A Case of Clozapine Toxicity Caused by Infection in a Patient with Treatment-Resistant Schizophrenia

Clozapine is an effective antipsychotic for the treatment of treatment-resistant schizophrenia, but its use is associated with a risk of serious adverse events, especially when plasma levels of the drug exceed the therapeutic reference range. Infections have been reported to contribute to clozapine toxicity, although the underlying mechanisms remain incompletely understood.

We report the case of a woman in her seventies with treatment-resistant schizophrenia who developed clozapine intoxication, with plasma levels exceeding 3000 ng/mL, following an infectious episode. The patient had been receiving clozapine (300 mg/day) for one year without adverse effects. However, she developed fatigue and severe motor impairment and was found to have elevated levels of inflammatory markers and multiple infectious sources, including a pulmonary abscess, a pelvic abscess, and a decubitus ulcer. Upon admission, her plasma clozapine level was 3085 ng/mL. No changes in concomitant medications were identified, and the electrocardiography (ECG) findings were unremarkable. With antibiotic therapy and a gradual reduction in clozapine dose, her plasma levels reduced, and her symptoms were alleviated. She was discharged after 18 weeks of hospitalization.

This case highlights the potential for infection-induced clozapine intoxication even at relatively moderate doses of the drug. Regular monitoring of clozapine plasma levels is critical for the early identification and prevention of abnormal elevation of clozapine levels, especially.