Escitalopram structure

The selective serotonin re-uptake inhibitors (SSRIs) that are currently available are fluoxetine, fluvoxamine, paroxetine, sertraline, citalopram, and escitalopram. They are widely marketed and are in many countries a major alternative to tricyclic antidepressants in the treatment of depression. The SSRIs are structurally diverse, but they are all inhibitors of serotonin uptake, with much less effect on noradrenaline. They have slight or no inhibitory effect on histaminergic, adrenergic, serotonergic, dopaminergic, and cholinergic receptors (1). 

FIGURE B.3. The chemical structure of citalopram (Celexa), showing its two enantiomers. The S-citalopram enantiomer is escitalopram (Lexapro) (see text). Illustration copyright 2005 by Keren Albala. Used with permission. 

The diversity of the SSRIs is evident not only in their chemical structures, but also in their pharmacokinetic profiles. Fluoxetine has an elimination half-fife of 2 to 3 days (4 to 5 days with multiple dosing). The single-dose hah-hfe of norfluoxetine, the active metabolite, is 7 to 9 days. Paroxetine and sertrahne have half-lives of approximately 24 hours. Unlike paroxetine, sertraline has an active metabolite, but the metabohte contributes minimally to the pharmacologic effects. Escitalopram has a half-life of approximately 30 hours. Peak plasma concentrations of citalopram are observed within 2 to 4 hours after dosing, and the elimination half-life is about 30 hours. The SSRIs, with the exception of fluvoxamine, escitalopram, and citalopram, are extensively bound to plasma proteins (94% to 99%). The SSRIs are extensively distributed to the tissues, and aU, with the possible exception of citalopram, may have a nonlinear pattern of drug accumulation with long-term administration. ... 

Fig. 22.21. Structures of the selective serotonin reuptake inhibitors (SSRIs) fluoxetine, fluvoxamine, paroxetine, sertraline, and escitalopram.

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