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.
Sourced from published veterinary references. Awaiting credentialed clinical reviewer — our editorial process.
Amoxicillin is dosed at 10–22 mg/kg PO q12-24h in bearded dragons, per Divers SJ. Empirical doses of antimicrobial drugs commonly used in reptiles. Exot DVM. 1998;1:23.; Hedley J. BSAVA Small Animal Formulary: Exotic Pets, British Small Animal Veterinary Association, Quedgeley, UK; 2020. — Verified against Carpenter's Exotic Animal Formulary, 6th Ed, p.212 (2026-08-01).. Verify against current literature before clinical use.
Each ExoticRx dose rule is graded by the strength of its primary evidence — see the editorial process.
Backed by 12 published sources
· Coles BH. Prescribing for exotic birds. In: Bishop Y, eds. The Veterinary Formulary, 5th ed., Pharmaceutical Press, London, UK; 2001:99-105.; Rupley AE. Critical care of pet birds. Vet Clin North Am Exot Anim Pract. 1998;1:11- 41. doi:10.1016/j.cvex.2016.01.014 — Verified against Carpenter's Exotic Animal Formulary, 6th Ed, p.405 (2026-08-01).
· Divers SJ. Empirical doses of antimicrobial drugs commonly used in reptiles. Exot DVM. 1998;1:23.; Hedley J. BSAVA Small Animal Formulary: Exotic Pets, British Small Animal Veterinary Association, Quedgeley, UK; 2020. — Verified against Carpenter's Exotic Animal Formulary, 6th Ed, p.212 (2026-08-01).
· FARAD Withdrawal Guidelines
· Hillyer EV, Brown SA. Ferrets. In: Birchard SJ, Sherding RG, eds. Saunders Manual of Small Animal Practice; WB Saunders, Philadelphia, PA; 1994:1317-1344. — Verified against Carpenter's Exotic Animal Formulary, 6th Ed, p.931 (2026-08-01).
· ISCAID UTI Guidelines; Plumb's 9th Ed
· Leib MS. Helicobacter Gastritis: Does it Cause Vomiting in Dogs and Cats? In: Western States Veterinary Conference Proceedings; 2012. — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.96 (2026-08-01).
Sample dosing (2 of 20 cited rules)
A dog/cat sample is shown here. Cited dosing for all 10 species — reptiles, birds, pocket pets, livestock, and equine — is free on the per-species pages above. Pro adds the weight-based calculator for every species.
Weese JS, Blondeau J, Boothe D, et al. International Society for Companion Animal Infectious Diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats. Vet J. 2019;247:8-25. Distributed by John Wiley & Sons, Inc. doi:10.1016/j.tvjl.2019.02.008 — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.96 (2026-08-01).
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· Morrisey JK, Carpenter JW, et al. Formulary. In: Quesenberry KE, OrcuttCJ, Mans C, et al. Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery, 4th ed., Elsevier, St. Louis, MO; 2021:620-630. — Verified against Carpenter's Exotic Animal Formulary, 6th Ed, p.703 (2026-08-01).
· Plumb's Veterinary Drug Handbook, 9th Ed
· Plumb's Veterinary Drug Handbook, 9th Ed, p.96, DOGS — 'Systemic infections (extra-label): 11 - 22 mg/kg PO every 8 hours'
· Verified against Papich/Saunders Handbook of Veterinary Drugs, 4th Ed, p.67 (2026-08-01).
· Visser C, Wijnbergen A, Bleich A. Maeuse und ratten. In: Fehr M, Sassenburg L, Zwart P, eds. Krankheiten der Heimtiere, Schluetersche Verlagsgesellschaft, Hannover, Germany; 2015. — Verified against Carpenter's Exotic Animal Formulary, 6th Ed, p.770 (2026-08-01).
· Weese JS, Blondeau J, Boothe D, et al. International Society for Companion Animal Infectious Diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats. Vet J. 2019;247:8-25. Distributed by John Wiley & Sons, Inc. doi:10.1016/j.tvjl.2019.02.008 — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.96 (2026-08-01).