oral supplementation, leading to a constant release over the whole dosing period. Risperidone ISM showed significant antipsychotic efficacy versus placebo in the Positive and Negative Syndrome Scale (PANSS) total score (p < 0.0001) and on the subscales of positive symptoms after 8 days, negative symptoms in 8 weeks, and general psychopathology during the 12 weeks of treatment. The improvement was also statistically significant (p < 0.0001) against placebo in the Clinical Global Impressions-Severity of Illness scale (CGI-S) score at the end of the treatment. Risperidone ISM was generally well tolerated and the most frequently reported adverse events were similar to those observed with other risperidone formulations. There is clinical evidence that these results are maintained in the long term. In conclusion, four-weekly risperidone ISM (75 mg and 100 mg) is an adequate antipsychotic for treating schizophrenia, both in the short term when an exacerbation has recently occurred and for long-term maintenance, since it provides rapid onset of action and sustained efficacy, as well as being safe and well tolerated.