Selected Antimicrobial Information – Equine

Penicillin [Equine]

Restriction Status



Species Usage Dose
For susceptible infections (Sodium penicillin G, potassium penicillin G) 22,000-44,000 IU/kg IV q6h, given slowly
For susceptible infections (Procaine penicillin G) 22,000 IU/kg IM q12h

Brand Name(s)

sodium penicillin G, potassium penicillin G, procaine penicillin G; penicillin V potassium


Penicillin G is a bactericidal, time-dependent β-lactam antibiotic with good activity against many Gram-positive organisms, though it is not effective against β-lactamase-producing Staphylococcus spp., α-Streptococcus spp., or Rhodococcus equi. It has limited efficacy against Gram-negative bacteria. Penicillin G distributes widely through the plasma but has low lipid solubility and does not penetrate abscesses or sites of tissue necrosis well. The active form of penicillin G is excreted in high concentration in the urine.

Acceptable Uses

  • First line choice for treatment of streptococcal infections such as Streptococcus equi (strangles), or Streptococcus zooepidemicus (upper and lower respiratory infection).
  • Treatment of clostridial infections such as clostridial myositis, botulism, or tetanus.
  • Treatment of susceptible urinary tract infections.
  • When used in combination with gentamicin, a first line choice for broad-spectrum therapy (as in cases of peritonitis, pleuropneumonia, cholangiohepatitis, sepsis, or endocarditis).
  • Treatment of orthopedic infections (osteomyelitis, septic arthritis) when β-lactamase-producing Staphylococcus spp. or Enterobacteriaceae have been ruled out by culture.

Unacceptable Uses

  • Treatment of suspected or cultured-confirmed Enterobacteriaceae infections.
  • 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

  • Penicillin gel 5ml/syringe
  • Penicillin gel 10ml/syringe
  • Penicillin G Potassium 20mmu injectable suspension
  • Penicillin G Procaine injectable suspension (1 ml, 30 ml, 100 ml, 250 ml)


  • Intravascular injection of procaine penicillin G can cause excitement, seizure-like activity, and death. Procaine penicillin G should be given IM only.
  • Rapid IV administration of potassium penicillin can cause head shaking/lip smacking, salivation, lacrimation, increased borborygmi, colic, agitation, and soft to liquid feces. Potassium penicillin should be given over 5 minutes.


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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.