2-Pyridinylmethylsulfinylbenzimidazoles/administration & dosage; 2-Pyridinylmethylsulfinylbenzimidazoles/pharmacokinetics; Anti-Ulcer Agents/administration & dosage; Anti-Ulcer Agents/pharmacokinetics; Gastroesophageal Reflux/blood; Gastroesophageal Reflux/drug therapy; Infant, Premature/metabolism; Proton Pump Inhibitors/administration & dosage; Proton Pump Inhibitors/pharmacokinetics; 2-Pyridinylmethylsulfinylbenzimidazoles/adverse effects; 2-Pyridinylmethylsulfinylbenzimidazoles/blood; Administration, Oral; Age Factors; Anti-Ulcer Agents/adverse effects; Anti-Ulcer Agents/blood; Aryl Hydrocarbon Hydroxylases/genetics; Cytochrome P-450 CYP2C19; Cytochrome P-450 CYP3A/genetics; Dose-Response Relationship, Drug; Drug Administration Schedule; Female; Gastroesophageal Reflux/diagnosis; Gastroesophageal Reflux/ethnology; Genotype; Half-Life; Humans; Infant; Infant, Newborn; Male; Metabolic Clearance Rate; Pantoprazole; Proton Pump Inhibitors/adverse effects; Proton Pump Inhibitors/blood; Time Factors; Treatment Outcome