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Polymyxin antibiotic Pregnancy: §4.6: 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 the effect 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. Breast-feeding: colistimethate sodium is secreted in breast milk and should be given to breastfeeding women only when clearly needed.

Colistimethate sodium

Brand names: Promixin, Colomycin, Colobreathe

Colistimethate sodium is the inactive prodrug formulation of colistin (polymyxin E), a polymyxin antibiotic reserved for serious infections caused by multidrug-resistant Gram-negative bacteria and given intravenously or by nebulisation.

Adult dose

Dose: Serious infections due to selected aerobic Gram-negative pathogens in patients with limited treatment options (intravenous; adults and adolescents): maintenance dose 9 million IU/day (9 MIU/day) in 2-3 divided doses; in critically ill patients a loading dose of 9 MIU is given. Chronic pulmonary Pseudomonas aeruginosa infection in cystic fibrosis (nebulised inhalation; adults, adolescents and children aged 2 years and over): 1-2 MIU two to three times per day (max 6 MIU/day by inhalation). Doses are prescribed and given in International Units (IU) only, never in mg of colistin base activity.
Route: Intravenous (slow infusion over 30-60 minutes) and nebulised inhalation (Colomycin 1 million IU reconstituted with 3 mL of 0.9% sodium chloride and given through a suitable nebuliser)
Frequency: Intravenous: 2-3 divided doses per day; nebulised: two to three times per day
Routes NOT covered by this card: the page's inhaled dry-powder route (Colobreathe) has no source in this bundle; the Colomycin SPC also prints an intraventricular dose (125,000 IU/day in adults; intrathecal doses must not exceed the intraventricular dose) which is not carried here. No maximum is printed for the intravenous route (the label says modelling suggests loading and maintenance doses of up to 12 MIU may be required in some patients with good renal function, but clinical experience with such doses is extremely limited and safety has not been established, so no ceiling is stated); the 6 MIU/day maximum applies to the inhaled route only and is therefore not stored as a card-wide maximum. The loading dose applies to patients with normal and impaired renal function, including those on renal replacement therapy. The label advises considering co-administration of IV colistimethate with another antibacterial agent where possible, as resistance has been reported with monotherapy. Nebulised dose may be adjusted to severity and clinical response; follow clinical guidance on duration, periodicity and co-administration of other antibacterials. Patients with a totally implantable venous access device may tolerate a bolus injection of up to 2 million units in 10 mL over a minimum of 5 minutes. IU-vs-mg confusion has caused medication errors: the SPC conversion table is nominal and approximate only and no IU-to-mg conversion is asserted on this card. Elderly: no dose adjustment is considered necessary in older patients with normal renal function. Administer under the supervision of physicians with appropriate experience in its use.

Paediatric dose

Dose: Intravenous: children weighing 40 kg or less 75,000-150,000 IU/kg/day divided into 3 doses (based on lean body weight); for children above 40 kg consider the adult dosing recommendation. Nebulised (chronic Pseudomonas aeruginosa infection in cystic fibrosis): children aged 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).
Route: Intravenous infusion; nebulised inhalation
Frequency: Intravenous: divided into 3 doses per day; nebulised: as above
All figures printed in §4.2 of the Colomycin SPC. The label calls the paediatric intravenous data 'very limited' and says renal maturity should be taken into consideration when selecting the dose; caution is advised in infants under 1 year because renal function is not fully mature (§4.4). No neonate-specific regimen is printed in §4.2 and none is given here. Doses above 150,000 IU/kg/day have been reported in children with cystic fibrosis but are not a recommendation. No dose recommendations have been established in children with impaired renal function, and no specific intrathecal or intraventricular dosing recommendation can be made in children.

Dose adjustments

Renal

Intravenous: dose adjustments in renal impairment are necessary, although pharmacokinetic data are very limited and the following is guidance only. For creatinine clearance below 50 mL/min twice daily dosing is recommended, with total daily doses of: CrCl below 50 to 30 mL/min 5.5-7.5 MIU; below 30 to 10 mL/min 4.5-5.5 MIU; below 10 mL/min 3.5 MIU. Haemodialysis (firm recommendations cannot be made; regimens that could be considered): non-HD days 2.25 MIU/day, HD days 3 MIU/day given after the HD session, twice daily dosing. CVVHF/CVVHDF: as in patients with normal renal function, three times daily dosing. Paediatric: no dose recommendations have been established in children with impaired renal function. Inhalation: dose adjustment is not considered necessary, but caution is advised in renal impairment. §4.4: renal function monitoring should be performed at the start of treatment and regularly during treatment in all patients; hypovolaemic patients and those on other nephrotoxic drugs are at increased risk of nephrotoxicity.

Hepatic

Intravenous: there are no data in patients with hepatic impairment; caution is advised. Inhalation: dose adjustment is not considered necessary.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance, colistin or polymyxin B

Side effects

  • Neurotoxicity (systemic use): apnoea, transient sensory disturbances such as facial paraesthesia and vertigo, and rarely vasomotor instability, slurred speech, visual disturbances, confusion or psychosis - associated with overdose, failure to reduce the dose in renal insufficiency, or concomitant neuromuscular blocking drugs or other drugs with similar neurological effects; reducing the dose may alleviate symptoms. Neurological events have been reported in up to 27% of cystic fibrosis patients, generally mild
  • Nephrotoxicity: usually after higher than recommended doses in patients with normal renal function, failure to reduce the dose in renal impairment, or concomitant nephrotoxic drugs; usually reversible on discontinuation. Rare (less than 1%) in cystic fibrosis patients within recommended dosage limits; signs reported in approximately 20% of seriously ill hospitalised non-CF patients
  • Pseudo-Bartter syndrome after intravenous use (unknown frequency)
  • Hypersensitivity reactions including skin rash and drug fever - withdraw treatment if these occur
  • Local irritation at the injection site
  • Inhalation: coughing or bronchospasm; sore throat or mouth (may be due to Candida albicans infection or hypersensitivity)
  • Antibiotic-associated and pseudomembranous colitis (section 4.4)
  • Aseptic meningitis was the most commonly observed adverse effect with intrathecal/intraventricular administration (section 4.4)

Interactions

  • Other potentially nephrotoxic or neurotoxic medicines - concomitant use of intravenous colistimethate sodium should be undertaken with great caution
  • Other formulations of colistimethate sodium - caution; little experience and a possibility of summative toxicity
  • Non-depolarising muscle relaxants - section 4.5 attributes this to colistin's effect on acetylcholine release at the neuromuscular junction (the fetched interaction text is truncated at this point, so the full statement was not retrieved)
  • Drugs that inhibit or induce drug-metabolising enzymes, or are substrates of renal carrier mechanisms - potential for interaction should be borne in mind; colistimethate/colistin did not induce the CYP enzymes tested in vitro

Monitoring

  • Renal function at the start of treatment and regularly during treatment in all patients; adjust the dose to creatinine clearance
  • Perioral paraesthesia and paraesthesia in the extremities - signs of overdose
  • Serum electrolytes if pseudo-Bartter syndrome is suspected
  • Signs of hypersensitivity - stop treatment in an allergic reaction
  • Bronchospasm on inhalation - may be prevented or treated with beta-2 agonists; withdraw treatment if troublesome
  • Diarrhoea during or after use - consider antibiotic-associated or pseudomembranous colitis (Clostridium difficile); do not give medicines that inhibit peristalsis
  • Use with the greatest caution and only if clearly needed in myasthenia gravis; extreme caution in porphyria
  • Caution in infants under 1 year of age because renal function is not fully mature

Clinical monograph

How it works

After hydrolysis to colistin, it binds the lipopolysaccharide of the Gram-negative outer membrane, disrupting membrane integrity and causing bactericidal cell death.

Prescribing in practice

  • Dose-related nephrotoxicity and neurotoxicity are the principal hazards and dosing must be adjusted in renal impairment, with avoidance of other nephrotoxins where possible.
  • Nebulised use can provoke bronchospasm, so an initial dose under supervision and pre-treatment bronchodilation may be needed.
  • Different products and labelling conventions vary, so prescribe and dispense with care to avoid units-based errors.

Monitoring

Monitor renal function regularly throughout treatment and observe for neurological symptoms such as paraesthesia or confusion.

Counselling the patient

  • Report numbness, tingling, dizziness or reduced urine output.
  • With the inhaled form, tell the team if you become wheezy or short of breath after a dose.

Evidence & guidelines

Use is supported by product information and specialist guidance for multidrug-resistant Gram-negative infection.

Reference: 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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