Penicillin G (Pen-G) Injectable for Rabbits: Uses & Dosage

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Penicillin G is a prescription beta-lactam antibiotic that some rabbit-savvy veterinarians use by injection only in carefully selected cases. In rabbits, the route matters a great deal. Oral penicillin should not be given, because penicillins taken by mouth can disrupt normal gut bacteria and trigger severe, sometimes fatal, intestinal disease.

Your vet may choose an injectable form such as procaine penicillin G or a benzathine/procaine combination when the suspected bacteria are likely to respond and the benefits outweigh the risks. In rabbits, this medication is typically used extra-label, which means it is prescribed under veterinary judgment rather than from a rabbit-specific FDA label.

Because rabbits have a delicate gastrointestinal microbiome, Pen-G is not a medication to start, stop, or adjust at home without guidance. Your vet will decide whether it fits the infection type, your rabbit's age, hydration status, appetite, and any other medicines already being used.

Injectable Penicillin G is most often discussed in rabbits for treponematosis (rabbit syphilis/vent disease), where repeated injections are a well-known treatment option. Rabbit-savvy veterinarians may also use it for some susceptible bacterial skin, soft tissue, jaw, or dental abscess infections, often alongside wound care or surgery rather than as a stand-alone fix.

That said, not every rabbit infection is a good match for Pen-G. Many abscesses in rabbits are thick, walled-off, and difficult for antibiotics to penetrate. In those cases, your vet may recommend a combination of culture and sensitivity testing, flushing, debridement, tooth extraction, marsupialization, or long-term management depending on the location and your rabbit's overall health.

Pen-G does not treat viral disease, parasites, or every cause of nasal discharge, diarrhea, or skin sores. The best use depends on the likely bacteria involved, whether the infection is superficial or deep, and whether your rabbit can safely tolerate injections and monitoring.

Only your vet should determine the dose. In rabbits, published formularies and exotic-animal references describe different injectable Penicillin G protocols depending on the formulation and the condition being treated. Examples reported in veterinary references include procaine penicillin G around 40,000 IU/kg IM every 24 hours for 5-7 days for some situations, benzathine penicillin G around 42,000-60,000 IU/kg IM every 48 hours, and benzathine penicillin G 42,000-84,000 IU/kg SC every 7 days for 3 treatments for treponematosis protocols. These are reference examples, not home-dosing instructions.

The exact amount drawn into a syringe depends on your rabbit's body weight, the units per mL in the vial, the salt formulation used, and the route your vet chooses. Rabbits are small, so even a tiny measuring error can matter. Your vet may also adjust the plan based on kidney function, hydration, appetite, pain level, and whether the infection is responding.

If your rabbit misses a dose, do not double the next one unless your vet specifically tells you to. Ask for a written dosing sheet, injection demonstration, and recheck plan. If you are giving injections at home, contact your vet right away if you notice worsening appetite, diarrhea, marked pain at the injection site, or any sign that your rabbit is becoming weak or less responsive.

Possible side effects include pain or irritation at the injection site, reduced appetite, soft stool, diarrhea, lethargy, or stress from handling. Rabbits can decline quickly when they stop eating, so even a mild drop in appetite deserves prompt attention. Call your vet the same day if your rabbit is eating less, producing fewer droppings, or seems uncomfortable after an injection.

More serious reactions can include severe gastrointestinal upset, dehydration, collapse, breathing changes, facial swelling, hives, or anaphylaxis. While the biggest gut risk is associated with oral penicillins, any rabbit on antibiotics should be monitored closely for digestive changes. If your rabbit develops diarrhea, profound lethargy, trouble breathing, or stops eating, see your vet immediately.

Longer courses may also bring practical issues such as repeated injection-site soreness, stress with restraint, or incomplete response if the infection is deep or encapsulated. That is one reason your vet may pair medication with dental treatment, abscess surgery, culture testing, pain control, or assisted feeding support.

Penicillin G can interact with other medications, so your vet should review everything your rabbit receives, including prescription drugs, compounded medications, supplements, probiotics, and topical products. As a general rule, antibiotics that are bacteriostatic rather than bactericidal may reduce how well penicillins work in some situations, and combinations with other drugs may change monitoring needs.

References for penicillins in companion animals also note caution with drugs such as aminoglycosides because both the infection itself and supportive-care needs can complicate kidney monitoring. Rabbits being treated for serious infections may also be on pain medication, gut-motility support, fluids, or other antibiotics, so the full plan matters more than any one drug in isolation.

Tell your vet if your rabbit has ever had a reaction to a penicillin, cephalosporin, or injectable medication. Also mention any history of kidney disease, dehydration, reduced appetite, or previous antibiotic-associated diarrhea, since those details can change whether Pen-G is a reasonable option.