Wilson RC, Huber TL & Goetsch DD
Serum erythromycin concentration in sheep fed two diets.

Am J Vet Res, 45(6): 1148-1150, 1984
ISSN: 0002-9645 American Journal of Veterinary Research (PubMed)

Abstract
Serum erythromycin concentrations following a single IV injection (12.5 mg/kg) were compared in 6 sheep during feeding of a grass hay diet and a concentrate diet. The concentrate diet resulted in a mean decrease of at least 1 pH unit in forestomach fluid, but did not significantly alter either the serum drug concentrations or half-life. Variable antibacterial activity was present in forestomach fluid as early as 1 or 2 hours after injection. This study indicates that ion-trapping in forestomach fluid as a result of normal dietary changes does not require therapeutic dosage adjustment.