Therapeutic Drug Monitoring of Second-Generation Antipsychotics for the Estimation of Early Drug Effect in First-Episode Psychosis: A Cross-sectional Assessment.

BACKGROUND: Studies on therapeutic drug monitoring (TDM) of second-generation antipsychotics (SGAs) have provided conflicting results regarding the association between dose, plasma concentrations, and drug effect and have focused rather on analyzing how individual drugs work. No study has attempted to process data from different SGAs globally to offer a panoramic view of the utility of TDM in clinical practice, and data on patients with first-episode psychosis (FEP) are lacking. This study aimed to assess the relationship between dose, plasma concentrations, and drug effect in a sample of patients with FEP, regardless of the SGA prescribed.

METHODS: Data from 64 compliant patients treated with the same SGA during a 2-month follow-up were recorded. Clinical symptoms were assessed using the Positive and Negative Symptoms Scale and the Montgomery-Åsberg Depression Rating Scale. Adverse effects were rated using the Udvalg für Kliniske Undersogelser scale. SGA doses were standardized to chlorpromazine equivalents, and patients were classified into 3 different ranges according to their plasma concentrations (subtherapeutic, therapeutic, and supratherapeutic).

RESULTS: Plasma concentration ranges were proportionally related to dose. Patients with supratherapeutic plasma concentrations were treated with doses significantly higher than those with subtherapeutic concentrations. Dose and plasma concentrations were not associated with early drug effect.

CONCLUSIONS: TDM seems unable to accurately estimate the early effects of SGAs in FEP. Ours is the first study to categorize plasma concentrations of SGAs into ranges for joint processing of data from a larger number of patients.