Polymyxin B: veterinary dose and monograph

At a glance

Drug class

Antibiotic

Also known as

Polymyxin B sulphate, Neosporin (component), Otibact (component)

Species with doses

Dogs, Cats and Horses

Routes

IV, Topical

Last reviewed

1 October 2026

Indications

• Topical/ophthalmic/otic Gram-negative infection (triple-antibiotic preparations) including Pseudomonas
• Adjunctive ANTI-ENDOTOXIC therapy in endotoxaemia (low-dose, horses/cattle — e.g. colitis, sepsis, grain overload)
• Surface Gram-negative skin/eye/ear infections

Polymyxin B dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Topical / ophthalmic / otic Gram-negative infection: Covers Pseudomonas. Systemic polymyxin (Papich 5e: 15,000–25,000 U/kg q12h IV) is nephro- and neurotoxic and rarely justified.

Cats

• Topical Gram-negative infection (caution): Neomycin–polymyxin B–bacitracin ophthalmic preparations have been associated with fatal anaphylaxis in cats; prefer alternatives. Systemic use is not recommended.

Cattle

• No reference dose for this species: Neither Papich 5e nor Plumb’s gives a polymyxin B dose for cattle.

Horses

• Anti-endotoxic adjunct (endotoxaemia): UNITS/kg. Papich 5e: 1000–10,000 U/kg (usually 6000 U/kg ≈ 1 mg/kg) IV q8h, e.g. in 1 L saline over 15 min for five treatments. Nephrotoxic — ensure hydration and monitor creatinine, especially in azotaemic or neonatal horses.

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• No reference dose for this species: Neither Papich 5e nor Plumb’s gives a polymyxin B dose for cattle.

Contraindications

Systemic use except as a deliberate, monitored low-dose anti-endotoxic adjunct (nephro-/neurotoxicity; stewardship). Renal impairment (systemic). Perforated tympanic membrane for some otic preparations (verify). Known hypersensitivity.

Species-specific warnings

Horses: Low-dose IV polymyxin B for endotoxaemia must be given slowly with renal monitoring — higher doses are nephro-/neurotoxic.

Adverse effects

• Topical: local irritation/hypersensitivity
• Systemic: nephrotoxicity, neurotoxicity (paraesthesia, neuromuscular blockade)
• Ototoxicity (with eardrum perforation)

Drug interactions

• Aminoglycosides / amphotericin B / NSAIDs: additive nephrotoxicity (systemic use)
• Neuromuscular blockers / anaesthetics: potentiated neuromuscular blockade (systemic)
• Often combined with neomycin/bacitracin topically (complementary spectrum)

Pregnancy and lactation

Topical use gives negligible systemic exposure (low risk). Avoid systemic use in pregnancy unless essential.

Monitoring

• Local response/irritation (topical)
• Renal function and neurologic status (any systemic use)
• Clinical course of endotoxaemia (adjunct only — fluids/anti-inflammatories are primary)
• Eardrum integrity before otic use

Toxicity and overdose

Topical use is well tolerated (local irritation only). SYSTEMIC polymyxin B is dose-limited by nephrotoxicity and neurotoxicity (paraesthesia, ataxia, neuromuscular blockade/apnoea) — the same profile as colistin — hence systemic use is restricted to deliberate low-dose anti-endotoxic protocols with monitoring.

Management: For systemic toxicity: discontinue; supportive care, IV fluids and renal support; ventilatory support for neuromuscular blockade (anticholinesterases unreliable for polymyxin blockade). No specific antidote. Topical overdose: rinse/discontinue.

Clinical pearls

• In small animals it is essentially a TOPICAL Gram-negative (incl. Pseudomonas) agent — the "polymyxin" in triple-antibiotic eye/ear/skin products
• Its lipid-A binding lets low-dose IV polymyxin B mop up ENDOTOXIN in equine/bovine endotoxaemia (an adjunct to fluids and flunixin, not a stand-alone)
• Systemic polymyxins are nephro-/neurotoxic and stewardship-sensitive (relative of colistin) — keep systemic use low-dose and monitored
• Check the tympanic membrane before using polymyxin-containing otic drops

Mechanism of action

A cationic polymyxin that binds the lipid-A region of Gram-negative lipopolysaccharide, disrupting the outer and cytoplasmic membranes (detergent-like, concentration-dependent bactericidal effect). The same lipid-A binding NEUTRALISES free endotoxin, blocking its inflammatory signalling — the rationale for low-dose anti-endotoxic use in endotoxaemia. Poor systemic absorption from topical sites limits toxicity to local effects.

Formulations and products

• Topical/ophthalmic combination (with neomycin ± bacitracin/dexamethasone)
• Injection (systemic, IU-based — rare)
• Otic/ophthalmic combinations (Various) — Polymyxin B + neomycin ± bacitracin/dexamethasone, Eye/ear/skin preparation
• Neosporin / Polymyxin-B — Polymyxin B + neomycin + bacitracin (topical); 500,000 IU vial (systemic), Topical / injection (human-label)

Storage

Topical/ophthalmic/otic products: 15–30 °C per label. Reconstituted systemic solution: refrigerate, use promptly.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

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Frequently asked questions