Colistin

also known as: Polymyxin E, Colistimethate Sodium, CMS

Polymyxin B's sibling — a cyclic lipopeptide antibiotic revived from the 1950s as the ultimate weapon against pan-drug-resistant gram-negative bacteria, despite significant nephrotoxicity.

A cyclic lipopeptide antibiotic (polymyxin E) administered as the inactive prodrug colistimethate sodium (CMS), with the same LPS-disrupting mechanism as polymyxin B but different pharmacokinetics due to prodrug conversion.

Mechanism of action

Same as polymyxin B: cationic peptide ring displaces divalent cations from LPS, destabilizing the gram-negative outer membrane and causing cell lysis. Also binds and neutralizes circulating endotoxin. Administered as the prodrug CMS (colistimethate), which is hydrolyzed to active colistin in vivo.

Primary uses

Multidrug-resistant gram-negative infections
Cystic fibrosis chronic Pseudomonas suppression (inhaled)
Carbapenem-resistant Enterobacteriaceae
Ventilator-associated pneumonia (MDR pathogens)

Typical dosing

2.5–5 mg/kg/day CBA divided every 8–12 hours (IV) or twice daily (inhaled) (intravenous or inhaled)

Dosing expressed as colistin base activity (CBA). Loading dose recommended for serious infections. Nephrotoxicity in 20–60% of patients.

Regulatory status

FDA-approved (original approval 1959). Available as colistimethate sodium for injection and inhalation. Used for multidrug-resistant gram-negative infections, particularly in cystic fibrosis (inhaled).

References

[review] Nation RL, et al. "Colistin in the 21st century." Curr Opin Infect Dis, 2009;22:535-543.

Related peptides

Polymyxin B

The gram-negative last resort — a cyclic lipopeptide antibiotic revived from the 1950s as a critical weapon against carbapenem-resistant Acinetobacter, Pseudomonas, and Klebsiella.

Daptomycin

A last-resort lipopeptide antibiotic — the first-in-class cyclic peptide that kills MRSA and VRE by depolarizing bacterial membranes, without resistance through traditional mechanisms.

LL-37

The only human cathelicidin — an antimicrobial peptide with direct activity against bacteria, fungi, viruses, and biofilms, with additional roles in wound healing and immune signaling.

Disclaimer

This entry is for educational purposes only and does not constitute medical advice. Dosing information reflects published regulatory or research data and is not a recommendation. Many compounds described here are not approved for human use in the United States. Consult a licensed medical professional before considering any peptide therapy.