Citalopram chemical structure

SSRI medications differ greatly in their chemical structures and composition. For example, citalopram is a tertiary amine with 2 N-metabolites. All three com-... 

Talopram 58 and citalopram 59 (Figure 2.17) are closely related in their chemical structures. Nevertheless, talopram is a norepinephrine uptake blocker with a selectivity factor of about 550 against serotonin uptake, whereas citalopram is a serotonin uptake blocker, with a selectivity of 3400 against norepinephrine uptake. A similar selectivity difference applies to the even more closely related pair nisoxetine 60, with a norepinephrine uptake selectivity of about 180, and fluoxetine 61 (Figure 2.17), with a serotonin uptake selectivity of 54 [33],... 

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. ... 

Figure 2.17 The structural analogs talopram 58 and citalopram 59 (upper compounds), as well as nisoxetine 60 and fluoxetine 61 (lower compounds), are chemically closely related. Whereas 58 and 60 (left compounds) are highly selective norepinephrine uptake inhibitors (selectivity factors of 550 and 180, respectively), the close analogs 59 and 61 (right compounds) are selective serotonin uptake inhibitors (selectivity factors of 3400 and 54, respectively).

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