title: The effects of dose and diet on the pharmacodynamics of omeprazole in the horse.
abstract: BACKGROUND
  Conflicting data are presented in the current literature regarding the efficacy of omeprazole for suppressing gastric acidity in the horse.
  
  
  OBJECTIVE
  The objective of this study was to investigate the duration of intraday acid suppression achieved with two doses of omeprazole under two different dietary conditions.
  
  
  METHODS
  A four-way crossover design.
  
  
  METHODS
  Six adult Thoroughbred horses instrumented with percutaneous gastrotomy tubes were used. Intragastric pH was measured for continuous 23 h periods (08.00-07.00 h) for six consecutive days (Days 0-5). Baseline data was recorded on Day 0 and omeprazole administered on Days 1-5. Two doses (1 mg/kg and 4 mg/kg bwt per os once a day) and two diets (a high grain/low fibre [HG/LF] and ad libitum hay [HAY)] diet) were studied. Data for the percent (%) time pH was above 4 (%tpH>4) and median intraday pH was reported for two measurement locations and analysed using generalised estimating equations.
  
  
  RESULTS
  An effect of both diet and dose was evident with mean %tpH>4 and the mean of the median intraday pHs typically higher at the higher (4 mg/kg bwt) dose and in HG/LF diet. The overall efficacy of omeprazole in raising intragastric pH was good under the HG/LF conditions but relatively poor in the HAY diet. A cumulative effect of dosing, not previously reported in the horse, was observed.
  
  
  CONCLUSIONS
  The overall efficacy of omeprazole in raising ventral gastric pH was less than previously reported. Both dose and diet may play a role in the efficacy of omeprazole in the horse. Therefore, the use of singular dosing recommendations that encompass all horse types and management conditions may not be appropriate and dosing recommendations that take into account the diet of the horse may be advantageous.
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, Australia.
authors.forename: B W
authors.initials: BW
authors.lastname: Sykes
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, Australia.
authors.forename: C
authors.initials: C
authors.lastname: Underwood
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, Australia.
authors.forename: R
authors.initials: R
authors.lastname: Greer
authors.affiliation: Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, UK.
authors.forename: C M
authors.initials: CM
authors.lastname: McGowan
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, Australia.
authors.forename: P C
authors.initials: PC
authors.lastname: Mills
mesh_terms: D000818:Animals; D000897:Anti-Ulcer Agents / Q000493:pharmacokinetics*; D018592:Cross-Over Studies; D004032:Diet; D004305:Dose-Response Relationship, Drug; D005745:Gastric Acidity Determination; D006734:Horse Diseases / Q000188:drug therapy*; D006736:Horses; D006863:Hydrogen-Ion Concentration; D009853:Omeprazole / Q000493:pharmacokinetics*; D013276:Stomach Ulcer / Q000188:drug therapy / Q000662:veterinary*; D016896:Treatment Outcome
chemical_list: D000897:Anti-Ulcer Agents; D009853:Omeprazole
keywords: gastric; glandular; horse; proton pump inhibitor; squamous; ulcer