[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Polymyxins](https://durgical.com/en/pharmacology/classes/polymyxins/) › Polymyxin B

[Pharmacology](https://durgical.com/en/pharmacology/) · [Polymyxins](https://durgical.com/en/pharmacology/classes/polymyxins/)

# Polymyxin B

A polymyxin given IV, IM or intrathecally for resistant gram-negatives, and used topically in eye and ear drops; nephrotoxic and neurotoxic.

Updated 2026-11-01

- Class: [Polymyxins](https://durgical.com/en/pharmacology/classes/polymyxins/)
- Target: Lipid A of the lipopolysaccharide, gram-negative outer membrane
- ATC code: J01XB02
- WHO Model List of Essential Medicines

## Mechanism of action

Polymyxin B binds the lipid A of lipopolysaccharide and the phospholipids of the cell membrane and increases its permeability, killing almost all gram-negative bacilli except the Proteus group. Unlike colistimethate, it is given directly in its active form.

- Binds lipid A and membrane phospholipids
- Membrane permeability rises
- The gram-negative bacillus dies

## Pharmacokinetics

**Absorption**
Not absorbed from the gut or intact skin; given IV, IM, intrathecally or topically.

**Distribution**
Loses much of its activity in the presence of serum, so blood levels of active drug are low; in meningitis it is given only intrathecally.

**Elimination**
Mainly by non-renal routes.

## Indications

- Serious infections by Pseudomonas aeruginosa and other multidrug-resistant gram-negatives (bloodstream, urinary tract). [MRSA and other multidrug-resistant organism infections →](https://durgical.com/en/conditions/mrsa-and-other-multidrug-resistant-organism-infections/)
- Gram-negative bacteremia and sepsis. [Sepsis and septic shock →](https://durgical.com/en/conditions/sepsis-and-septic-shock/)
- Meningitis by Pseudomonas or Haemophilus influenzae, by the intrathecal route. [Bacterial meningitis →](https://durgical.com/en/conditions/bacterial-meningitis/)
- Topical eye and ear infections, usually combined with other antibiotics. [Otitis externa →](https://durgical.com/en/conditions/otitis-externa/)

## Adverse effects

### Common

- Facial flushing, dizziness, drowsiness, circumoral and stocking-glove paresthesia
- Severe pain at intramuscular sites; thrombophlebitis at IV sites
- Drug fever, urticarial rash
- Meningeal irritation after intrathecal use

### Serious (rare, important)

- Nephrotoxicity: albuminuria, cellular casts, azotemia
- Neurotoxicity: irritability, weakness, ataxia, blurred vision
- Respiratory paralysis from neuromuscular blockade, especially after anaesthesia or muscle relaxants
- Clostridioides difficile diarrhoea

## Contraindications

- Previous hypersensitivity to polymyxins

## Key interactions

**Aminoglycosides, colistin, bacitracin, vancomycin and other nephrotoxic or neurotoxic drugs**
Added kidney and nerve damage; avoided at the same time or in sequence.

**Curare-like relaxants, succinylcholine, ether, sodium citrate**
Can precipitate respiratory depression.

## What is monitored

- Kidney function before and during treatment; urinalysis for albumin and casts
- Neurological signs and breathing
- Cerebrospinal fluid cultures and glucose during intrathecal treatment

## Administration and safety

- IM and intrathecal use only in hospitalized patients under constant supervision.
- IM injection is not routine because it is very painful, especially in children.
- Doses are written in units: check units carefully against the order.
- Inspect IV sites for thrombophlebitis.

## Nursing care

- Baseline creatinine and urinalysis; daily intake and output.
- Watch for perioral numbness, drowsiness, weakness or shallow breathing.
- Extra caution after anaesthesia or with muscle relaxants.
- Teaching: report numbness, vision change, less urine or trouble breathing.

## Pregnancy and breastfeeding

Safety in human pregnancy has not been established; systemic use is reserved for situations without safer alternatives.

## Memory aid

Polymyxin «B» for «Burst the Bilayer»: active from the start (no prodrug), cleared outside the kidney, but still Bad for the kidney.

## Test yourself

Think of the answer, then tap the question to see it.

## How is polymyxin B meningitis treatment given, and why?

Only by the intrathecal route, directly into the cerebrospinal fluid; the label reserves meningeal treatment to this route.

## Which group of gram-negative bacilli does polymyxin B not kill?

The Proteus group (Serratia is also resistant to polymyxins).

## What is a key pharmacological difference between polymyxin B and colistimethate?

Polymyxin B is given in active form and cleared mostly outside the kidney; colistimethate is a prodrug cleared by the kidney.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/polymyxin-b/)

## Related drugs

- [Colistin (colistimethate)](https://durgical.com/en/pharmacology/colistin/)
- [Gentamicin](https://durgical.com/en/pharmacology/gentamicin/)
- [Vancomycin](https://durgical.com/en/pharmacology/vancomycin/)

## Related conditions

- [MRSA and other multidrug-resistant organism infections](https://durgical.com/en/conditions/mrsa-and-other-multidrug-resistant-organism-infections/)
- [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/)
- [Bacterial meningitis](https://durgical.com/en/conditions/bacterial-meningitis/)
- [Otitis externa](https://durgical.com/en/conditions/otitis-externa/)

[← Back to the class: Polymyxins](https://durgical.com/en/pharmacology/classes/polymyxins/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - POLYMYXIN B- polymyxin b sulfate injection, powder, for solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b56f18c0-ef5e-4ed9-a5af-f79f3cd189b6) (DailyMed (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 59 (McGraw Hill, 2023).

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Representative model, for educational purposes only.

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