Food Animal Drug Regulations

FA Drug Regulation Summary

Food animal drugs are tricky

    • Pot bellied pigs have to follow pig (major species) rules
    • Camelids, sheep and goats are under MUMs rules and have more flexibility but are still food animals
    • Use FARAD and VetGram to identify prohibited drugs, ELDU allowances and withholding times
      • This can be very tricky for goats etc. – try to find a cattle version
      • You can contact FARAD and ask
    • Oral drugs in ruminants often don’t work. Meloxicam does
      • Use of meloxicam is a bit edgy. We justify it as a better analgesic and there are no FDA approved analgesics in food animals yet

To determine withholding

  • Typically count on 5 half-lives to clear a drug
  • If you double the drug amount, add 1 half life
  • Elimination is via the same process regardless of route of administration
    • if you can figure out the difference in peak values, that can help with half life calculations
      • Iv administration ->  high, fast peaks
      • IM administration -> slower peaks but generally same peak level
        • will take a bit longer to eliminate
      • PO administration – slower peaks and lower peaks
        • usually take less time to eliminate since not as much drug available

Half-life review

  • One half-life = 50% drug cleared
  • Two half-lives = 50 + 25 = 75% drug cleared
  • Three half-lives=75 + 12.5 = 87.5% drug cleared
  • Four half-lives=87.5 + 6.25 = 93.75% drug cleared
  • Five half-lives=93.75 + 3.125 = 96.875% drug cleared

General rule of thumb= After *5* half-lives, the majority of the drug has been cleared from the body

For example:

  1. Drug X t ½ is 7 hours, so  5 x 7 hours=35 hours before 97% of drug is cleared from body
  2. Drug Y t ½ is 2-3 hours, so  5 x 2-3 hours = 10-15 hours before 97% of drug is cleared from body
  3. After giving 3600mg Drug Z IV to a horse, how much of drug is left in the body, after 4 hours?

t ½  = ~2 hours (if given IV)

4 hours is 2 half-lives (4 hours/2 hours (t ½ )

So, after two half-lives, 75% of drug has been cleared, so 3600mg x 75% clears 2700mg from the body

But, we want to know how much is remaining in the body, so 100-75% = 25% of drug is remaining, so our answer is:

3600mg (dose given) x 25% = 900mg remaining in body

 

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Large Animal Surgery - Supplemental Notes Copyright © by Erin Malone, DVM, PhD is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.