Indications Colistimethate (CMS) is indicated for the treatment of acute or chronic infections caused by sensitive strains of certain Gram‑negative bacilli. It is particularly effective against Pseudomonas aeruginosa. It is not indicated for infections due to Proteus or Neisseria. Effective against Enterobacter aerogenes, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa.

Composition Each vial contains:

Colistimethate Sodium 1 MIU (≈34 mg Colistin)
Colistimethate Sodium 2 MIU (≈68 mg Colistin)
Colistimethate Sodium 3 MIU (≈102 mg Colistin)
Colistimethate Sodium 4.5 MIU (≈150 mg Colistin)

Description Colistimethate (CMS) is a surface‑active agent that penetrates and disrupts the bacterial cell membrane, exhibiting bactericidal activity against aerobic Gram‑negative microorganisms such as Enterobacter aerogenes, E. coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa.

Pharmacology Colistimethate is polycationic with hydrophobic and lipophilic properties. It interacts with bacterial cytoplasmic membranes, altering permeability and causing cell death. Polymyxins may also enter the cell and precipitate cytoplasmic components, mainly ribosomes.

Dosage

Maintenance dose: 9 MIU/day in 2–3 divided doses.
Critically ill patients: Loading dose of 9 MIU recommended.

Renal impairment: Dose reduction required when creatinine clearance <50 mL/min. Twice‑daily dosing recommended.

Creatinine Clearance	Daily Dose
50–30 mL/min	5.5–7.5 MIU
30–10 mL/min	4.5–5.5 MIU
<10 mL/min	3.5 MIU

Hemodialysis patients:

Non‑HD days: 2.25 MIU/day
HD days: 3 MIU/day (after dialysis)

Pediatric population:

<40 kg: 75,000–150,000 IU/kg/day in 3 divided doses.
40 kg: >150,000 IU/kg/day (especially in cystic fibrosis).

Hepatic impairment: No data available; use with caution.

Administration

Direct intermittent: Inject half of total daily dose slowly over 3–5 minutes every 12 hours.
Continuous infusion: Inject half over 3–5 minutes, then dilute remaining half in one of the following solutions:
- 0.9% NaCl
- 5% dextrose in 0.9% NaCl
- 5% dextrose in water
- 5% dextrose in 0.45% NaCl
- 5% dextrose in 0.225% NaCl
- Lactated Ringer’s solution

Administer second half by slow IV infusion over 22–23 hours, starting 1–2 hours after initial dose. Reduce infusion rate in renal impairment. Prepare fresh solution; use within 24 hours.

Alternative method: Dilute prescribed dose in 50–100 mL 0.9% NaCl and infuse IV over 30–60 minutes.

Interaction Avoid concomitant use with:

Aminoglycosides or other polymyxins (neuromuscular blockade risk).
Muscle relaxants (e.g., tubocurarine, succinylcholine, gallamine, decamethonium).
Sodium cephalothin (increased toxicity risk).

Contraindications Contraindicated in patients with known hypersensitivity to colistimethate sodium or any component of the formulation.