Scant data exist on the normal range of serum gastrin in infants. In phase I and III trials of rabeprazole in gastroesophageal reflux disease, we studied serum gastrin levels in infants 1 to 11 months old, and assessed normal ranges and the effect of acid-suppressive drugs. Methods: Overall, 349 treatment-naïve or treatment-experienced (previously exposed to proton pump inhibitors and/or H 2 -receptor antagonists) infants with gastroesophageal reflux disease were screened for baseline serum

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... rin. Repeat gastrin was monitored at early termination or end of study, allowing assessment of 1 to 8 week daily rabeprazole (5-or 10-mg) treatment on gastrin levels. Results: Median (5%-95% range) baseline gastrin was 118 ng/L (39-315) in the treatment-naïve group (n ¼ 251), driven mostly by high levels (121.5 [48-326] ng/L) in the 1-to <4-month-old subgroup. Treatmentexperienced infants (n ¼ 98) had elevated baseline gastrin levels (152 [48-487] ng/L; P ¼ 0.0011) with no clear difference between previously proton pump inhibitor-exposed and H 2 -receptor antagonistexposed groups. At the end of study, mean (standard deviation) levels were unchanged from baseline in infants withdrawn from rabeprazole to placebo (124 [94] ng/L), but elevated from baseline in those continuing treatment with 5-mg (245 [151] ng/L) and 10-mg (332 [222] ng/L) rabeprazole during the study. Conclusions: Gastrin levels in treatment-naïve infants were elevated through 8 months of age. Between 8 and 12 months of age, they declined so that the median level was within the upper limit of the normal adult range (<100 ng/L). Previous exposure to acid-suppressive medications and short-term exposure to rabeprazole significantly increased gastrin levels in infants younger than 1 year.