Effect of cimetidine and antacids on gastrointestinal absorption of tetracycline

In a randomized crossover study, five normal subjects were given 250‐mg capsules of tetracycline at weekly intervals with cimetidine 300 mg, sodium bicarbonate 2 gm in water, magnesium–aluminium hydroxide gel 30 ml, or water alone. Gastric pH was monitored by radiotelemetry. Antibiotic bioavailability as measured by area under the serum level–time curve, peak serum level, and urinary elimination was not affected by cimetidine or sodium bicarbonate. Magnesium–aluminum hydroxide gel reduced bioavailability by 90%. The data show that gastric pH does not affect absorption of oral tetracycline and that cimetidine can be used in place of antacids to control gastric acid in patients using tetracycline. Clinical Pharmacology and Therapeutics (1980) 28, 203–207; doi: