Colistin (Polymyxin E — XDR Burns Infection)

How it works

It binds the lipopolysaccharide of the Gram-negative outer membrane, disrupting membrane integrity and causing bacterial cell death; it has no activity against Gram-positive organisms.

Prescribing in practice

• Dose-related nephrotoxicity is the principal hazard, so renal function must guide dosing and concurrent nephrotoxins should be minimised.
• Neurotoxicity, including paraesthesia and neuromuscular effects, can occur and may be potentiated by other neuromuscular-blocking agents.
• It is administered as the inactive prodrug colistimethate sodium, and dosing nomenclature is a recognised source of serious medication error so the units must be stated unambiguously.

Monitoring

Monitor renal function closely throughout therapy and watch for neurological symptoms.

Counselling the patient

• This is a reserved antibiotic used for highly resistant infections.
• Report any numbness, tingling, muscle weakness, or reduction in urine output to the team.

Evidence & guidelines

Colistin has re-emerged as a salvage agent for multidrug-resistant Gram-negative infection; its use is guided by stewardship principles given the toxicity and resistance concerns.