Pupillary Changes as a Potential Biomarker for Escitalopram in Relation to CYP2C19 Polymorphism

Overview

To study the impact of CYP2C19 polymorphism on escitalopram pharmacokinetics and pharmacodynamics measured as changes in pupil diameter

Escitalopram, the therapeutic active S-enantiomer of citalopram, is a selective serotonine reuptake inhibitor (SSRI) used for treatment of depression and anxiety disorders. The antidepressant effect is probably due to a stimulation of the serotonergic neurotransmission caused by the inhibition of the presynaptic serotonin reuptake. This inhibition may also be responsible for the increased pupil diameter seen in volunteers treated with racemic citalopram. Based on escitaloprams pharmacodynamic properties it is expected to have the same affect on pupil diameter. A dose/response relationship has not yet been established but theoretically the pupillary changes might serve as a biomarker for the serotonergic effect of escitalopram. Escitalopram is demethylated in part by the polymorphic cytochrome P450 enzyme 2C19 (CYP2C19); but the impact of CYP2C19 polymorphism on the total metabolism of escitalopram is still to be investigated. Objective: The aim of this study is to investigate the pharmacokinetics and pharmacodynamics in CYP2C19 extensive metabolizers (EMs) and poor metabolizers (PMs) and to investigate whether change in pupil size reaction to a light stimulus can act as a biomarker for the serotonergic effect of escitalopram. The study will be conducted as a randomized, double blinded; placebo controlled two phases cross-over trial with single and repeated doses of 20 mg escitalopram and equivalent placebo. Sixteen healthy volunteers (8 EMs and 8 PMs) will participate in the trial. Prior to the trial, approximately 400 volunteers will be phenotyped by omeprazole metabolic ratio in order to identify the CYP2C19 EMs and PMs. During the two phases blood samples will be drawn and pupil sizes will be measured at fixed time points after drug administration.

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Outcomes