The kinetics of citalopram: single and multiple dose studies in man

The kinetics of citalopram were studied in a group of volunteers after oral (8 subjects) and intravenous (4 subjects) single doses and repeated oral administration (7 subjects). Inter- and intraindividual variation was limited and linearity of kinetics indicated. Systemic and apparent oral clearance estimates (mean 0.42 l plasma/min.) were similar, indicating roughly complete systemic availability. The presence of unchanged drug in urine, corresponding to 1/7 of the dose, suggests elimination by renal as well as hepatic processes. The data from the intravenous test revealed two compartment kinetics; the total volume of distribution was estimated to about 1150 l and that of the central compartment to 175 l. Upon repeated administration steady-state conditions were generally achieved after one week in agreement with the 33 hrs half-life of elimination. Citalopram peak concentrations were reached within 2-4 hours after the daily dose and maximally two-fold variation was recorded in the 24 hrs dose interval. The levels of a main pharmacodynamically active metabolite were roughly half as high as the drug levels.