What is Carbenicillin used for?

Carbenicillin is indicated for: Urinary tract infections, Urinary tract infections (Pseudomonas).

Which species have cited Carbenicillin dosing data?

Carbenicillin dosing in the ExoticRx formulary covers 3 species: Cat (Domestic), Dog (Domestic), Russian Tortoise.

Is Carbenicillin a controlled substance?

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

What are the side effects of Carbenicillin?

Reported side effects, adverse reactions, and contraindications for Carbenicillin: High sodium content in parenteral form. May cause platelet dysfunction at high doses. GI upset with oral use.

Carbenicillin

US brand names:Geocillin, Pyopen

Calculate dosage

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.

Carbenicillin is dosed at 200–400 mg/kg IM q 24 h in russian tortoises, per Merck Veterinary Manual. Antimicrobial Drugs Used in Reptiles (dosing table). Rahway (NJ): Merck & Co.; accessed 2026. URL: https://www.merckvetmanual.com/multimedia/table/antimicrobial-drugs-used-in-reptiles. Verify against current literature before clinical use.

Drug Class

Antibiotic

Routes

POIVIM

Indications

Urinary tract infectionsUrinary tract infections (Pseudomonas)

Mechanism of Action

Inhibits bacterial cell wall synthesis by binding PBPs. Extended-spectrum penicillin with Pseudomonas activity.

Side effects & warnings

High sodium content in parenteral form. May cause platelet dysfunction at high doses. GI upset with oral use.

Species with Carbenicillin dosing data (3 dose rules)

Cat (Domestic)Dog (Domestic)Russian Tortoise

Species references:All Cat (Domestic) drugs All Dog (Domestic) drugs All Russian Tortoise drugs

Evidence levels across 3 dose rules

Moderate×1Weak×2

Each ExoticRx dose rule is graded by the strength of its primary evidence — see the editorial process.

Backed by 3 published sources

· Merck Veterinary Manual. Antimicrobial Drugs Used in Reptiles (dosing table). Rahway (NJ): Merck & Co.; accessed 2026. URL: https://www.merckvetmanual.com/multimedia/table/antimicrobial-drugs-used-in-reptiles
· Papich MG. Saunders Handbook of Veterinary Drugs, 4th ed (2016), Carbenicillin, p.135, 'Small Animal Dosage — Dogs and Cats'
· Papich, Saunders Handbook of Veterinary Drugs (Small and Large Animal), p.135, Carbenicillin — Small Animal Dosage, Dogs and Cats, carbenicillin indanyl sodium oral row

Sample dosing (2 of 3 cited rules)

A dog/cat sample is shown here. Cited dosing for all 3 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.

Species	Route	Dose	Frequency	Evidence	Source
Dog (Domestic)	PO	10 mg/kg	q8h	Moderate	Papich, Saunders Handbook of Veterinary Drugs (Small and Large Animal), p.135, Carbenicillin — Small Animal Dosage, Dogs and Cats, carbenicillin indanyl sodium oral row
Cat (Domestic)	PO	10 mg/kg	q8h	Weak	Papich MG. Saunders Handbook of Veterinary Drugs, 4th ed (2016), Carbenicillin, p.135, 'Small Animal Dosage — Dogs and Cats'

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