<jats:p>Draw TDM levels 12 hours after the last dose. Repeat any level that raises clinical concern before making important treatment decisions. Use TDM to verify prior failures involved therapeutic levels. Don't mistake non-adherence for true treatment resistance. Do not rely on a single unrepeated clozapine level. Variation of 20 to 30% between assays is not unusual, even under normal circumstances.</jats:p>