Clozapine plasma level monitoring: current status

Plasma level monitoring of clozapine and metabolites may prove beneficial in treating patients who show unusual drug metabolic activity. A threshold plasma level for patients who will respond to this medication is suggested. The interaction of gender, age, smoking, other medication and side effects with plasma clozapine and metabolites are discussed. Plasma level monitoring of clozapine and/or metabolites is recommended in patients who do not respond at usual therapeutic dose, who show untoward side effects at low dose or who are treated with other medications. Finally monitoring of patients who require more than 600 mg/day should be implemented because there is evidence that the incidence of seizures increases significantly above this dosage level. There is some evidence that high plasma clozapine levels are associated with seizures.