The proton pump inhibitor esomeprazole comprises the S-isomer of omeprazole. An intravenous formulation of the drug has been developed for use in patients not able to take oral drugs. The level of gastric acid control was similar with intravenous and oral esomeprazole in two studies in healthy volunteers receiving 20 or 40 mg once daily for 5 days. In addition, a similar level of gastric acid control occurred with intravenous esomeprazole 40 mg administered by infusion or injection once daily for 10 days. In healthy volunteers, intravenous esomeprazole provided faster and more effective gastric acid control than intravenous pantoprazole (40 mg once daily for 5 days). In addition, control of basal and pentagastrin-stimulated gastric acid secretion was better with intravenous esomeprazole 40 mg than with intravenous omeprazole 40 mg (single-dose study). Healing rates at 4 weeks were approximate, equals 80% in a well designed study in patients with erosive oesophagitis (n = 246) who received esomeprazole 40 mg once daily intravenously (by injection or infusion) or orally. Intravenous therapy was administered for the first week, after which all patients received oral esomeprazole. Intravenous esomeprazole was generally well tolerated in patients with erosive oesophagitis, with a tolerability profile similar to that of the oral formulation.