Abstract: Update on withdrawal intervals following extralabel use of procaine penicillin G in cattle and swine
Extralabel drug use (ELDU) is defined as the use of an FDA-approved medication in a manner that differs from what is provided on the label of the medication.1 Administration of the medication to a different species or at a different dose, volume, route, duration, indication, or frequency than indi-cated on the label is considered ELDU. Extralabel drug use also requires an extended withdrawal pe-riod to avoid violative residues, and practitioners can get advice on withdrawal intervals (WDIs) fol-lowing ELDU from the Food Animal Residue Avoid-ance and Depletion Program (FARAD). Penicillin is one of the most commonly used medications to treat disease in food-producing animals across the globe.1,2 However, it was approved over 40 years ago, and in the US, the current FDA-approved label dose (6,600 U/kg [3,000 U/kg]) is not consistent with current clinical practice. Globally, the dose of penicillin utilized has been changed in order to achieve the desired clinical effect. The Canadian label dose has been increased to 15,000 U/kg in swine and 21,000 U/kg in cattle. In the UK, the la-bel dose is 8,000 to 10,000 U/kg for both swine and cattle. When an antimicrobial susceptibility test is performed, the penicillin dose used by the Clinical and Laboratory Standards Institute (CLSI) to deter-mine susceptible breakpoints for bacterial patho-gens is 22,000 U/kg IM for cattle and 33,000 U/kg IM for pigs.3 According to FARAD submissions, as of January 2021, penicillin is 1 of the top 25 drugs for which WDIs are requested following ELDU. Those submissions were prompted by the use of an above-label dose to achieve clinical effect or administra-tion of a greater-than-recommended volume at an injection site or by an unlabeled route. Such devia-tions from the approved label alter the known meat and milk WDIs for both cattle and swine. Given that above-label doses of penicillin are required to achieve clinical efficacy, a new FARAD Digest regard-ing the development of new WDIs for penicillin fol-lowing ELDU was needed. The purpose of this digest is to describe how common ELDU of penicillin alters WDIs for both cattle and swine.
Halleran J, Papich M, Li M, Lin Z, Davis J, Maunsell F, Riviere J, Baynes R, Foster D. Update on withdrawal intervals following extralabel use of procaine penicillin G in cattle and swine. JAVMA. 2021 Nov. https://doi.org/10.2460/javma.21.05.0268