Selected Antimicrobial Information – Farm Animal

Ampicillin [Farm Animal]

Restriction Status



Species Usage Dose
Camelids For Listeriosis 10-20mg/kg SQ, IV, or IM q12h, can dose up to q8h for listeriosis (extra-label)
Cattle Label dose 4.4-11mg/kg IM q24h, for up to 7d
For respiratory infections 22mg/kg SQ q12h (extra-label)
Small Ruminants For Listeriosis 10-20mg/kg IV or IM q12h (extra-label)
Swine Label dose 22mg/kg SQ q12h

Brand Name(s)



Ampicillin is a bactericidal, time-dependent β-lactam antibiotic with improved activity against Gram-negative organisms when compared to penicillin, though with somewhat less activity against Gram-positive organisms. Culture/susceptibility are recommended since resistance is widespread amongst Staphylococcus spp and many other pathogens. Ampicillin distributes widely through the plasma, and can cross the blood brain barrier when meninges are inflamed. It does not penetrate abscesses or sites of tissue necrosis well. Excretion is primarily in the urine.

Current Uses within OSU-VMC

  • Treatment of bovine respiratory disease associated with Aerobacter spp., Klebsiella spp., Pasteurella multocida, or Escherichia coli.
  • Treatment of swine respiratory infections associated with Pasteurella spp.
  • Treatment of swine colibacillosis (Escherichia coli enteritis).
  • Treatment of Listeriosis in camelids and small ruminants.

Contraindicated Uses

  • Inactivated in the presence of purulent or necrotic material (e.g. abscesses).

Illegal Uses

  • None

Formulations Available within the OSU Pharmacy

  • Ampicillin 1g/vial injectable suspension
  • Ampicillin 500mg/vial injectable suspension
  • Ampicillin NA 1g/vial injectable suspension
  • Ampicillin NA 500mg/vial injectable suspension


  • Culture and susceptibility recommended prior to treatment of suspected staphylococcal infections due to widespread resistance.
  • Ampicillin trihydrate (Polyflex®) should not be given IV due to risk of anaphylaxis and sudden death. Ampicillin sodium is safe for IV injection.


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OSU VMC Antimicrobial Use Guidelines Copyright © 2018 by The Ohio State University College of Veterinary Medicine is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.