Respiratory Infections Rather Than Antibiotics May Increase Clozapine Levels: A Critical Review of the Literature

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Sir: Approximately 70% of clozapine metabolism is explained by the cytochrome P450 1A2 (CYP1A2).¹ The CYP1A2 can be inhibited by respiratory infections. Decreased theophylline (a CYP1A2 substrate) clearance during upper respiratory infections has been described in asthmatic children^2,3 and in adults with chronic bronchitis.⁴