In vitro metabolism of citalopram by monoamine oxidase B in human blood

The metabolism of the antidepressant citalopram (CIT) by monoamine oxidase B (MAO-B) was studied in vitro. In incubations with blood of nine healthy v olunteers R-(P = 0.015) and S-(P = 0.0034) CIT propionic acid (CITPROP) pro duction was correlated with the number of platelets. S-CITPROP production w as 5.6 times higher than R-CITPROP production and in incubations containing the MAO-B inhibitor deprenyl, racemic CITPROP production was diminished to 9.1%. To our knowledge, this is the first time that MAO-B activity in bloo d is shown with an antidepressant as substrate. As MAO is strongly expresse d in human brain, this observation suggests that this enzymatic system may be implicated in drug metabolism in the CNS. (C) 2001 Elsevier Science B.V. All rights reserved.