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Antibiotic — Polymyxin (Last-Resort) Pregnancy: Avoid — nephrotoxicity and neurotoxicity risks; use only in life-threatening XDR infection

Colistin (Polymyxin E — XDR Burns Infection)

Brand names: Colomycin, Colistin Sulfomethate

Adult dose

Dose: Loading: 9 million units IV; Maintenance: 4.5 million units IV every 12 hours
Route: IV infusion over 30–60 min
Frequency: Every 12 hours
Max: 9 million units/day (or per TDM guidance)
LAST-RESORT antibiotic for XDR (extensively drug-resistant) Gram-negatives: carbapenem-resistant Pseudomonas, Acinetobacter baumannii, Klebsiella pneumoniae (CRE). Colistin is a prodrug (colistin sulfomethate) — converted to active colistin in vivo. Use only with ID specialist guidance and TDM.

Paediatric dose

Dose: 75000–150000 units/day/kg
Route: IV
Frequency: Divided every 8–12 hours
Max: 9 million units/day
Seek specialist/ID opinion — limited paediatric data. 75,000–150,000 units/kg/day in divided doses.

Dose adjustments

Renal

Significant dose reduction required in renal impairment — primary route of elimination is renal. TDM mandatory.

Hepatic

No specific adjustment.

Paediatric weight-based calculator

Seek specialist/ID opinion — limited paediatric data. 75,000–150,000 units/kg/day in divided doses.

Clinical pearls

  • Nephrotoxicity occurs in up to 50% — monitor creatinine daily. Consider renal replacement therapy threshold planning.
  • Always use combination therapy for XDR organisms — colistin + meropenem (despite resistance, meropenem may restore synergy at higher doses) or colistin + rifampicin
  • Prescribe in 'million units' — confusion between mg and units has caused fatal overdoses. 1 million units ≈ 80 mg colistin base activity (CBA)

Contraindications

  • Hypersensitivity to colistin or polymyxins
  • Myasthenia gravis (relative — neuromuscular blockade risk)

Side effects

  • Nephrotoxicity (major — occurs in 30–50% of patients)
  • Neurotoxicity (paraesthesia, dizziness, ataxia, respiratory muscle weakness)
  • Bronchospasm (inhaled formulation)
  • Anaphylaxis (rare)

Interactions

  • Aminoglycosides (additive nephrotoxicity — avoid if possible)
  • NMB agents (potentiation)
  • Loop diuretics (additive nephrotoxicity)
  • Cephalothin (additive nephrotoxicity)

Monitoring

  • Serum creatinine daily
  • Colistin TDM (target Css avg 2–4 mg/L)
  • Neurological assessment
  • Culture sensitivity — check for developing resistance

Reference: BNFc; BNF 90; EUCAST/ESCMID Colistin Guidelines; BBA Burns Infection Guidelines; BNFc. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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