title: Pharmacokinetics and pharmacodynamics of dexamethasone after oral administration in apparently healthy horses.
abstract: OBJECTIVE
  To assess pharmacokinetic and pharmacodynamic properties of dexamethasone administered PO as a solution or powder, compared with properties of dexamethasone solution administered IV, in apparently healthy horses.
  
  
  METHODS
  6 adult horses.
  
  
  METHODS
  Serum cortisol concentration for each horse was determined before each treatment (baseline values). Dexamethasone (0.05 mg/kg) was administered PO (in solution or powdered form) or IV (solution) to horses from which feed had or had not been withheld (unfed and fed horses, respectively). Each horse received all 6 treatments in random order at 2-week intervals; PO and IV administrations of dexamethasone were accompanied by IV or PO sham treatments, respectively. Plasma dexamethasone and serum cortisol concentrations were assessed at predetermined intervals.
  
  
  RESULTS
  Maximum plasma dexamethasone concentration after PO administration of powdered dexamethasone in unfed horses was significantly higher than the maximum plasma concentration after PO administration of dexamethasone solution in unfed or fed horses. Mean bioavailability of dexamethasone ranged from 28% to 66% but was not significantly different among horses receiving either formulation PO in the unfed or fed state. After dexamethasone treatment PO or IV, serum cortisol concentrations were significantly less than baseline at 1 to 72 hours in unfed horses and at 2 to 48 hours in fed horses.
  
  
  CONCLUSIONS
  PO or IV administration of dexamethasone resulted in suppression of cortisol secretion in unfed and fed adult horses; the magnitude of suppression did not differ among treatment groups, and serum cortisol concentrations returned to baseline after 48 to 72 hours.
authors.affiliation: Veterinary Medical Teaching Hospital, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506, USA. dr.grady@sapulpaequine.com
authors.forename: Jason A
authors.initials: JA
authors.lastname: Grady
authors.forename: Elizabeth G
authors.initials: EG
authors.lastname: Davis
authors.forename: Butch
authors.initials: B
authors.lastname: Kukanich
authors.forename: Amanda B
authors.initials: AB
authors.lastname: Sherck
mesh_terms: D000284:Administration, Oral; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000097:blood / Q000493:pharmacokinetics / Q000494:pharmacology; D019540:Area Under Curve; D002940:Circadian Rhythm / Q000187:drug effects; D003907:Dexamethasone / Q000097:blood / Q000493:pharmacokinetics* / Q000494:pharmacology*; D005260:Female; D006207:Half-Life; D006736:Horses / Q000502:physiology*; D006760:Hospitalization; D006762:Hospitals, Animal; D006854:Hydrocortisone / Q000097:blood*; D007700:Kinetics; D008297:Male; D009919:Orchiectomy
chemical_list: D000893:Anti-Inflammatory Agents; D003907:Dexamethasone; D006854:Hydrocortisone