# Polymyxin B: veterinary dose and monograph

> Polymyxin B is a veterinary antibiotic. A polymyxin antibiotic active against Gram-negative bacteria (E. Indications include 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. This monograph lists 3 reference doses for dogs, cats and horses, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/polymyxin-b · Last reviewed: 2026-10-01

## 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

*Polymyxin B doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Topical / ophthalmic / otic Gram-negative infection | Apply the combination product to the eye, ear or skin per label (q6–12h) | Topical | q6–12h per product | — |

- 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

*Polymyxin B doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Topical Gram-negative infection (caution) | Topical product per label — avoid neomycin–polymyxin–bacitracin ophthalmic products in cats | Topical | per product | — |

- 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

*Polymyxin B doses for cattle*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| No reference dose for this species | Not established in Papich 5e or Plumb’s 10e — do not extrapolate from another species | — | — | — | — |

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

### Horses

*Polymyxin B doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Anti-endotoxic adjunct (endotoxaemia) | 1000–6000 mg/kg | IV | q8h (up to 5 treatments) | — |

- 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.

*Polymyxin B doses for buffalo*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| No reference dose for this species | Not established in Papich 5e or Plumb’s 10e — do not extrapolate from another species | — | — | — | — |

- 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

> **Caution:** 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

> **Caution:** 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.

## Other antibiotics

- [Ornidazole](https://vetmasterji.com/drugs/ornidazole)
- [Oxytetracycline](https://vetmasterji.com/drugs/oxytetracycline)
- [Penicillin G](https://vetmasterji.com/drugs/penicillin-g)
- [Pirlimycin](https://vetmasterji.com/drugs/pirlimycin)
- [Pradofloxacin](https://vetmasterji.com/drugs/pradofloxacin)
- [Procaine Penicillin G](https://vetmasterji.com/drugs/procaine-penicillin)
- [Rifampin](https://vetmasterji.com/drugs/rifampin)
- [Rifaximin](https://vetmasterji.com/drugs/rifaximin)

## Frequently asked questions

### What is the dose of Polymyxin B for dogs?

Reference doses for Polymyxin B in dogs: Apply the combination product to the eye, ear or skin per label (q6–12h) Topical q6–12h per product (Topical / ophthalmic / otic Gram-negative infection). Confirm against the label and the patient before use.

### What is the dose of Polymyxin B for cats?

Reference doses for Polymyxin B in cats: Topical product per label — avoid neomycin–polymyxin–bacitracin ophthalmic products in cats Topical per product (Topical Gram-negative infection (caution)). Confirm against the label and the patient before use.

### Can Polymyxin B be given to cattle?

Not established in Papich 5e or Plumb’s 10e — do not extrapolate from another species (No reference dose for this species).

### When should Polymyxin B not be used?

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.

### What are the side effects of Polymyxin B in animals?

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

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.