Correlation between tissue and plasma concentrations of oxytetracycline in veal calves.

Mercer et al. (1977) proposed a three-phase experimental design to establish withdrawal times, based on plasma pharmacokinetics. This approach was the premise of a study in which plasma pharmacokinetics and tissue depletion data of oxytetracycline after intramuscular administration were correlated. Correlations between estimated and measured concentrations were shown to be significant for kidney tissue (r = .9236, p < .001), liver tissue (r = .9302, p < .01) as well as for muscle tissue (r = .9045, p < .001). The data presented support the pharmacokinetic approach as proposed by Mercer et al. (1977) and demonstrate that tissue elimination rates correlate highly with elimination rates in plasma. Although generalizations must be applied with caution, this article shows that when certain criteria are fulfilled, plasma pharmacokinetics can reliably predict tissue withdrawal times.