No Influence of Body Weight on Serum Levels of Antidepressants

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Body weight may affect pharmacokinetic parameters in various ways and may therefore have a significant impact on the serum concentration of a drug at a given dose. Although patients with major depressive disorder frequently show an elevated body mass index, studies investigating the relation between body weight and serum concentration of antidepressants are lacking. This study should help to clarify the influence of body weight on the serum levels of the antidepressants amitriptyline (AMI), clomipramine (CLO), doxepine (DOX), escitalopram (ESC), and venlafaxine (VEN) in a naturalistic clinical setting.


Therapeutic drug monitoring analyses obtained in the psychiatric university hospital of Wuerzburg from patients treated with AMI (n = 171), CLO (n = 94), DOX (n = 133), ESC (n = 19), and VEN (n = 24) were retrospectively assessed. The influence of body weight on dose-corrected serum concentrations was evaluated by Spearman-Rho correlations and by comparing dose-corrected serum levels in patients with low and high body weight (first versus fourth quartile). The serum concentrations were determined by high-performance liquid chromatography methods in the therapeutic drug monitoring laboratory of the psychiatric university hospital of Wuerzburg.


Dose-corrected serum concentrations did not significantly correlate with body weight in patients treated with AMI, CLO, DOX, ESC, or VEN. There was no significant difference in the dose-corrected serum concentrations of AMI, CLO, and DOX between patients of the first and fourth quartiles of body weight. The latter evaluation was not performed for ESC and VEN because of too small samples.


Against the intuitive presumption of a weight dependency of dose-corrected serum concentrations, the findings suggest that there is no relevant influence of body weight on the dose-corrected serum level of several widely used antidepressants even if extreme subgroups of patients with low and high body weights are considered.

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