Recommendations for the monitoring of serum concentrations of antipsychotic drugs in the treatment of schizophrenia.

A 40-year-old man with schizophrenia is being treated with the longacting injectable form of risperidone. He comes to a community clinic for his second 50-mg dose since beginning treatment. His psychiatrist instructs him to stop concomitant use of oral risperidone 1 week after the second injection, as is recommended by the drug manufacturer. Three days following discontinuation of oral risperidone, the patient becomes fearful that his son, who lives with his ex-wife, has been kidnapped. He reaches this conclusion based on FBI and CIA radio transmissions that he believes he can hear being emitted from parked cars. He attempts to contact his family with this information and ultimately calls the police to his ex-wife’s home. When his family gets word of his decompensation, they bring him to the closest emergency room and he is admitted to an inpatient psychiatric facility. On admission, his combined serum level of risperidone and 9-OH-risperidone is found to be 10.4 ng/mL, approximately half the lower limit of the therapeutic range recommended by AGNP guidelines. Could evaluation of his serum level of risperidone prior to discontinuation of the oral medication have prevented this relapse and rehospitalization?