The pharmacokinetics and dose proportionality of mosapride citrate ((+-)-4-amino-5-chloro-2-ethoxy-N-[[4- (4-fluorobenzyl)-2-morpholinyl]methyl]benzamide citrate dihydrate, AS-4370, CAS 112885-42-4) were investigated in healthy male volunteers. The subjects were given a single oral dose (5, 10, 20 and 40 mg, each of 5 subjects) and a multiple oral dose (20 mg t.i.d. for one day, and 10 and 20 mg t.i.d. for 8 days, each of 5 subjects). Food effect on the pharmacokinetics of mosapride was also evaluated after a single oral 10 mg dose by an open, two-way crossover method. Mean plasma levels of mosapride reached a peak 0.5-1 h after single dosing of 5, 10, 20 and 40 mg. The peaks were dose-related with values of 25.1, 51.2, 157.8 and 280.6 ng/ml, respectively, and were followed by a first-order decrease with apparent half-lives of 1.4-2.0 h. The Cmax and AUC increased in proportion to the dose, indicating linear pharmacokinetics of mosapride up to 40 mg. The Cmax of M-1, a des-4-fluorobenzyl metabolite, was 1/6 of that of the unchanged drug. Urinary excretion of the unchanged mosapride and M-1 during 48 h after single dosing accounted for 0.1-0.4% and 7.0-11.0% of the dose, respectively. There were no significant changes in the plasma concentration-time profiles and urinary excretions between single and multiple doses, indicating that the pharmacokinetics of mosapride in man was not altered by its multiple administration. Plasma levels of mosapride reached steady state on day 2 of multiple administration.(ABSTRACT TRUNCATED AT 250 WORDS)