Are Same Day Clozapine Levels Necessary?

Clozapine is the only FDA-approved drug for treatment resistance schizophrenia (TRS) and is highly effective. However, clozapine is also the third most toxic drug in the US after oxycodone and fentanyl. In addition, clozapine has a crucial therapeutic range because if the blood level is too low, the patient is at risk for decompensation. If the clozapine blood level is too high, the patient is at risk for clozapine toxicity. These factors mean that same-day clozapine blood levels are critical to patient care to respond in real-time to tolerability and efficacy concerns. The following scenarios illustrate the impact of same-day levels on real-time clinical decision-making. 1. A patient on clozapine is medically admitted to the emergency department (ED), a clozapine blood level assists in distinguishing recent adherence status and impact of health on clozapine level; as a consequence, it may be possible for the patient to continue taking clozapine avoiding the risk of mental health relapse. 2. A patient experiences positive or negative symptoms on their maintenance dose, a clozapine blood level provides information on recent adherence, adequacy of the current dose indicating whether a dose adjustment or re-titration is indicated; the possibility of a dose adjustment would preclude re-titration and the risk of relapse. 3. A patient with TRS has reached 200 mg/d on clozapine titration but has not improved as expected; blood levels could indicate the dose could be safely increased, allowing a safe trial of clozapine, the only effective treatment for TRS.