title: Pharmacokinetics of erythromycin estolate and erythromycin phosphate after intragastric administration to healthy foals.
abstract: OBJECTIVE
  To determine pharmacokinetics and plasma concentrations of erythromycin and related compounds after intragastric administration of erythromycin phosphate and erythromycin estolate to healthy foals.
  
  
  METHODS
  11 healthy 2- to 6-month-old foals.
  
  
  METHODS
  Food was withheld from foals overnight before intragastric administration of erythromycin estolate (25 mg/kg of body weight; n = 8) and erythromycin phosphate (25 mg/kg; 7). Four foals received both drugs with 2 weeks between treatments. Plasma erythromycin concentrations were determined at various times after drug administration by use of high-performance liquid chromatography. Maximum plasma peak concentrations, time to maximum concentrations, area under plasma concentration versus time curves, half-life of elimination, and mean residence times were determined from concentration versus time curves.
  
  
  RESULTS
  Maximum peak concentration of erythromycin A after administration of erythromycin phosphate was significantly greater than after administration of erythromycin estolate (2.9 +/- 1.1 microg/ml vs 1.0 +/- 0.82 microg/ml). Time to maximum concentration was shorter after administration of erythromycin phosphate than after erythromycin estolate (0.71 +/- 0.29 hours vs 1.7 +/- 1.2 hours). Concentrations of anhydroerythromycin A were significantly less 1 and 3 hours after administration of erythromycin estolate than after administration of erythromycin phosphate.
  
  
  CONCLUSIONS
  Plasma concentrations of erythromycin A remained > 0.25 microg/ml (reported minimum inhibitory concentration for Rhodococcus equi) for at least 4 hours after intragastric administration of erythromycin phosphate or erythromycin estolate, suggesting that the recommended dosage for either formulation (25 mg/kg, q 6 h) should be adequate for treatment of R equi infections in foals.
authors.affiliation: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis 95616, USA.
authors.forename: J
authors.initials: J
authors.lastname: Lakritz
authors.forename: W D
authors.initials: WD
authors.lastname: Wilson
authors.forename: A E
authors.initials: AE
authors.lastname: Marsh
authors.forename: J E
authors.initials: JE
authors.lastname: Mihalyi
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000097:blood / Q000493:pharmacokinetics*; D019540:Area Under Curve; D002851:Chromatography, High Pressure Liquid / Q000662:veterinary; D004917:Erythromycin / Q000031:analogs & derivatives / Q000097:blood / Q000493:pharmacokinetics*; D004918:Erythromycin Estolate / Q000097:blood / Q000493:pharmacokinetics; D005260:Female; D006207:Half-Life; D006736:Horses / Q000502:physiology*; D016018:Least-Squares Analysis; D011897:Random Allocation; D018709:Statistics, Nonparametric
chemical_list: D000900:Anti-Bacterial Agents; C010948:erythromycin lactobionate; D004917:Erythromycin; D004918:Erythromycin Estolate