title: Pharmacokinetics of erythromycin ethylsuccinate after intragastric administration to healthy foals.
abstract: Plasma concentrations and pharmacokinetics of erythromycin and related compounds were determined after administration of erythromycin ethylsuccinate to six healthy male foals 3 to 5 months of age. Hay was withheld from the foals overnight and erythromycin ethylsuccinate (25 mg/kg of body weight) was administered intragastrically. Plasma erythromycin concentrations were determined at specific times after drug administration by high-performance liquid chromatography assay. Maximum peak plasma concentrations, time to maximum concentrations, area under plasma concentration versus time curves, elimination half-life, and mean residence time were determined from concentration versus time curves. Maximum peak concentration of erythromycin A (0.45 +/- 0.27 microg/ml) after administration of erythromycin ethylsuccinate was observed at 2.38 +/- 1.54 hours after treatment. Concentrations of anhydroerythromycin A were maximal at 2.2 +/- 2.0 hours and reached a maximum of 2.6 +/- 1.9 microg/ml. Plasma concentrations of the ester parent drug (erythromycin ethylsuccinate) were below the limit of quantitation (0.1 microg/ml) at all times except 2.5, 2.75, and 5.5 hours. Levels at those times ranged from 0.1 to 0.144 microg/ml. Erythromycin ethylsuccinate appears to be poorly absorbed after oral administration to fasted foals. Plasma concentrations of erythromycin A remained below 0.25 microg/ml (reported minimum inhibitory concentration for Rhodococcus equi) for less than 4 hours after intragastric administration of erythromycin ethylsuccinate, suggesting that the recommended dosage (25 mg/kg every 6 hours) would be suboptimal for treatment of R. equi infections.
authors.affiliation: University of Missouri-Columbia, College of Veterinary Medicine, Department of Veterinary Medicine and Surgery, Columbia, MO 65211, USA.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Lakritz
authors.forename: W David
authors.initials: WD
authors.lastname: Wilson
authors.forename: Antoinette E
authors.initials: AE
authors.lastname: Marsh
authors.forename: Judy E
authors.initials: JE
authors.lastname: Mihalyi
mesh_terms: D000042:Absorption; D000284:Administration, Oral; D000818:Animals; D000833:Animals, Suckling; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D019540:Area Under Curve; D015643:Erythromycin Ethylsuccinate / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D006736:Horses / Q000097:blood*; D008297:Male
chemical_list: D000900:Anti-Bacterial Agents; D015643:Erythromycin Ethylsuccinate