Prolonged influence of a meal on the effect of ranitidine.

Ten healthy volunteers received 150 mg ranitidine or placebo. Eight hours after drug administration they were served a standard meal or continued fasting. Four hours later the gastric acid and pepsin secretion and gastrin and ranitidine levels in blood were recorded for a further 2 h. At the time when secretion was measured, the meal neither stimulated acid or pepsin secretion nor altered the circulating plasma levels of ranitidine or gastrin. In spite of that, the meal significantly reduced the acid-inhibitory effect of ranitidine from 63% to 39% (p less than 0.01). Pepsin secretion was not affected by the meal or the administration of ranitidine. The results indicate that a meal may decrease the acid-inhibitory effect of the H2-receptor antagonist longer than it stimulates acid secretion.