Citalopram: an interaction study with clomipramine in a patient heterozygous for CYP2D6 genotype

A pharmacokinetic interaction between the selective serotonin reuptake inhi bitor citalopram and a tricyclic antidepressant, clomipramine, was noted in a patient treated for major depression and obsessive-compulsive disorder. After the addition of citalopram, a desmethylclomipramine plasma level incr ease and an 8-hydroacy-desmethylclomipramine plasma level decrease were obs erved. The CYP2D6 phenotype, determined when the patient received the antid epressant comedication, characterized a poor metabolizer status (dextrometh orphan metabolic ratio > 0.3), despite a heterozygous genotype containing a wild-type allele with extensive metabolic capacity and a mutant non-functi onal allele (CYP2D6*1A/CYP2D6*4A). This case seems to be one of the first d escriptions of the clinical relevance of a CYP2D6 heterozygous genotype in a patient treated with antidepressant.