Pharmacokinetics of erythromycin estolate and erythromycin phosphate after intragastric administration to healthy foals.
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.
Lakritz
J
J
Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis 95616, USA.
Wilson
W D
WD
Marsh
A E
AE
Mihalyi
J E
JE
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
D000900:Anti-Bacterial Agents; C010948:erythromycin lactobionate; D004917:Erythromycin; D004918:Erythromycin Estolate