Pharmacokinetic correlates of clinical response in a naturalistic sample of escitalopram-treated patients.

OBJECTIVE

We assessed pharmacokinetic correlates of treatment response to escitalopram using a large therapeutic drug monitoring database.

METHODS

A large naturalistic sample of patients receiving escitalopram was analyzed. Responders were defined as 'very much improved' or 'much improved' based on the Clinical Global Impression - Improvement score, CGI-I. We compared responders ( = 83) vs. non-responders ( = 388) with the primary outcome being the escitalopram plasma concentration and concentration corrected by the daily dose (C/D ratio). Effects of age, sex, body-mass-index (BMI), and C/D ratio were assessed in a multivariate logistic regression model predicting response.

RESULTS

There were no statistically significant differences in clinical and demographic characteristics between responders vs. non-responders. There were also no differences between escitalopram daily doses or plasma concentrations, while C/D ratios were significantly higher in non-responders than in responders (1.6 ± 1.7 vs. 1.2 ± 0.9 (ng/mL)/(mg/day),  = 0.007); C/D ratios (odds ratio 0.52, 95% confidence interval 0.34-0.80, < 0.003) were associated with response to escitalopram, after controlling for age, sex, and BMI.

CONCLUSIONS

Patients with low clearance of escitalopram as reflected upon high C/D ratios may be less likely respond to escitalopram. Identifying these patients during dose titration may support clinical decision-making, including switching to a different antidepressant instead of increasing daily dose.