Pharmacokinetics of ranitidine in quadriplegics

In a previous study we observed that quadriplegic patients were unresponsive to ranitidine given in high dose (600 mg day-1 intravenously) for prophylaxis of stress ulceration. The pharmacokinetics of 100 mg of intravenous ranitidine have therefore been studied in six male quadriplegic patients. Plasma drug concentrations declined in a biexponential fashion. The mean (+/- s.e. mean) distribution half-life was 9.42 (+/- 1.04) min. The terminal plasma elimination half-life 1.79 (+/- 0.12) h, the volume of distribution 103 (+/- 17) litres and total body clearance 663 (+/- 86) ml/min. These values are similar to those described in two published studies performed in normal male volunteers. This suggests that there is no pharmacokinetic reason for the quadriplegics to be resistant to ranitidine and the defect is likely to be related to vagal control of acid secretion.