What is Penicillin G used for?

Penicillin G is indicated for: Bacterial infection (general), Bacterial infections, Gram-positive bacterial infection, listeriosis, Treponema cuniculi-induced blepharitis (rabbit syphilis).

Which species have cited Penicillin G dosing data?

Penicillin G dosing in the ExoticRx formulary covers 5 species: Ferret, Goat (Caprine), Pet Rat, Rabbit (Domestic), Sugar Glider.

Is Penicillin G a controlled substance?

Penicillin G is not federally scheduled in the US. Controlled-drug status differs by country — verify your local rules.

What are the warnings or contraindications for Penicillin G?

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

What are the side effects of Penicillin G?

Reported side effects, adverse reactions, and contraindications for Penicillin G: CONTRAINDICATED in rabbits, guinea pigs, hamsters. Hypersensitivity reactions. Procaine form: IM/SC only (never IV). Potassium form: slow IV only. Pain at injection site.

How does Penicillin G work?

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

Penicillin G

US brand names:Pen-G, Crysticillin

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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.

Penicillin G is dosed at 40000 IU/kg SC, IM q24h in ferrets, per Besch-Williford CL. Biology and medicine of the ferret. Vet Clin North Am Small Anim Pract. 1987;17:1155-1183. — Source: Carpenter's Exotic Animal Formulary, 6th Ed, p.933 — Carpenter's Exotic Animal Formulary 6th ed, Table 11.1 (Antimicrobial Agents Used in Ferrets). The copy held is an ebook conversion with no printed page numbers, so the table — not the page — is the citable location. — SOURCE EDITION: Carpenter's Exotic Animal Formulary — ISBN 9780323833929, https://openlibrary.org/isbn/9780323833929. Verify against current literature before clinical use.

Backed by 5 published sources

· Besch-Williford CL. Biology and medicine of the ferret. Vet Clin North Am Small Anim Pract. 1987;17:1155-1183. — Source: Carpenter's Exotic Animal Formulary, 6th Ed, p.933 — Carpenter's Exotic Animal Formulary 6th ed, Table 11.1 (Antimicrobial Agents Used in Ferrets). The copy held is an ebook conversion with no printed page numbers, so the table — not the page — is the citable location. — SOURCE EDITION: Carpenter's Exotic Animal Formulary — ISBN 9780323833929, https://openlibrary.org/isbn/9780323833929
· FARAD Withdrawal Guidelines [2026-08-05: FARAD (Food Animal Residue Avoidance Databank, https://www.farad.org/) publishes meat/milk WITHDRAWAL intervals for extralabel use — it is not a dosing authority. This dose could not be corroborated in Plumb's 10th ed (held) for this species, unlike the other 15 FARAD-cited rules. Needs a product label or primary reference before it can be considered sourced.] — SOURCE EDITION: Plumb's Veterinary Drug Handbook — ISBN 9781394172207, https://openlibrary.org/isbn/9781394172207

GelattKN. Exotic animal ophthalmology. In: GelattKN, eds. Essentials of Veterinary Ophthalmology; Blackwell, Oxford, UK; 2005:413-438. — Source: Carpenter's Exotic Animal Formulary, 6th Ed, p.874 — Carpenter's Exotic Animal Formulary 6th ed, Table 10.9 (Ophthalmologic Agents Used in Rabbits). The copy held is an ebook conversion with no printed page numbers, so the table — not the page — is the citable location. — SOURCE EDITION: Carpenter's Exotic Animal Formulary — ISBN 9780323833929, https://openlibrary.org/isbn/9780323833929; Veterinary Ophthalmology — ISBN 9781119441830, https://openlibrary.org/isbn/9781119441830

· Morrisey JK, Carpenter JW, et al. Formulary. In: Quesenberry KE, Orcutt CJ, Mans C, et al. Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery, 4th ed., Elsevier, St. Louis, MO; 2021:620-630. | Ness RD, Johnson-Delaney C. Sugar gliders. In: Quesenberry KE, Carpenter JW, eds. Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery, 3rd ed., Saunders/Elsevier, St. Louis, MO; 2012:393-410. — Source: Carpenter's Exotic Animal Formulary, 6th Ed, p.704 — SOURCE EDITION: Carpenter's Exotic Animal Formulary — ISBN 9780323833929, https://openlibrary.org/isbn/9780323833929; Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery — ISBN 9780323484350, https://openlibrary.org/isbn/9780323484350

· Morrisey JK, Carpenter JW. Formulary. In: Quesenberry KE, Carpenter JW, eds. Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery, 4th ed., Elsevier, St. Louis, MO; 2021:620-630. — Source: Carpenter's Exotic Animal Formulary, 6th Ed, p.773 — SOURCE EDITION: Carpenter's Exotic Animal Formulary — ISBN 9780323833929, https://openlibrary.org/isbn/9780323833929; Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery — ISBN 9780323484350, https://openlibrary.org/isbn/9780323484350 [w3r2 2026-08-14] LOCATOR: Carpenter 6th ed, Table 9.1 (Antimicrobial and Antifungal Agents Used in Rodents), Penicillin G (procaine) row bearing superscript 130. Held copy is a paginationless ebook conversion, so the table and not the page is the citable location.

Penicillin G

Drug Class

Routes

Indications

Mechanism of Action

Side effects & warnings

Species with Penicillin G dosing data (5 dose rules)

Evidence levels across 5 dose rules

Backed by 5 published sources

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Penicillin G

Drug Class

Routes

Indications

Mechanism of Action

Side effects & warnings

Species with Penicillin G dosing data (5 dose rules)

Evidence levels across 5 dose rules

Backed by 5 published sources

Upgrade for Full Details

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