Erythromycin: Pharmacokinetics, Bioavailability, Nonantimicrobial Activity, and Possible Mechanisms Associated with Adverse Reactions

The oral administration of crushed enteric-coated tablets of erythromycin base to foals suppressed the pulmonary inflammatory response induced by bronchoalveolar lavage. The systemic bioavailability of erythromycin base was low and variable (19.8 6 8.8%), likely as a result of degradation of a substantial portion of the administered dose to microbiologically inactive anhydroerythromycin in the stomach. Anhydroerythromycin may be capable of modulating inflammation and may be responsible for some of the adverse effects observed in foals treated with erythromycin. Erythromycin estolate appears to have a therapeutic advantage over erythromycin base in that its substantially higher bioavailability in foals results in higher plasma concentrations of active erythromycin and lower concentrations of the potentially harmful acid degradation product. Authors’ addresses: Depts. of Molecular Biosciences (Lakritz) and Medicine and Epidemiology (Wilson), School of Veterinary Medicine, University of California at Davis, Davis, CA 95616. r 1997 AAEP.