1. Intragastric pH monitoring was performed before and after the single-blind administration of ranitidine or placebo (saline) in eight healthy subjects and four patients with end-stage renal disease who were on regular haemodialysis.
2. The subjects were studied on two occasions and were given aluminium hydroxide (1185 mg) orally 90 min after the administration of ranitidine or saline.
3. Plasma aluminium concentrations and, in normal men, urinary excretion of aluminium were monitored before and after the oral aluminium load.
4. Intragastric pH increased significantly with ranitidine but not with placebo (P < 0.001). Urinary aluminium excretion increased significantly after the administration of aluminium hydroxide during the placebo phase (P < 0.001) but not during the ranitidine phase. Plasma aluminium concentrations were higher in the patients with renal failure than in the normal subjects (P < 0.05), but were unchanged in both groups after the oral aluminium load.
5. This study shows that gastric pH is an important factor in the modulation of aluminium absorption in man, and indicates that reducing gastric acid secretion with ranitidine may reduce the toxicity of orally administered aluminium compounds.