Ranitidine kinetics in normal subjects.

A 1-mg/kg IV bolus injection and a 150-mg (one tablet) oral dose of ranitidine were given to seven normal subjects. At least 1 wk separated the two doses. Ranitidine disappeared from plasma with a half-life of about 2.5 hr. Half of the oral dose was effectively absorbed and half of the absorbed amount was found unchanged in urine. Total body clearance was 10.1 ml/min/kg. Urinary clearance was the same after oral and intravenous doses (6.4 and 6.9 ml/min/kg, P greater than 0.10). Intravenous ranitidine kinetics included three phases, with a central distribution volume of 0.2 l/kg and a total distribution volume of 1.2 l/kg. Absorption kinetics were apparently order zero: of the 150-mg dose, 75 mg was absorbed during 5 hr at a constant rate of 15 mg/hr.