Serum Concentrations of Gastrin after Famotidine and Omeprazole Administration to Dogs

Background: The duration of antacid-induced hypergastrinemia after cessation of administration of omeprazole and famotidine apparently has not been determined in dogs. Hypothesis: That serum gastrin will return to basal concentrations by 7 days after cessation of famotidine or omeprazole administration. Animals: Nine healthy, adult, male, research colony dogs. Methods: Randomized, cross-over design. Serum gastrin was determined daily for 7 days to establish baseline concentrations. Famotidine (1.0 mg/kg q24h) or omeprazole (1.0 mg/kg q24h) was administered PO for 7 days followed by a 14-day washout. Serum concentrations of gastrin were determined daily during 7 days of administration and daily for 7 days after cessation of administration. Each drug was evaluated in 8 of the 9 dogs. Results: Omeprazole caused a significant increase in serum gastrin concentration (37.2 +/- 7.3 to 71.3 +/- 19.0 ng/L; P=.006). Famotidine induced a transient increase in serum gastrin (37.2 +/- 7.3 to 65.5 +/- 38.5 ng/L; P=.02) that peaked at administration day 3 and declined thereafter. By day 7 after cessation of both drugs, there was no difference in serum gastrin concentrations compared to those before administration (famotidine P=.99; omeprazole P=.99). During or after administration, gastrin concentrations above 3 times the upper reference range were rare (12 of 224 samples). Conclusions and Clinical Importance: A 7-day withdrawal from short-term administration of famotidine or omeprazole is sufficient for serum gastrin to return to baseline concentrations. Withholding famotidine or omeprazole for longer before investigating pathologic causes of hypergastrinemia is unnecessary.