Penicillin G (potassium/sodium/procaine/benzathine)

What is this medication for?

• Gram-positive aerobes/anaerobes; tetanus, botulism, strangles, foal C. difficile; general susceptible infections
• Susceptible infections (procaine/combo products, label with withdrawals)
• Susceptible gram-positive/anaerobic/spirochete infections (into a vein route for serious)

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

• Formulation = prescription: aqueous for sepsis-level peaks, procaine for practical every 12 hours coverage, benzathine ONLY when low-level-days-long suffices (it never achieves MIC against moderately sensitive bugs).

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• Hypersensitivity (Class risk)
• into a muscle injection pain (procaine) (Route effect)

Worth a phone call to your veterinarian

• Any new symptom that worries you.

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• CNS effects at very high doses (seizures) (Overdose)
• Procaine reactions: excitement, wobbliness/unsteadiness, collapse (idiosyncratic) (Formulation-specific)

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Penicillin hypersensitivity (unless no alternative)
• has or has had: K-salt into a vein rate in renal/heart failure (potassium load); food-animal withdrawal per product label

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Aminoglycosides
  • Bacteriostatics (tetracycline/chloramphenicol class)
  • Probenecid

Storage and handling

Aqueous: refrigerate, use promptly after reconstitution; never mix aminoglycosides in same vial/line (inactivation).

Good to know

• The strangles rule is pure clinical judgment: fever-only early = treat; breathing-well lymphadenopathy = don't (abscess maturation is immunology's job); depressed/dyspneic = treat hard.
• Formulation = prescription: aqueous for sepsis-level peaks, procaine for practical every 12 hours coverage, benzathine ONLY when low-level-days-long suffices (it never achieves MIC against moderately sensitive bugs).
• The procaine-reaction story (snorting, circling horse after injection) is the classic barn-call trivia — distinguish from anaphylaxis.
• The "if still susceptible, prefer the natural penicillin" principle: narrows spectrum, preserves the newer drugs.