Ranitidine--pharmacology and clinical use.

Abstract

SUMMARY Ranitidine is a new histamine H2-receptor antagonist which differs in chemical structure from both histamine and cimetidine. Animal studies have shown that it is a potent, specific competitive antagonist with a highly effective inhibitory action upon the release of acid and pepsin in gastric secretion invoked by a wide range of secretory stimulants. Similar pharmacological properties have been shown in man. It has no other measurable pharmacological effect resulting from blockade of histamine H2-receptors, nor does it appear to exert any other biological effects in man. The gastric secretory inhibitory effects of ranitidine are qualitatively similar to those of cimetidine but are 4–9 times more potent on a weight-for-weight basis. The pharmacodynamics and pharmacokinetics are such that by administering ranitidine 150 mg morning and night, effective inhibition of intragastric acidity is achieved. Ranitidine has a greater selectivity of action than cimetidine so avoiding certain unwanted effects such as interference with enzymic degradation of a wide range of drugs metabolised by the liver mixed function oxygenase system, antiandrogenic effects and the propensity to cause confusion in the elderly. In short term treatment of duodenal ulceration, ranitidine 150 mg twice daily relieves symptoms and heals ulcers with an expected rate of approximately 80% over four weeks rising to over 90% during eight weeks of treatment, compared with placebo healing rates of around 30%. Similarly, the gastric ulcer healing rate of 60–70% at four weeks and 85% at three months was superior to placebo rates of 40–50%. In both duodenal and gastric ulcer, responses were similar to those previously reported with cimetidine. Nightly maintenance treatment with ranitidine 150 mg significantly reduces the rate of recurrence in patients with duodenal or gastric ulceration. In reflux oesophagitis, ranitidine 150 mg twice daily for six weeks reduces symptoms, and improves endoscopic appearances. Higher doses of ranitidine have been shown to control patients with the Zollinger-Ellison syndrome resistant to cimetidine. There are some reports of beneficial effects of ranitidine on acute upper gastrointestinal haemorrhage. Administered before anaesthesia, ranitidine decreases the volume and elevates the pH of gastric juice and may reduce morbidity and mortality arising from aspiration pneumonitis.