Ampicillin for Horses

Equine · Equus caballus · typical adult weight 350.00–700.00 kg

Ampicillin is dosed at 10–20 mg/kg IV q6-8h in horses, 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 horses for Susceptible bacterial infections, Bacterial infection. Routes documented in horses: IV. A typical adult horse weighs 350.00–700.00 kg. ExoticRx lists 2 cited dose rules for Ampicillin in horses, 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	10–20 mg/kg	q6-8h	5-10 days	Susceptible bacterial infections	Moderate	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
IV	10–22 mg/kg	q6-8h	5-7 days	Bacterial infection	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.

Printed doses in mg/kg for this drug and species, by source
Dose (mg/kg)	Route	Source	As printed
6.6	IM	Papich Saunders Handbook of Veterinary Drugs, 4th edp.75	• 6.6 mg/kg up to 10-20 mg/kg q6-8hr, IM or IV.
10–20	IM	Papich Saunders Handbook of Veterinary Drugs, 4th edp.75	• 6.6 mg/kg up to 10-20 mg/kg q6-8hr, IM or IV.
25–40	—	Papich Saunders Handbook of Veterinary Drugs, 4th edp.73	• Refractory infections: up to 25-40 mg/kg q6-8h.

Figures are transcribed from the cited page or table of each held edition and are shown for reference only. They are not dose recommendations, they do not feed the calculator, and none has been reviewed by a veterinarian.

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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 horses 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 Horses?

Ampicillin dose ranges in horses, with cited source references: IV 10–20 mg/kg q6-8h; IV 10–22 mg/kg q6-8h. Reference ranges from cited sources — verify against current literature before clinical use.

How is Ampicillin administered in Horses?

Documented routes for Ampicillin in horses: IV.

How long is Ampicillin given in Horses?

Cited course lengths for Ampicillin in horses include: 5-10 days; 5-7 days. Duration depends on the indication — match it to the specific dose rule in the table above.

What conditions does Ampicillin treat in Horses?

Ampicillin is indicated in horses for: Susceptible bacterial infections, Bacterial infection.

What are the side effects of Ampicillin in Horses?

These are general warnings for Ampicillin across species; consult the horse 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 horse dosing

Amikacin Amoxicillin Azithromycin Ceftiofur Chloramphenicol Doxycycline Enrofloxacin Erythromycin Gentamicin Marbofloxacin (Livestock)Metronidazole Oxytetracycline

Ampicillin dosing in other species

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

See all species for Ampicillin See all drugs for Horses

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 horses — 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.