The purpose of the study is to evaluate the pharmacokinetics, pharmacodynamics and safety of rabeprazole after single and multiple daily administration in infants between the ages of 1 and 11 months, inclusive, with GERD.

This is an open-label (both physician and patient know the name of the study medication), multicenter, Phase I study, consisting of 2 parts. The first part of the study will be nonrandomized, all patients will receive the same dose. In the second part of the study, patients will be randomized (study medication assigned by chance) into 2 dose groups. The purpose of the study is to evaluate the pharmacokinetics, pharmacodynamics (intraesophageal/intragastric pH, clinical global impression, formulation palatability and Gastroesophageal Reflux Disease (GERD) daily symptom diary) and safety of rabrepazole after single and multiple daily administration at 2 dose levels in infants between the ages of 1 and 11 months, inclusive (up to 11 months 29 days), with GERD. As this study is an exploratory assessment of the pharmacokinetics, pharmacodynamics and safety of rabeprazole in infants, no formal hypothesis testing is applied. Safety and tolerability, including monitoring of adverse events, clinical laboratory results, physical examination, vital signs and ECG measurements, will be evaluated throughout the study. Patients will receive rabeprazole sodium as single daily oral doses for 5 successive days as a bead formulation. Patients in the first part of the study will receive single and multiple daily every 24 hours doses of 0.14 mg/kg, using increments of 1 mg dose. Safety and pk data from part 1 of the study will determine the 2 dosages to be studied in part 2 of the study.

Inclusion Criteria:

• Patients who have been treated with, or are currently receiving a proton pump inhibitor (PPI), H2 blockers, or antacids are eligible (as long as they can go off antacids for 24 hours, and PPIs and H2 blockers 3 days prior to dosing, except for cimetidine, which must be discontinued for at least 7 days prior to dosing) and remain off these medications for the treatment period
• Patients who are generally healthy, other than the presence of GERD, with the exception of the following: Patients with stable asthma/reactive airway disease or cystic fibrosis-dependent GERD symptoms on stable treatment regimens or subjects on stable doses of allergy medicines.

Exclusion Criteria:

• Patients who have history of or current clinically significant medical illness including (but not limited to) cardiac arrhythmias or other cardiac disease, hematologic disease, coagulation disorders, lipid abnormalities, diabetes mellitus, renal or hepatic insufficiency, thyroid disease, neurologic or psychiatric disease, infection, or any other illness that the investigator considers should exclude the subject or that could interfere with the interpretation of the study results
• Primary pulmonary or ENT symptoms
• Presence of "warning signals", suggesting cause of vomiting/regurgitation other than GERD
• History of primary esophageal motility disorders or systemic condition affecting the esophagus
• History of eosinophilic esophagitis, persistent milk protein allergy, or allergic gastroenteropathy
• History of or current presence of peptic ulcers
• Current presence of Helicobacer pylori
• Significant arrhythmias.