Therapeutic Drug Monitoring of Venlafaxine: A Systematic Review and Meta-analysis on Concentration–Response Relationship in Depression

Abstract

Venlafaxine is a widely prescribed antidepressant belonging to the class of selective serotonin and norepinephrine reuptake inhibitors. Clinical guidelines recommend therapeutic drug monitoring (TDM) to optimize venlafaxine therapy by measuring its active moiety (AM), which includes venlafaxine (VEN) and its active metabolite O-desmethylvenlafaxine (ODV). However, the clinical utility of TDM depends on the presence of a clear relationship between drug concentration and therapeutic response. The present study aimed to evaluate the association between venlafaxine plasma concentrations, therapeutic efficacy, and adverse drug reactions in patients with depression. A systematic review and meta-analysis were conducted using four electronic databases including MEDLINE (PubMed), PsycINFO, Web of Science Core Collection, and the Cochrane Library. Relevant studies published up to March 2022 were screened according to predefined criteria and critically evaluated. A total of 68 studies met the inclusion criteria. Several cohort studies demonstrated a positive association between higher blood concentrations of venlafaxine and improved antidepressant response. Meta-analysis indicated that responders showed higher concentrations of the active moiety and O-desmethylvenlafaxine compared with non-responders. A linear relationship between daily dose and active moiety concentration was observed within the recommended dosage range of 75–225 mg/day. Based on available evidence, a therapeutic reference range of 140–600 ng/ml for the active moiety (VEN + ODV) is suggested to optimize treatment outcomes while minimizing adverse drug reactions

Keywords

Introduction

Depression is one of the most common psychiatric disorders worldwide and represents a major public health concern due to its significant impact on quality of life and overall health outcomes. Pharmacological treatment plays a crucial role in the management of depression, with antidepressant medications targeting neurotransmitter systems in the central nervous system.Venlafaxine is a selective serotonin and norepinephrine reuptake inhibitor (SNRI) widely used for the treatment of major depressive disorder and other psychiatric conditions. Following administration, venlafaxine undergoes hepatic metabolism to form its active metabolite O-desmethylvenlafaxine, and together these compounds constitute the active moiety responsible for its therapeutic effect.Therapeutic drug monitoring has been proposed as an effective strategy to optimize antidepressant therapy by measuring drug concentrations in biological fluids and adjusting doses accordingly. However, the effectiveness of this approach depends on the presence of a clear relationship between plasma drug levels and clinical response. Although venlafaxine is widely prescribed, evidence regarding its concentration–response relationship remains limited and inconsistent. Therefore, systematic evaluation of available data is required to determine an optimal therapeutic concentration range.

Objective

The present study aimed to investigate the relationship between venlafaxine plasma concentrations, therapeutic efficacy, and adverse drug reactions through a systematic review and meta-analysis. In addition, the study sought to determine an optimal target concentration range for venlafaxine oral formulations in the treatment of depression and to highlight the clinical significance of therapeutic drug monitoring in improving patient outcomes.

Methods

A systematic review and meta-analysis were conducted to identify studies evaluating the relationship between venlafaxine plasma concentrations, treatment efficacy, and adverse drug reactions. A comprehensive literature search was performed using four electronic databases: MEDLINE (PubMed), PsycINFO, Web of Science Core Collection, and the Cochrane Library. The search was carried out in March 2022 according to a predefined protocol. Relevant studies were identified using appropriate keywords related to venlafaxine, therapeutic drug monitoring, antidepressant response, and plasma drug concentrations. All retrieved articles were independently screened by reviewers to determine eligibility based on predefined inclusion and exclusion criteria. Data extraction was conducted systematically, and the methodological quality of the included studies was critically assessed.

RESULTS

The systematic search identified 68 studies that met the predefined eligibility criteria. Most of the included studies were naturalistic therapeutic drug monitoring investigations or small observational studies, while high-quality randomized controlled trials specifically examining the concentration–response relationship were not identified.Among the included studies, five cohort studies demonstrated a positive association between venlafaxine blood concentrations and antidepressant response. Meta-analysis revealed that patients responding to venlafaxine therapy had significantly higher concentrations of the active moiety and O-desmethylvenlafaxine compared with non-responders.A concentration-dependent adverse effect, particularly tremor, was reported in association with higher active moiety concentrations. Additionally, a linear relationship between daily venlafaxine dose and active moiety concentration was observed within the recommended dosage range of 75–225 mg/day.Population-based data from 11 studies involving approximately 3200 patients showed interquartile concentration ranges of 225–450 ng/ml for the active moiety and 144–302 ng/ml for O-desmethylvenlafaxine. Furthermore, one positron emission tomography study demonstrated that O-desmethylvenlafaxine serum concentrations above 85 ng/ml were associated with approximately 80% serotonin transporter occupancy. Based on these findings, a therapeutic reference range of 140–600 ng/ml for the active moiety is proposed.

CONCLUSION

The findings of this systematic review and meta-analysis highlight the clinical importance of therapeutic drug monitoring in venlafaxine therapy. Monitoring the concentration of the active moiety within the proposed therapeutic range of 140–600 ng/ml may improve treatment response, particularly in patients who do not respond adequately at lower drug concentrations. Dose titration within this range may enhance antidepressant efficacy due to the dual mechanism of action of venlafaxine involving serotonin and norepinephrine reuptake inhibition. However, careful monitoring is required, as higher concentrations may increase the risk of adverse drug reactions. Therefore, individualized dose adjustment guided by therapeutic drug monitoring may improve both the safety and effectiveness of venlafaxine therapy.

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