Penicillin for Dogs and Cats: Uses and Side Effects

Penicillin is an antibiotic used to treat certain susceptible bacterial infections in dogs and cats.

Different forms of penicillin are available, including injectable Penicillin G and oral Penicillin V, although the oral form is rarely used in veterinary medicine.

Your veterinarian will determine whether penicillin is appropriate for your pet based on the type of infection and the formulation needed.

What Is Penicillin Used for in Dogs and Cats?

Penicillin is an antibiotic used to treat susceptible bacterial infections in dogs and cats, as well as cattle, horses, and swine.

Penicillin G Procaine: This injectable form is FDA-approved for use in horses, cattle, sheep, dogs, and cats for respiratory tract infections and in swine for skin infections.

Penicillin G injection: This form is sometimes used in dogs for certain bacterial infections, including leptospirosis.

Penicillin V: This oral form is rarely used in veterinary medicine because it must be given several times a day on an empty stomach.

FDA approval and extra-label use: Penicillin V and Penicillin V Potassium are FDA-approved for human use as generic Penicillin V tablets or as a powder mixed with water to create an oral liquid.

Penicillin V is not FDA-approved as a veterinary medication. However, veterinarians may legally prescribe certain human medications to animals in specific circumstances. This is called extra-label or off-label use because the use is not described on the medication label.

Your veterinarian will determine whether penicillin is appropriate for your pet.

How Does Penicillin Work in Dogs and Cats?

Penicillin works by preventing susceptible bacteria from creating a necessary part of their cell walls.

Without this part of the cell wall, the bacteria become weakened and are destroyed, causing them to die.

How To Give Penicillin to Dogs and Cats

Give penicillin exactly as directed by your veterinarian. Penicillin V is best given without food.

Administration instructions:

• Follow the directions on the medication label or those provided by your veterinarian.
• If your pet develops stomach upset when taking Penicillin V, giving it with a small amount of food may help.

Penicillin V oral suspension: The liquid form is usually supplied as a powder that must be mixed with water.

• Follow the mixing directions closely and use the exact amount of water specified to create the suspension.
• Shake the suspension well.
• Storing mixed penicillin in the refrigerator is preferred.
• Discard any unused suspension after 14 days.
• Always confirm storage requirements by reading the prescription label.

Missed a Dose?

If you miss a dose of penicillin, speak with your veterinarian about what to do. Generally, they may instruct you to give it when you remember. If it is almost time for your pet's next dose, they may recommend skipping the missed dose and resuming the normal dosing schedule.

Do not give extra or double doses.

Penicillin Side Effects in Dogs and Cats

Penicillin can cause gastrointestinal side effects in dogs and cats, although allergic reactions can also occur.

Gastrointestinal side effects may include:

• Vomiting
• Diarrhea
• Loss of appetite

Allergic reactions: Penicillin allergies in animals are rare but can happen. Signs may include:

• Skin rashes
• Fever
• Collapse
• Difficulty breathing

Important species warning: Penicillin V, the oral form, should not be used in horses, rabbits, guinea pigs, gerbils, hamsters, or chinchillas because life-threatening diarrhea can occur in these species.

Human Side Effects

Penicillin is also a prescription medication for humans, but human and veterinary doses and side effects may differ.

If you accidentally ingest a pet medication, call your physician or the National Poison Control Center hotline at 800-222-1222.

If you are allergic to penicillin, talk to your veterinarian about using another medication or always wear gloves when handling this medication.

When To Call Your Veterinarian

Call your veterinarian if:

• Your pet develops severe side effects.
• Your pet's condition worsens or does not improve with treatment.
• You see or suspect an overdose.
• You have additional questions or concerns about the use of penicillin.

Penicillin Overdose in Dogs and Cats

An overdose of penicillin is unlikely to cause toxicity, but side effects can occur.

Possible effects include:

• Vomiting
• Diarrhea
• Decreased appetite

Large overdoses or prolonged use may cause:

• Lack of coordination
• Seizures
• Breathing problems
• Fluid retention
• Rapid heart rate

Allergic reactions: Penicillin allergies in pets are rare but can happen. Signs may include:

• Skin reactions
• Watery eyes
• Hives (urticaria)
• Facial swelling
• Vomiting
• Diarrhea
• Anaphylaxis

If you suspect your pet has received an overdose, immediately contact your veterinarian, seek emergency veterinary care, or contact an animal poison control center. Consultation fees may apply.

• Pet Poison Helpline: (855) 764-7661
• ASPCA Animal Poison Control: (888) 426-4435

How To Store Penicillin

Store penicillin tablets and powders at controlled room temperatures between 68–77 F (20–25 C).

Storage instructions:

• Store reconstituted penicillin suspension in the refrigerator.
• Discard any unused reconstituted suspension after 14 days.
• Keep the container tightly closed to protect the medication from moisture and light.
• Always confirm storage requirements by reading the medication label.