Effect of cimetidine on absorption of oral tetracycline in mice

Gastric administration of cimetidine, 5 mg/kg, and magnesium aluminum hydroxide gel (Maalox®), 1 ml/kg, were equally effective in raising the gastric pH of mice from 2.5 to 5.0. The antacid depressed by 75% gastrointestinal absorption of tetracycline given by gastric tube at 25 mg/kg. Antibiotic bioavailability was measured by area under the plasma level-time curve, peak plasma level and urinary elimination. Cimetidine did not affect tetracycline absorption as reflected by any of these 3 parameters. If confirmed with the solid dosage form in man, the present study suggests that unlike magnesium aluminum hydroxide gel, cimetidine may be used as an effective means of reducing gastric acid in patients who take tetracycline.