Clinical Consequences of Inadvertent Intramuscular Administration of Subcutaneous Risperidone Formulation.

Long-acting injectable (LAI) antipsychotics have been predominately administered intramuscularly (IM). Recently, subcutaneous (SC) formulations have been developed. Information regarding what occurs when the drug is not administered properly is lacking. A 23-year-old woman with bipolar disorder, currently manic with psychosis, was responding well to a combination of lithium and risperidone. She accepted a LAI of SC risperidone, but the drug was administered IM by error. The improvement she had already displayed was partially lost, and oral risperidone had to be reinitiated. She complained of mild pain at the injection site, but no other adverse consequences were noted. When a SC formulation is administered IM, it results in mild muscle pain, and unpredictable release of risperidone, but no other notable clinical problems.