Drug Details

  • Drug Name: Penicillin
  • Common Name: Penicillin G®
  • Drug Type: Beta-lactam Antibiotic
  • Used For: treatment and prevention of bacterial infections
  • Species: Dogs, Cats
  • Administered: Capsules, Injectable, Oral liquid
  • How Dispensed: Prescription only
  • FDA Approved: Yes


General Description


Penicillin was the first antibiotic made available to humans during World War II. It was very effective against gram-positive bacteria, but didn’t last long and was susceptible to stomach acid so was wasted inside the body. It is often administered as a pre-operative injection, but is also used to treat dental and skin abcesses.


Bacteria often build resistance to this drug. Penicillin contain a molecular component known as a beta-lactam ring that is able to be interfered with by bacteria. This is how bacteria such as Staphylococci has been able to become resistant to these drugs.

This drug works best if given 1 hour before feeding or 2 hours after. It may be given with food is stomach upset occurs.


Penicillin is inactivated by gastric acid and therefore is more effective if given as an injection. Injectable form should be injected into the muscle - not subcutaneously and not into a blood vessel. Do not give more than 10 ml of Penicillin in one injection site.


How It Works


Penicillin kills bacteria by preventing them from building a proper cell wall while they grow. It accomplishes this by inhibiting the linking of peptidoglycan chains that are a major component in both gram-positive and some gram-negative bacteria’s cell walls.


Storage Information


  • Store tablets in a tightly sealed container at room temperature.
  • Keep oral liquid refrigerated- effective 14 days after mixed.
  • Injection is effective 24 hrs after reconstitution at room temperature and 7 days after reconstitution if refrigerated.


Missed Dose?


Give the dose as soon as possible. If it is almost time for the next dose, skip the missed dose, and continue with the regular schedule. Do not give your pet two doses at once.


Side Effects and Drug Reactions


Penicillin may result in these side effects:

  • Allergic reaction (Shock, labored breathing, etc)
  • Loss of appetite
  • Rash
  • Fever
  • Joint pain
  • Vomiting/Nausea
  • Diarrhea


Penicillin may react with these drugs:

  • Cephalosporin
  • Aminoglycosides
  • Bacteriostatics (Drugs that inhibit bacterial growth)




Penicillin is safe for use in dogs, cats, ferrets, hedgehogs, and some species of birds. USE CAUTION WHEN ADMINISTERING THIS DRUG TO OTHER SPECIES. Snakes, guinea pigs, some birds, and Chinchillas may be sensitive to this drug.