Risperidone is not only a prodrug: psychosis induced by medication switch from risperidone to paliperidone – a case report

Once administered, risperidone is converted into its pharmacologically active form, paliperidone. Thus, their pharmacological effects are expected to be equivalent. We encountered a psychosis induced by the switch from risperidone to paliperidone.This is the case of a schizoaffective patient stabilised on risperidone long-acting injection (LAI) who consented to switch to paliperidone LAI. On day 0, he received his first dose of paliperidone. On day 86, he presented to the emergency department with an acute psychotic episode. On day 92, he committed a violent act. The patient was restarted on risperidone LAI and stabilised.Risperidone is extensively metabolised to paliperidone via CYP450 2D6. Interindividual and ethnic genetic polymorphism cause variability in CYP450 2D6 phenotypes. In this possible case of low-functioning alleles, the patient had a higher risperidone to paliperidone ratio at steady state. Although risperidone is paliperidone's prodrug, this case highlights the interindividual pharmacotherapeutic response to these two antipsychotics.