Penicillin G for Cats

Cat · Felis catus · typical adult weight 2.50–7.00 kg

Penicillin G is dosed at 13.2–26.4 mg/kg IM q12-24h in cats, per Plumb's Veterinary Drug Handbook, 9th Ed. Penicillin G is used in cats for Gram-positive infections. Routes documented in cats: IM. A typical adult cat weighs 2.50–7.00 kg. ExoticRx lists 1 cited dose rule for Penicillin G in cats, drawn from published veterinary references. Verify against current literature before clinical use.

US trade names: Pen-G, Crysticillin

Contraindicated in Rabbit, Guinea Pig, Chinchilla, Hamster, Degu

Rabbit: Oral beta-lactams cause fatal dysbiosis in rabbitsOral amoxicillin (and other oral beta-lactams) selectively destroy gram-positive hindgut flora in rabbits, allowing Clostridium spiroforme overgrowth and fatal enterotoxemia. Never administer oral beta-lactams to rabbits. Parenteral administration carries a lower risk than the oral route, but is not established as safe in rabbits.
Guinea Pig: Oral beta-lactams cause fatal dysbiosis in guinea pigsOral amoxicillin reliably causes Clostridium difficile-mediated fatal enterotoxemia in guinea pigs. Same mechanism as in rabbits. Parenteral administration carries a lower risk than the oral route; parenteral ceftiofur specifically has been given to guinea pigs and chinchillas without adverse effect.
Chinchilla: Oral beta-lactams cause fatal dysbiosis in chinchillasChinchillas are hindgut fermenters with the same flora dependence as rabbits and guinea pigs. Oral penicillins and oral cephalosporins trigger Clostridium overgrowth and fatal enterotoxemia. Never give oral beta-lactams; parenteral routes and trimethoprim-sulfa, fluoroquinolones, or chloramphenicol are the safer choices.
Hamster: Oral beta-lactams cause fatal enterocolitis in hamstersHamsters are exquisitely susceptible to antibiotic-associated Clostridium difficile enterocolitis — the hamster is the classic laboratory model for it. Oral penicillins and cephalosporins are reliably fatal. Never administer oral beta-lactams.
Degu: Oral beta-lactams risk fatal dysbiosis in degusDegus are caviomorph hindgut fermenters closely related to chinchillas and guinea pigs. Degu-specific data is limited, so this warning is extrapolated from those related hystricomorphs — but the shared physiology makes oral beta-lactam enterotoxemia the expected outcome. Treat as contraindicated; use the safer alternatives.

Dose ranges

Route	Dose	Frequency	Duration	Indication	Evidence	Source
IM	13.2–26.4 mg/kg	q12-24h	7-14 days	Gram-positive infections	Strong	Plumb's Veterinary Drug Handbook, 9th Ed

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Mechanism of action

Inhibits bacterial cell wall synthesis by binding PBPs. Bactericidal. Narrow spectrum: primarily gram-positive and some anaerobes.

Side effects & warnings

CONTRAINDICATED in rabbits, guinea pigs, hamsters. Hypersensitivity reactions. Procaine form: IM/SC only (never IV). Potassium form: slow IV only. Pain at injection site.

Species-specific contraindications and adverse-reaction reports for cats may differ from canine / feline reference data — consult the primary citations listed with each rule.

Frequently asked questions

What is the dose of Penicillin G for Cats?

Penicillin G dose range in cats, with cited source references: IM 13.2–26.4 mg/kg q12-24h. Reference ranges from cited sources — verify against current literature before clinical use.

How is Penicillin G administered in Cats?

Documented routes for Penicillin G in cats: IM.

How long is Penicillin G given in Cats?

Cited course lengths for Penicillin G in cats include: 7-14 days. Duration depends on the indication — match it to the specific dose rule in the table above.

What conditions does Penicillin G treat in Cats?

Penicillin G is indicated in cats for: Gram-positive infections.

What are the side effects of Penicillin G in Cats?

These are general warnings for Penicillin G across species; consult the cat dosing table above for species-specific guidance. CONTRAINDICATED in rabbits, guinea pigs, hamsters. Hypersensitivity reactions. Procaine form: IM/SC only (never IV). Potassium form: slow IV only. Pain at injection site.

Other Antibiotic drugs with cat dosing

Amikacin Amoxicillin Amoxicillin Injectable Amoxicillin-Clavulanate Ampicillin Azithromycin Aztreonam Bacitracin Carbenicillin Cefaclor Cefadroxil Cefazolin

Penicillin G dosing in other species

Dogs Goats Sheep

See all species for Penicillin G See all drugs for Cats

Why a species-specific page? Penicillin G pharmacokinetics differ across species: dose ranges, intervals, and route preferences are not interchangeable. Cross-extrapolation from canine doses is unsafe in cats — the rules above are the citations specific to this species, not generic recommendations.

Sourced from published veterinary references; awaiting credentialed clinical reviewer. See our editorial process. Reference only — not veterinary advice.