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Antibiotic — Polymyxin (Last-Resort) Pregnancy: There are no adequate data from the use of colistimethate sodium in pregnant women. Single-dose studies in human pregnancy show that colistimethate sodium crosses the placental barrier, and there may be a risk of foetal toxicity if repeated doses are given to pregnant patients. Animal studies are insufficient with respect to effects on reproduction and development. Colistimethate sodium should be used in pregnancy only if the benefit to the mother outweighs the potential risk to the fetus. It is secreted in breast milk and should be administered to breastfeeding women only when clearly needed.

Colistin (Polymyxin E — XDR Burns Infection)

Brand names: Colomycin, Colistin Sulfomethate

Colistin (polymyxin E) is a last-line polymyxin antibiotic reserved for serious infections caused by extensively drug-resistant Gram-negative organisms, including in colonised or infected burns.

Adult dose

Dose: SCOPE — SYSTEMIC (INTRAVENOUS) TREATMENT ONLY. Adults and adolescents: maintenance dose 9 million IU/day of colistimethate sodium in 2-3 divided doses. In patients who are critically ill, a loading dose of 9 MIU should be administered
Route: Intravenous — administered as a slow infusion over 30-60 minutes. Patients with a totally implantable venous access device (TIVAD) in place may tolerate a bolus injection of up to 2 million units in 10 ml given over a minimum of 5 minutes. The dose must be prescribed and administered in the EU only as IU
Frequency: Maintenance 9 million IU/day divided into 2-3 doses. The loading dose is given once; the SPC states that the most appropriate time interval to the first maintenance dose has not been established. The loading dose applies to patients with normal AND impaired renal function, including those on renal replacement therapy
Max: 9 million IU/day is the recommended adult and adolescent maintenance dose, and the SPC gives no higher recommended figure. It notes that modelling suggests loading and maintenance doses of up to 12 MIU may be required in patients with good renal function in some cases, but states that clinical experience with such doses is extremely limited and safety has not been established; it also states there are limited safety data for the use of high doses above 6 MIU/day. Dose reductions are required when creatinine clearance is below 50 ml/min
THE FIGURES ABOVE ARE THE SYSTEMIC IV REGIMEN ONLY. The same SPC contains two other regimens that are NOT this page's route and must not be substituted: aerosol inhalation (adults, adolescents and children 2 years and over: 1-2 MIU two to three times per day, max 6 MIU/day; children under 2 years: 0.5-1 MIU twice daily, max 2 MIU/day) and intraventricular administration in adults (125,000 IU/day, with intrathecally administered doses not to exceed those recommended for intraventricular use). INDICATION: the SPC's §4.1 indication text was not captured in this bundle and the SPC does not name burns; the systemic posology above is the product's single systemic regimen, and §4.4 states 'Colistimethate sodium should only be used when other, more commonly prescribed antibiotics are not effective or not appropriate' — the last-resort framing this page describes. §4.4 also advises co-administering intravenous colistimethate sodium with another antibacterial agent whenever possible, taking into account the remaining susceptibilities of the pathogen(s), because resistance to intravenous colistin has been reported in particular when used as monotherapy. The SPC states the dose recommendations are based on limited population-pharmacokinetic data in critically ill patients, that therapeutic guidelines should be adhered to, and that there are limited clinical data on the efficacy and safety of intravenous colistimethate sodium. POTENCY UNITS: in the EU the dose of colistimethate sodium (CMS) must be prescribed and administered only as IU, because confusion between the different expressions of potency (IU, mg CMS, mg colistin base activity) has caused medication errors. The SPC carries a CMS conversion table; its columns were flattened in this source capture and their order cannot be reliably reconstructed here (the footnote 'Nominal potency of the drug substance = 12,500 IU/mg' contradicts the captured column order), so NO mg conversion is reproduced on this page — read the conversion table in the SPC itself. ELDERLY: no dose adjustments are considered necessary in older patients with normal renal function. HEPATIC IMPAIRMENT: there are no data in patients with hepatic impairment; caution is advised. PREPARATION: reconstitution of the required dose must use strict aseptic technique, particularly where multiple vials must be combined; colistimethate sodium undergoes hydrolysis to the active substance colistin in aqueous solution.

Paediatric dose

Dose: Children weighing 40 kg or less: 75,000-150,000 IU/kg/day divided into 3 doses. This is a DAILY TOTAL that is then divided into 3 doses — it is not a per-dose figure. For children with a body weight above 40 kg, use of the dosing recommendation for adults should be considered
Route: Intravenous — slow infusion over 30-60 minutes (systemic treatment). No paediatric dosing recommendation can be made for the intrathecal or intraventricular routes
Frequency: Divided into 3 doses per day
Max: No absolute paediatric ceiling is stated. The SPC records that the use of doses above 150,000 IU/kg/day has been reported in children with cystic fibrosis, and that for children above 40 kg the adult dosing recommendation should be considered
This is the label's own paediatric figure — nothing has been scaled from the adult dose. §4.2 verbatim: 'The data supporting the dose regimen in paediatric patients are very limited. Renal maturity should be taken into consideration when selecting the dose. The dose should be based on lean body weight. Children ≤ 40kg 75,000-150,000 IU/kg/day divided into 3 doses. For children with a body weight above 40 kg, use of the dosing recommendation for adults should be considered. The use of doses >150,000 IU/kg/day has been reported in children with cystic fibrosis. There are no data regarding the use or magnitude of a loading dose in critically ill children. No dose recommendations have been established in children with impaired renal function.' The SPC gives a RANGE rather than a single number, so dosePerKg is deliberately left null and the weight calculator is not offered — a range cannot be multiplied out safely, and the figure is a per-DAY total, not a per-dose amount. The dose should be based on LEAN body weight. §4.4 adds: caution is advised when administering colistimethate sodium to infants under 1 year of age as renal function is not fully mature in this age group, and the effect of immature renal and metabolic function on the conversion of colistimethate sodium to colistin is not known.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance, to colistin, or to polymyxin B

Side effects

  • Systemic treatment — neurotoxicity: apnoea, transient sensory disturbances such as facial paraesthesia and vertigo and, rarely, vasomotor instability, slurred speech, visual disturbances, confusion or psychosis. Neurological events have been reported in up to 27% of cystic fibrosis patients; these are generally mild and resolve during or shortly after treatment
  • Systemic treatment — nephrotoxicity: adverse effects on renal function, usually after higher than recommended doses in patients with normal renal function, failure to reduce the dose in renal impairment, or concomitant use of other nephrotoxic drugs; usually reversible on discontinuation. Rare (less than 1%) in cystic fibrosis patients treated within recommended dosage limits, but reported in approximately 20% of seriously ill hospitalised non-CF patients
  • Pseudo-Bartter syndrome has been reported after intravenous administration, with unknown frequency
  • Hypersensitivity reactions including skin rash and drug fever — withdraw treatment if these occur
  • Local irritation at the site of injection
  • Inhalation treatment (a different route, listed for completeness): coughing or bronchospasm; sore throat or mouth, which may be due to Candida albicans infection or hypersensitivity; skin rash
  • NOTE: the likelihood of adverse events may be related to the age, renal function and condition of the patient

Monitoring

  • Renal function monitoring should be performed at the start of treatment and regularly during treatment in ALL patients, and the dose adjusted according to creatinine clearance
  • Renal dose reductions (twice daily dosing recommended) — creatinine clearance under 50 down to 30 ml/min: 5.5-7.5 MIU/day; under 30 down to 10 ml/min: 4.5-5.5 MIU/day; under 10 ml/min: 3.5 MIU/day. The SPC states these are guidance only, as pharmacokinetic data in renal impairment are very limited
  • Haemodialysis (firm recommendations cannot be made; regimens that could be considered) — non-HD days 2.25 MIU/day (2.2-2.3 MIU/day), HD days 3 MIU/day given AFTER the haemodialysis session; twice daily dosing recommended
  • CVVHF / CVVHDF — as in patients with normal renal function; three times daily dosing recommended
  • Patients who are hypovolaemic or receiving other potentially nephrotoxic drugs are at increased risk of nephrotoxicity; nephrotoxicity has been reported to be associated with cumulative dose and treatment duration in some studies, so the benefit of prolonged treatment should be balanced against the increased risk of renal toxicity
  • Monitor for perioral paraesthesia and paraesthesia in the extremities — these are signs of overdose. High serum concentrations, from overdose or failure to reduce the dose in renal impairment, have led to facial paraesthesia, muscle weakness, vertigo, slurred speech, vasomotor instability, visual disturbances, confusion, psychosis and apnoea
  • Monitor serum electrolytes if pseudo-Bartter syndrome is suspected; normalisation may not be achieved without discontinuing colistimethate sodium
  • Discontinue immediately and implement appropriate measures in case of an allergic reaction
  • Consider co-administration with another antibacterial agent to prevent the emergence of resistance

Clinical monograph

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.

Reference: EUCAST/ESCMID Colistin Guidelines; BBA Burns Infection Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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