A review of a recently published guidelines' “strong recommendation” for therapeutic drug monitoring of olanzapine, haloperidol, perphenazine, and fluphenazine

INTRODUCTION: In addition to clozapine, there is a growing body of evidence that supports therapeutic drug monitoring (TDM) for additional antipsychotics commonly used in the United States. METHODS: The Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) published TDM guidelines for several psychiatric medications. Sources were identified that the authors used to establish therapeutic reference ranges for haloperidol, fluphenazine, perphenazine, and olanzapine—4 antipsychotics commonly used in the United States with a “strong recommendation” for TDM. The sources were then reviewed for content and appropriateness for utilization in establishing the reference ranges. RESULTS: Olanzapine had 15 citations, haloperidol had 9, perphenazine had 4, and fluphenazine had 2. The studies' methods were reviewed along with the proposed therapeutic reference ranges. DISCUSSION: Several limitations of the guidelines were identified. Reference ranges were suggested based on studies of patients with various diagnoses; some patients had an acute exacerbation, and others were in a maintenance phase. An additional publication was identified that reviewed similar (and additional) TDM studies; those conclusions were in slight contrast with those of the AGNP guidelines. In the future, guidance should be given to those looking to conduct TDM studies to standardize methods and make meta-analysis of this data more feasible.