Use of Plasma Levels of Antipsychotics: A Conversation With Jonathan M. Meyer, MD, DLFAPA

TALKING WITH TITANS OF PSYCHOPHARMACOLOGY

At the 2025 American Psychiatric Association (APA) Annual Meeting, Psychiatric Times' Editor in Chief, John J. Miller, MD, sat down with leaders in psychopharmacology to discuss the topics they find most important.

Jonathan M. Meyer, MD, DFAPA, is a prolific writer and the author of several books. As The Clinical Use of Antipsychotic Plasma Levels¹ is Miller's favorite, the 2 sat down to discuss the underutilization of plasma levels of antipsychotics in current practice.

"The difficulty we all run into as practitioners is, if someone is on an oral medication in particular and they are not doing well, how do you know what to do? You are literally guessing. The guess may be wrong. Why would you make guesses or fly blind when you can get information to help guide dosing decisions?" said Meyer.

The turnaround for plasma levels can be slow, as long as 1-2 weeks, Meyer notes. The future, however, could include plasma level turnaround times of merely hours. Quick turnaround times became especially important during the COVID-19 pandemic, as clozapine levels would go up due to acute inflammation during infection. If a patient is not responding as expected when taking antipsychotics, Meyer immediately suggests taking a level.

"We realized that there is a response threshold for every antipsychotic that has been studied, with levels below which you are unlikely to be a responder," said Meyer. "You're titrating someone on a medication and they are not getting better? Why is that? The levels become your friend."

Levels can tell a clinician 3 things about a patient: (1) Is the patient taking their antipsychotic? (2) Is the level high enough that it is time to change to a different antipsychotic? (3) Does this patient metabolize things differently?

"They give you an actionable piece of concrete information that is a bookmark in time that allows you to make a change," said Miller.

Also important to note, more is not better. Meyer shared that, if a patient is not responding to an antipsychotic, continually increasing dose does not mean the patient will respond. "You want to have a target for your initial level if you have a nonresponder. Then, if they do not respond at that target, you want to keep titrating until 1 of a few things happens: (1) The person gets a lot better, (2) The person cannot stand it anymore, or (3) You get to the point of futility," said Meyer.

Meyer concluded with 1 point he would like all clinicians who prescribe antipsychotics to know:

• Do not give antipsychotics multiple times per day. There is no efficacy damage for giving antipsychotics multiple times per day. All you do is incur more adverse effects, especially D2 related. Only clozapine may be an exception.

"Patients with schizophrenia are among the most ill that many of us will ever see. Why would we not want all the information we can gather to make the best decision to help this person?" concluded Meyer.

Dr Meyer is a voluntary clinical professor of psychiatry at the University of California, San Diego.

Dr Miller is Medical Director, Brain Health, Exeter, New Hampshire; Editor in Chief, Psychiatric Times; Voluntary Consulting Psychiatrist at Seacoast Mental Health Center, Exeter/Portsmouth, NH; Consulting Psychiatrist, Insight Meditation Society, Barre, Massachusetts.

References

1. Meyer JM, Stahl SM. The Clinical Use of Antipsychotic Plasma Levels. Cambridge University Press; 2021.

2. Thompson D, Delorme CM, White RF, Honer WG. Elevated clozapine levels and toxic effects after SARS-CoV-2 vaccination. J Psychiatry Neurosci. 2021;46(2):E210–E211.