Risperidone-ISM is a new long acting intramuscular formulation of risperidone, for monthly administration without oral supplementation.

To characterize the pharmacokinetic of risperidone over multiple intramuscular injections in patients with schizophrenia.

A multicenter, open label, two-arm, parallel design clinical trial was performed. Each patient received 4 intramuscular injections of 75 mg of risperidone-ISM in either, gluteal or deltoid muscle at 28-day intervals.

A total of 70 patients were randomized, 67 received at least one dose of study medication. Preliminary data show that mean Cmax of the active moiety was achieved 24-48 hours (Tmax) after each administration and ranged over four consecutive doses from 39.6-53.2 ng/mL and 54.1-61 ng/mL, when given in gluteal or deltoid, respectively. All subjects achieved therapeutic levels (> 7.5 ng/mL for the active moiety) between 2-8 hours after drug administration. The mean concentrations were maintained above therapeutic levels throughout the 4-week dosing period. No significance changes across the study were observed, either on Positive and Negative Syndrome Scale or Extrapyramidal Symptoms Scale. Overall, 63 subjects (94%) experienced at least 1 Treatment Emergent Adverse Event (TEAE) during the study. One serious TEAE (dystonia) was related to study treatment. One death not related to study medication was informed. The most frequently reported TEAEs were hyperprolactinaemia (57.7%) and injection site pain (32.8%).

Risperidone-ISM achieved therapeutic levels from the first hours after drug administration and provided a sustained release throughout the 4-weeks dosing period over multiple intramuscular injections independently of the injection site. Risperidone-ISM was found to be safe and well tolerated.

The authors have not supplied their declaration of competing interest.