Kinetics of citalopram in man; plasma levels in patients.

1. Citalopram is rapidly absorbed and slowly eliminated in man. The kinetics is linear and characterized by systemic and apparent oral clearance values of 0.4 l/min, a theoretical distribution volume of 14 l/kg and a half-life of 1 1/2 days. 2. The steady state plasma levels in 70 patients range from 95 to 720 nM at doses of 30 to 60 mg and agree well with predicted values. The mean level is 245 nM at the standard dose of 40 mg daily. 3. Inter-individual variation is 7-fold and independent of sex and age (21-65 years). The average intra-individual variation is about 15%. Estimates of apparent oral clearance vary from 0.15 to 1.02 l/min. 4. The average concentration ratio between citalopram and its demethylated metabolite is 2.7. The levels of di-demethylated metabolite are negligible.