Comparison of the effects of over-the-counter famotidine and calcium carbonate antacid on postprandial gastric acid. A randomized controlled trial

Abstract

Objective: To compare an over-the-counter histamine2-receptor antagonist with an antacid as gastric acid reducers.

Design: Randomized, double-blind, placebo-controlled crossover trial.

Setting: Gastric secretory research laboratory in a Veterans Affairs medical center.

Participants: Eighteen healthy volunteers (10 men and 8 women) aged 25 to 62 years with normal gastric acid secretion rates.

Interventions: The subjects received the histamine2-receptor antagonist famotidine (Pepcid AC, 10 mg), calcium carbonate antacid tablets (Tums, 1000 mg), or placebo medications 1 hour after a test meal. Two identical meals were taken 2.5 and 6.0 hours after the medication was given.

Main outcome measures: Intragastric pH was maintained at 4.0 by in vivo intragastric titration with 0.3N sodium bicarbonate for 10 hours (1 hour before and 9 hours after medication). Reduction in sodium bicarbonate titrant use in the 2 treatment groups compared with titrant use with placebo was reflective of acid secretion inhibited by a famotidine or acid neutralized by calcium carbonate tablets.

Results: When evaluated in increments of 30 minutes, calcium carbonate had a rapid onset of action, neutralizing 6.7 mmol of acid in the first 30 minutes. However, its duration of effect was only 60 minutes. Famotidine had a delayed onset of action compared with antacid, beginning after 90 minutes. However, famotidine had a duration of effect of at least 540 minutes. At its peak effect, 210 minutes after administration, famotidine reduced acid secretion by 7.3 mmol per 30 minutes.

Conclusions: Recommended over-the-counter doses of famotidine and calcium carbonate tablets have different pharmacokinetic profiles when taken in the postprandial period. The antacid has a rapid onset and short duration of action, while the histamine2-receptor antagonist has a delayed onset and a prolonged duration. Their peak potencies are similar.