Oxytetracycline Levels in Healthy and Diseased Calves

Abstract

This project was designed to investigate the effects of disease on the tissue concentrations, serum concentrations, and pharmacokinetics of oxytetracycline (OTC) in pneumonic calves.  In reviewing the results of this study it is apparent that there was a poor correlation between serum concentrations and tissue concentrations at 24 hours at this dose (Table I). If the tissue:serum concentration ratios are examined, it is obvious that the serum concentrations were poor predictors of tissue concentrations at this time. The tissue levels varied from 2 to IO times greater than the concurrent serum concentration. If the ratios for the diseased lung are compared to those of the healthy lung it can be seen that the serum concentrations as predictors of tissue concentrations was even more variable in diseased animals. The 24 hour tissue concentrations were considerably higher (2. 96 times) than the 24 hour serum concentrations. This raises a question regarding redosing of OTC at 12 or 24 hours based on declining serum concentrations.