Heterozygous mutation in CYP2C19 significantly increases the concentration/dose ratio of racemic citalopram and escitalopram (S-citalopram).

There is limited documentation of the importance of heterozygous cytochrome P450 (CYP) mutations on drug exposure. This study was designed to evaluate the influence of heterozygous mutations in CYP2C19 on the serum concentration of racemic citalopram and escitalopram (S-citalopram). Eighty-three samples from subjects with determined CYP2C19 and CYP2D6 genotype receiving racemic citalopram or S-citalopram as part of their clinical treatment were collected from a routine therapeutic drug monitoring database.