AABP Executive Director Dr. Fred Gingrich is joined by AABP Past President Dr. Pat Gorden, a professor of dairy production medicine and clinical pharmacology at Iowa State University College of Veterinary Medicine.

 We review the meaning of violative drug residues and the most common medications used in cattle that have historically been associated with violative drug residues. Gorden also reviews both how animals are selected for testing and how withdrawal intervals are determined by drug sponsors when going through the drug approval process. Of particular importance is the effect of disease on the clearance of drugs from the animal since the residue studies are performed on healthy animals for FDA submission.

 Gorden reviews basic pharmacologic mechanisms for drugs and how disease state may impact drug clearance. He also reviews a study he performed that looked at severe clinical mastitis cows and the impact on the pharmacokinetics of ceftiofur in these animals. Veterinarians should utilize FARAD for withdrawal determinations and consider disease state on drug clearance. 

 Finally, Gorden offers suggestions for practicing veterinarians to review with farm managers and employees, including observations in the hospital pen or when treatments are administered. Ensuring correct protocol compliance, applying correct therapy, estimating the correct weight, extending the withdrawal interval on sick animals, ensuring the correct dose, route and volume of injection, and fully mixing suspensions prior to filling the syringe are all important items to check. Veterinarians are tasked with ensuring appropriate oversight on drug use on farms and regularly reviewing these steps is an important aspect of this stewardship principle as well as creating billable hours that are valued by the client.

P.J. Gorden, M.D. Kleinhenz, L.W. Wulf, B. KuKanich, C.J. Lee, C. Wang, J.F. Coetzee, Altered plasma pharmacokinetics of ceftiofur hydrochloride in cows affected with severe clinical mastitis, J Dairy Sci. Volume 99, Issue 1, 2016, Pages 505-514, https://doi.org/10.3168/jds.2015-10239.

Gorden PJ, Ydstie JA, Kleinhenz MD, et al. Comparative plasma and interstitial fluid pharmacokinetics and tissue residues of ceftiofur crystalline-free acid in cattle with induced coliform mastitis. J Vet Pharmacol Therap. 2018; 41: 848–860. https://doi.org/10.1111/jvp.12688.