Penicillin G

What is penicillin G?

Penicillin G (brand names VetriPen G, PenOne Pro™, others) is an antibiotic used to treat susceptible infections in cats, dogs, chickens, horses, livestock, ferrets, hedgehogs, rabbits, and other animals.

It is used off label (extra label) in cats, dogs, and other companion animals. Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.

How do I give my pet penicillin G?

• Penicillin G comes in an injectable suspension form (pre-made or powder to reconstitute). 
• Injections may be given intramuscularly (into the muscle), subcutaneously (under the skin), or intravenously (into the vein). 
• Follow your veterinarian’s directions on how to give injections and proper disposal of sharps.
• Wear gloves while administering and wash your hands when done. 
• Avoid contact with eyes.
• Give this medication to your pet for the entire time prescribed by your veterinarian, even if it appears that your pet is feeling better.

This medication should start working within 1–2 hours, but its effects may not be noticeable for 1-2 days.

What if I miss giving my pet the medication?

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

Are there any potential side effects from penicillin G?

Penicillin G may cause the following side effects:

• stinging or mild pain at injection site
• diarrhea, vomiting, loss of appetite

The following reactions are rare, but if they occur, contact your veterinarian immediately:

• an allergic reaction such as irregular breathing, rash, fever, puffiness and swelling around the face

Drug sensitivities can develop over time with repeated exposure. Your pet may have no reaction after the first few doses, but may develop a sensitivity later. It is important to watch for signs of an allergic reaction over the entire course of treatment.

Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately. This short-acting medication should stop working within 24 hours, though effects may be prolonged in pets with kidney or liver disease.

Are there any risk factors for this medication?

This medication should NOT BE USED in:

• animals allergic to any of the components or allergic to other penicillin-like drugs 

This medication should be USED WITH CAUTION in:

• animals with electrolyte imbalances
• animals with heart conditions
• rabbits and other animals sensitive to penicillin-like drugs, as ingestion may cause severe reactions
• snakes
• birds
• turtles

Are there any drug interactions I should be aware of?

Certain medications should be USED WITH CAUTION when given with penicillin G, including but not limited to:

• aminoglycosides or cephalosporins
• chloramphenicol, erythromycin, tetracyclines
• methotrexate

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment.

Is any monitoring needed with this medication?

• Your veterinarian may schedule a follow-up visit after the course of medication is complete to ensure the condition has been cleared and/or do additional testing to ensure this is the right medication for the condition present. In this case, follow your veterinarian’s directions.
• At home, monitor for any abnormal changes. If these occur, discontinue the medication, and contact your veterinarian.

How do I store penicillin?

• Store prepared solutions in a place protected from light and heat, at 2°C-8°C (36°F-46°F).
• Powders may be kept at room temperature until reconstituted.
• If your veterinarian or pharmacist has made a special (compounded) formulation for your pet, follow the storage recommendations and expiration date for the product.
• Keep medication out of reach of children and pets.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility. Adverse effects should also be reported to the FDA or Health Canada.