Ampicillin for Cats

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

Ampicillin is dosed at 22–40 mg/kg IV q6-8h in cats, per Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.107 (2026-08-01). — Plumb's 10th ed (held) printed p.78, Ampicillin monograph spanning p.78-81; page located 2026-08-05 from the book's own running heads, verified to name the drug in its body text. — SOURCE EDITION: Plumb's Veterinary Drug Handbook — ISBN 9781394172207, https://openlibrary.org/isbn/9781394172207. Ampicillin is used in cats for Surgical prophylaxis, bacteremia. Routes documented in cats: IV. A typical adult cat weighs 2.50–7.00 kg. ExoticRx lists 1 cited dose rule for Ampicillin in cats, drawn from published veterinary references. Verify against current literature before clinical use.

US trade names: Polyflex

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
IV	22–40 mg/kg	q6-8h	Peri-operative or 7-14 days	Surgical prophylaxis, bacteremia	Strong	Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.107 (2026-08-01). — Plumb's 10th ed (held) printed p.78, Ampicillin monograph spanning p.78-81; page located 2026-08-05 from the book's own running heads, verified to name the drug in its body text. — SOURCE EDITION: Plumb's Veterinary Drug Handbook — ISBN 9781394172207, https://openlibrary.org/isbn/9781394172207

What each reference text prints

Every held source for this drug and species, as printed. Where they differ, both are shown — the choice is yours, not ours.

The sources disagree for this combination. The ranges below do not overlap on a comparable route. This is not an error in one of them — published veterinary references differ, and reconciling them for a particular patient is a clinical judgement.

Printed doses in mg/kg for this drug and species, by source
Dose (mg/kg)	Route	Source	As printed
10–20	IV	BSAVA Small Animal Formulary, 10th ed — Part A (Canine and Feline)p.44	10-20 mg/kg i.v., i.m., s.c., p.o. q6-8h. Amprolium (Harkers Pigeon Coccidiosis Treatmen
10–20	IV	Papich Saunders Handbook of Veterinary Drugs, 4th edp.73	• 10-20 mg/kg q6-8h IV, IM, or SQ or 20-40 mg/kg q8h PO. Doses as high as
20–40	IV	Papich Saunders Handbook of Veterinary Drugs, 4th edp.73	• 10-20 mg/kg q6-8h IV, IM, or SQ or 20-40 mg/kg q8h PO. Doses as high as
100

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Mechanism of action

Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins. Broader spectrum than penicillin G with gram-negative coverage.

Side effects & warnings

CONTRAINDICATED in rabbits, guinea pigs, and hamsters (fatal dysbiosis). May cause GI upset. Cross-reactivity with other beta-lactams. IM injection may be painful.

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 Ampicillin for Cats?

Ampicillin dose range in cats, with cited source references: IV 22–40 mg/kg q6-8h. Reference ranges from cited sources — verify against current literature before clinical use.

How is Ampicillin administered in Cats?

Documented routes for Ampicillin in cats: IV.

How long is Ampicillin given in Cats?

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

What conditions does Ampicillin treat in Cats?

Ampicillin is indicated in cats for: Surgical prophylaxis, bacteremia.

What are the side effects of Ampicillin in Cats?

These are general warnings for Ampicillin across species; consult the cat dosing table above for species-specific guidance. CONTRAINDICATED in rabbits, guinea pigs, and hamsters (fatal dysbiosis). May cause GI upset. Cross-reactivity with other beta-lactams. IM injection may be painful.

Other Antibiotic drugs with cat dosing

Amikacin Amoxicillin Amoxicillin Injectable Amoxicillin-Clavulanate Azithromycin Bacitracin Carbenicillin Cefaclor Cefadroxil Cefazolin Cefdinir Cefepime

Ampicillin dosing in other species

African Grey Parrots Amazon Parrots Ball Pythons Bearded Dragons Bettas Blue-tongue Skinks Canaries Cattle

See all species for Ampicillin See all drugs for Cats

Why a species-specific page? Ampicillin 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.