Effect of Calcium and Antacids on Phenytoin Bioavailability

To the Editor.—  We read with interest the article by Chapron et al entitled "Effect of Calcium and Antacids on Phenytoin Bioavailability" (36:436-438, 1979) because we have just completed a similar experiment with different results.We used more subjects, equal neutralizing capacities of antacids rather than equal volumes,¹ a different dose of phenytoin, and gave the antacids in the recommended dosage schedule for peptic ulcer.²Each of eight subjects served as his own control. We randomly assigned the subjects to receive 600 mg of phenytoin alone or with 160 mEq of aluminum hydroxide-magnesium hydroxide gel, calcium carbonate, or aluminum hydroxide-magnesium trisilicate, administered one and three hours after meals and at bedtime. Each subject received phenytoin alone twice and phenytoin plus each of the antacids. Samples were analyzed by the EMIT system,^3.4 and absorption was determined by using the trapezoidal rule to calculate area under the curve (AUC).