Swine Morsels

Swine Morsels VII

Trivia in pharmacology
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By Monte W. Fuhrman, - DVM, BSc
Published: Mar. 08, 2006

Fellow Sioux Nationers: I have picked up a few exciting tidbits for those of us who just don’t get out much and don’t receive very many Christmas cards. I’ll divide them amongst the next series of "Swine Morsels". Let’s start with some trivia in pharmacology.

  • Penicillin lasts a lot longer than we may think in pig meat/carcass, especially if used at a dose that is extra label. Penicillin, to be effective against pig diseases it is used to treat, almost has to be used at extra-label dosages. Efficacy of Beta-Lactams (of which penicillin is one) revolves around keeping enough of the drug in the serum over a period of time. If the serum level falls below the breakpoint, the bacteria can grow once again. Recent violative residues have occurred because of Erysipelas break in near-market age hogs. One instance of violative residue was because of Benzathine (long acting) penicillin being used. This formulation may stick around weeks in the pig. Dosages deemed necessary to effectively treat Erysipelas will also cause violative drug residues in pigs if prolonged extended withdrawal periods are not followed.
  • Dexamethasone causes severe immune function impairment in CATTLE. However, there is no, or little immune dysfunction described in the pig with the doses of Dexamethasone we use. Dexamethasone is well absorbed orally.
  • Recent studies in feedlot cattle with a non-steroidal anti-inflammatory drug showed increased numbers of repeat ‘pulls’ when that drug was used. Pediatric doctors in people are now reverting back to allowing one of the immune functions (fever) act as it should without being impaired by antipyretic drugs. Real treatment effects of liquid aspirin really need to be more fully evaluated and once again, veterinarians have to be the entity to decide if aspirin will be an appropriate treatment or not.
  • When you see an antibiotic sensitivity test, how much weight do we, as veterinarians, put on those results while we decide which antimicrobial treatments may be appropriate for a given disease process? Consider the following:
  • MIC (mean inhibitory concentration) really only indicates a breakpoint that pharmacologists have determined may correlate well with perceived clinical response to treatment with an antimicrobial against a specific RESPIRATORY disease.
  • These breakpoints are nearly exclusively extrapolated from human and rat antibiotic response information. We already know some drugs affect different species differently.
  • There is very little non-biased literature available for this type of breakpoint decision making data in domestic animals. Consider this example. We have an enteric bacterial disease in some nursery pigs. We have received an antibiotic sensitivity report using MIC’s on the bacterial disease causing agent. What does that sensitivity report tell us? NOT MUCH REALLY - - because the MIC’s for those drugs are based on respiratory disease response to treatments. Still - - right now - - this method is about the best tool we have to help us in our decision making. I just think we all have to know where MIC information comes from.
  • Here is a weird one: CTC when administered at 100 gm/ton in feed will show virtually the same serum antibiotic concentration as CTC when administered at 400 gm/ton. No kidding! However, when CTC is added at 1000 gm/ton, the serum levels double to triple over that of 400 or 100 gm/ton. With OTC, that is not the case. 400 gm/ton of OTC reaches virtually the same serum concentrations as 1100 gm/ton. Both concentrations are pretty low. That could be one of the reasons, I believe, that we see clinical response to CTC better than OTC for bacterial respiratory disease. (Monte’s opinion only) Stay tuned for more Swine Morsels