Evaluating the Real-World Pharmacokinetics of Risperidone ISM® in Routine Clinical Practice

<b>Background/Objectives</b>: Risperidone ISM^® is a long-acting injectable (LAI) formulation approved for monthly administration in schizophrenia treatment. It employs innovative in situ microimplant technology for biphasic drug release, achieving immediate and sustained therapeutic plasma concentrations without the need for oral supplementation or loading doses. This study evaluates the pharmacokinetic profile of Risperidone ISM^® in a real-world clinical setting, focusing on plasma concentrations of the active moiety (Risperidone + 9-OH-Risperidone). <b>Methods</b>: An observational study was conducted to measure plasma concentrations of patients receiving Risperidone ISM^® (75 mg or 100 mg). Samples were collected at pre-dose, 2 h, 24 h, 14 days, 21 days, and 25 days post-injection. Pharmacokinetic parameters, including Cmax, Cmin, Tmax, and AUC, were calculated and stratified by dose (75 mg and 100 mg) and injection site (gluteal vs. deltoid). <b>Results</b>: A total of 44 patients were included. Therapeutic plasma levels were reached within hours post-injection and sustained throughout the 28-day interval. Cmin values averaged 34.4 ng/mL and 36.1 ng/mL for the 75 mg and 100 mg doses, respectively. The median Tmax occurred at 24 h with a mean Cmax of 55.7 ng/mL and 59 ng/mL for 75 mg and 100 mg, respectively. Higher systemic exposure was observed for deltoid administration. Significant interindividual variability was noted, with 45.4% of patients exhibiting trough levels outside the therapeutic range. <b>Conclusions</b>: Risperidone ISM^® achieves rapid and sustained therapeutic plasma levels, offering significant benefits in schizophrenia treatment. However, the high interindividual variability observed must be thoroughly studied, and the contributing factors identified to ensure the therapy is as effective and safe as possible.