Paliperidone poisoning and measurable plasma concentrations 2.5 years after last administered dose: A case report

We report a poisoning with paliperidone palmitate, a once-monthly, long-acting injectable antipsychotic. The patient suffered from deep sedation and dystonia. She had been treated with extended release intramuscular paliperidone for several years and had received her last injection 8 days prior to admission. The plasma paliperidone was nearly five times higher than the upper reference range. Paliperidone is a substrate of p-glycoprotein and we therefore aimed to increase its elimination by inducing p-glycoprotein through treatment with St John's wort. This seemed to have a limited effect on paliperidone clearance. Plasma concentration levels decreased with time as did the dystonia. All antipsychotic treatment was discontinued after this unfortunate event, and the patient did specifically not receive any prescriptions of paliperidone or risperidone. However, the plasma paliperidone concentration was in the low end of the normal therapeutic range 2.5 years after the last dose of paliperidone was administered, and the patient still had some extrapyramidal symptoms.