title: Effects of single intravenously administered doses of omeprazole and ranitidine on intragastric pH and plasma gastrin concentration in nonfed ponies.
abstract: We investigated the effects of a range of IV administered doses of omeprazole (0.125 to 2.0 mg/kg of body weight) on gastric pH (monitored by indwelling electrode) and plasma gastrin concentration, compared with those of IV administered ranitidine (1.0 mg/kg) in 4 Welsh mountain-type ponies. Pharmacokinetic variables of IV administered omeprazole also were examined. Episodes of high gastric pH in the basal state obscured the effect of acid suppression on intragastric pH; however, omeprazole induced dose-dependent increase in mean gastric pH (P < 0.01) during the 11 hours after its administration. In the presence of acid-suppressant treatment, plasma gastrin concentration correlated significantly with gastric pH (Spearman's rank correlation coefficient, rho = 0.445, P < 0.01), whereas basal pH and plasma gastrin concentration were not correlated. The effect was not great, and a dose-dependency was not found. Intravenously administered omeprazole was subject to two-compartment pharmacokinetics, and there was evidence for saturable steps in the redistribution and elimination phases. Dosage of 0.25 mg/kg induced approximately half-maximal inhibition of basal gastric pH in these ponies and was associated with area under the concentration vs time curve of 0.7 mumol.h/L, which corresponds reasonably with results of other species. Omeprazole may represent a useful alternative acid-suppressant agent in horses, but further work is required to relate the dose-dependent effects found in this study to well-defined targets of acid suppression in clinical cases.
authors.affiliation: Department of Large Animal Medicine and Surgery, Royal Veterinary College, University of London, Hatfield, Hertfordshire, England.
authors.forename: S J
authors.initials: SJ
authors.lastname: Baker
authors.forename: E L
authors.initials: EL
authors.lastname: Gerring
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005215:Fasting; D005260:Female; D005745:Gastric Acidity Determination / Q000662:veterinary; D005750:Gastric Juice / Q000187:drug effects / Q000502:physiology*; D005755:Gastrins / Q000097:blood*; D006736:Horses; D006863:Hydrogen-Ion Concentration; D007275:Injections, Intravenous; D009853:Omeprazole / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D011899:Ranitidine / Q000008:administration & dosage / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D005755:Gastrins; D011899:Ranitidine; D009853:Omeprazole