Selected Antimicrobial Information – Equine

Ampicillin [Equine]

Restriction Status



Species Usage Dose
For treatment of streptococcal lower airway infections or neonatal sepsis.
  • Adults: 15-40mg/kg IV q6h (extra-label use)
  • Foals: 20-40mg/kg IV q6 (extra-label use)

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. 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 urine.

Acceptable Uses

  • When used in combination with amikacin (an aminoglycoside), for treatment of neonatal sepsis.
  • For treatment of streptococcal lower airway infections.
  • Can be used as IV an alternative to penicillin in most cases.

Unacceptable Uses

  • Inactivated in the presence of purulent or necrotic material (e.g. abscesses).
  • Empirical treatment of suspected staphylococcal infections.
  • In combination with a bacteriostatic antimicrobial, efficacy is decreased.

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


  • 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.