A clozapine conundrum: clozapine toxicity in an acute medical illness

The following report presents a case in which significant clozapine toxicity was demonstrated in a patient on established therapy, in the absence of identifiable risk factors. Through this case report, the authors aim to highlight the potential for clozapine toxicity to occur unexpectedly in times of acute medical illness, and the need to remain vigilant in such situations.

Case report and review of the relevant literature.

We describe a case of a 62 year old man whom developed life-threatening clozapine toxicity in the context of a severe lower respiratory infection. Following investigation to exclude the usual causes of toxicity, it was surmised that impaired CYP1A2 function, secondary to the acute inflammatory process, had led to a toxic level of the drug.

Given the possibility that serum clozapine levels may significantly rise in acute illness, the team recommends measurement of clozapine levels in these situations, in combination with the usual full blood count investigation. Such a practice should be considered in the local monitoring protocol, to avoid incidence of potentially toxic outcomes.