[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/) › Colistin (colistimethate)

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

# Colistin (colistimethate)

A last-resort polymyxin for multidrug-resistant Pseudomonas, Acinetobacter and Klebsiella; it can injure the kidney and nerves and stop breathing.

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: J01XB01
- WHO Model List of Essential Medicines

Also called: polymyxin E, colistimethate sodium

## Mechanism of action

Colistin is a cationic peptide with a fatty tail. It binds the negatively charged lipid A of lipopolysaccharide, inserts into the outer and then the inner membrane, and disrupts them like a detergent; the bacterium leaks and dies. It is given as colistimethate, an inactive prodrug that is slowly converted to colistin in the blood.

- Colistimethate is converted to active colistin
- Binds lipid A of the outer membrane
- Disrupts the membranes like a detergent
- The gram-negative bacterium leaks and dies

## Pharmacokinetics

**Absorption**
Not absorbed by mouth; given IV, IM or by inhalation.

**Metabolism**
The prodrug colistimethate is hydrolysed slowly to active colistin; levels vary a lot between patients.

**Elimination**
The prodrug is cleared mainly by the kidney (which suits urinary infections); active colistin mostly by other routes.

**Half-life**
Serum levels fall with a half-life of about 2 to 3 hours after IV or IM colistimethate.

## Indications

- Serious infections by multidrug-resistant gram-negative bacilli (Pseudomonas aeruginosa, Acinetobacter, Klebsiella, Enterobacter, E. coli) when safer options fail. [MRSA and other multidrug-resistant organism infections →](https://durgical.com/en/conditions/mrsa-and-other-multidrug-resistant-organism-infections/)
- Urinary tract infections by multidrug-resistant gram-negatives (colistimethate reaches the urine well). [Urinary tract infection (acute cystitis) →](https://durgical.com/en/conditions/urinary-tract-infection/)
- Inhaled, as an adjunct in hospital-acquired pneumonia and in cystic fibrosis. [Cystic fibrosis →](https://durgical.com/en/conditions/cystic-fibrosis/)

## Adverse effects

### Common

- Tingling around the mouth and in the limbs, numbness, itching
- Dizziness, vertigo, slurred speech
- Gastrointestinal upset, fever, urticaria and rash

### Serious (rare, important)

- Nephrotoxicity (dose-related, usually reversible on stopping); less urine, rising creatinine
- Neuromuscular blockade with respiratory arrest and apnea, more likely with kidney failure
- Seizures; electrolyte and acid–base disorders (pseudo-Bartter syndrome)
- Clostridioides difficile diarrhoea

## Contraindications

- Hypersensitivity to colistimethate or polymyxins

## Key interactions

**Aminoglycosides and polymyxin B**
Added neuromuscular blockade and nephrotoxicity; concurrent use is avoided or done with extreme caution.

**Curare-like muscle relaxants, succinylcholine, anaesthetic agents, sodium citrate**
Potentiate the blockade: risk of respiratory paralysis.

**Vancomycin and other nephrotoxic drugs**
More kidney injury.

## What is monitored

- Creatinine and urine output at baseline and often during treatment
- Respiratory rate and muscle strength, especially after surgery
- Neurological symptoms (paresthesia, confusion, vertigo)
- Electrolytes

## Administration and safety

- Strength may be labelled as colistin base activity or in other units depending on the country and product: the unit is confirmed with pharmacy to avoid dosing errors.
- Reconstituted and given by slow IV injection, IV infusion or IM; the inhaled preparation is used only by nebulizer.

## Nursing care

- Before starting: kidney function, weight, other nephrotoxic drugs and planned anaesthesia.
- Record intake and output; report falling urine output or rising creatinine.
- Watch breathing and muscle weakness, especially after surgery or with relaxants.
- Teaching: tingling or dizziness may occur; avoid driving or using machinery while on it.

## Pregnancy and breastfeeding

Animal studies showed malformations at doses below the human dose, and human data are lacking; it is used in pregnancy only when no safer option exists.

## Memory aid

COLISTIN = «COLlapse the LIpid wall, STop the kidney and the breathing»: last resort, watch the Kidney, the Nerves and the lungs.

## Test yourself

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

## Why is colistin called a last-resort antibiotic?

It still works against many multidrug-resistant gram-negatives, but its kidney and nerve toxicity is high, so it is kept for when safer drugs fail.

## After surgery, a patient on colistimethate has shallow breathing and weakness. What has likely happened?

Neuromuscular blockade by colistin, potentiated by anaesthetics and muscle relaxants, which can lead to apnea.

## Why is colistimethate preferred over polymyxin B for urinary infections?

The prodrug colistimethate is cleared by the kidney and reaches the urine, while polymyxin B is cleared mostly by non-renal routes.

## Which organisms resist colistin naturally?

Proteus and Serratia (and Burkholderia), plus all gram-positive bacteria.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/colistin/)

## Related drugs

- [Polymyxin B](https://durgical.com/en/pharmacology/polymyxin-b/)
- [Meropenem](https://durgical.com/en/pharmacology/meropenem/)
- [Amikacin](https://durgical.com/en/pharmacology/amikacin/)
- [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/)
- [Urinary tract infection (acute cystitis)](https://durgical.com/en/conditions/urinary-tract-infection/)
- [Cystic fibrosis](https://durgical.com/en/conditions/cystic-fibrosis/)

[← 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 - COLISTIMETHATE- colistimethate sodium injection, powder, for solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8ec7dc90-825c-422e-9f4b-c8ace9d93af5) (DailyMed (U.S. National Library of Medicine), 2026); [Colistimethate Injection: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682860.html) (MedlinePlus (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 59 (McGraw Hill, 2023).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/pharmacology/colistin/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/colistin/