Effects of prior feeding on pharmacokinetics and estimated bioavailability after oral administration of a single dose of microencapsulated erythromycin base in healthy foals.

The research analyzes how the timing of feeding affects the absorption and effectiveness of a single dose of orally administered microencapsulated erythromycin (an antibiotic) in young horses. It was found that administering the antibiotic to horses on an empty stomach results in a more effective absorption rate as opposed to when the horses have been fed beforehand.

Methodology

• The study was conducted on 6 healthy foals aged between 3 to 5 months old.
• The foals were administered two doses of microencapsulated erythromycin base (MEB), each dose consisting of 25 mg per kg of body weight.
• As part of the crossover design of the study, one dose was given after food was withheld overnight (the foals were essentially fasting), while the other was administered after the foals had eaten hay.
• A two-week period between doses was allowed for.
• The researchers collected blood from the jugular vein of the horses before and at specific intervals after the administration of the drug.
• High performance liquid chromatography was the method utilized to determine the levels of erythromycin A and its derivative, anhydroerythromycin A, in the plasma of the foals.

Results

• In comparing the pharmacokinetic data (the way the drug moves within the body) for both the fed and unfed conditions for the horses, the study discovered that the plasma concentrations of erythromycin A were lower when the foals were fed before being given the drug.
• Furthermore, data showed that the area under the plasma concentration-time curve, the maximum plasma concentration, and the estimated bioavailability of the drug were all greater when the horses were not fed before drug administration.
• All foals showed traces of anhydroerythromycin A (a breakdown product of erythromycin) in their plasma after administration of MEB.

Conclusion

• The study concludes that in order for the MEB to be more effective, it should be given to foals before they are fed hay.
• Withholding food overnight before giving the medication results in plasma concentrations of erythromycin A that are above the minimum required to inhibit the growth of Rhodococcus equi (a bacterium that causes pneumonia in foals) for approximately 5 hours.
• A dosage of 25 mg per kg body weight every 8 hours, orally, is recommended as a result of the findings of the study.