Chronic suppression of gastric acid secretion by histamine2-receptor antagonists (H2RAs) can lead to increased serum gastrin concentrations in humans and rats. Gastrinoma is a gastrin-secreting endocrine tumor that causes GI and other signs in dogs. H2RAs are commonly prescribed for GI signs in dogs but might interfere with diagnosis of gastrinoma by falsely increasing serum gastrin.

This 2-part study examined the effect of famotidine, an H2RA, on serum gastrin concentrations in dogs (part A) and the stability of gastrin samples held at room temperature (part B). In part A, famotidine (0.5 mg/kg PO q12h) was administered to 11 healthy dogs for 14 days. Fasted serum gastrin concentration was measured on days 0, 3, 7, 11, 14, 16, 18, and 22. Results showed serum gastrin levels peaked by day 3 and returned to baseline by day 14. In part B, paired serum samples from 7 dogs were frozen within 30 minutes or kept at room temperature for 150 minutes before being frozen. Serum gastrin concentrations decreased by a mean of 20% when held at room temperature. The authors concluded that long-term famotidine use unlikely contributes to increased serum gastrin concentrations.

Commentary
This study addressed a specific question about whether long-term H2RA therapy can induce hypergastrinemia and interfere with diagnosis of gastrinoma (it does not). However, the study raised other issues: Since serum gastrin concentrations peaked by day 3 and returned to baseline by day 14, further investigation is needed to determine whether prolonged famotidine administration is effective in suppressing gastric acid production. A study simultaneously measuring intragastric pH could determine whether abrupt discontinuation of H2RA after chronic therapy results in rebound acid hypersecretion in dogs, as it does in humans. As with other studies on gastric acid inhibitors: some answers, more questions.—P. Jane Armstrong, DVM, MS, MBA, DACVIM

Source
Normal dogs treated with famotidine for 14 days have only transient increases in serum gastrin concentrations. Mordecai A, Sellon RK, Mealey KL. J VET INTERN MED 25:1248-1252, 2011.