Polymyxin B and Colistin
Also known as: PolymyxinE, Colistin, Colistimethate
Polymyxins are older cyclic lipopeptide antibiotics reserved for selected serious Gram-negative infections when safer active options are limited. Kidney toxicity and neurological effects constrain use.
Quick Facts
Class, history and prodrug identity
Polymyxin B and colistin were discovered in the 1940s and became less common because of toxicity. Multidrug-resistant Gram-negative organisms, including carbapenem-resistant Acinetobacter, Pseudomonas and Klebsiella, renewed their last-resort role.
Colistin is polymyxin E. Systemic treatment uses the inactive prodrug colistimethate, converted to active colistin in the body. Polymyxin B and colistimethate have longstanding FDA approvals. Injectable routes include IV/IM; polymyxin B also appears in topical and ophthalmic combination products.
Membrane disruption and trial context
The positively charged cyclic structure binds lipidA in Gram-negative lipopolysaccharide, displacing stabilizing magnesium/calcium ions. Permeabilization of outer and inner membranes allows contents to leak, killing the organism. Polymyxins also bind and neutralize circulating endotoxin.
This Gram-negative membrane target explains their organism-specific role. In AIDA, adding a carbapenem to colistin did not improve outcomes over colistin alone for serious carbapenem-resistant infection. Optimizing exposure remains a balance between antibacterial activity and renal injury.
Sources: [1]
Approvals and treatment setting
Both agents are approved for susceptible serious Gram-negative infections and are generally reserved for situations with few safer active drugs. The topical/eye uses of polymyxin B remain separate from systemic last-resort treatment.
| Injectable product | Label warning |
|---|---|
| Polymyxin B | Boxed nephrotoxicity/neurotoxicity warning, including respiratory paralysis from neuromuscular blockade. |
| Colistimethate | Warnings for the same risks, but not in boxed form. |
Sources: [2]
Toxicity and monitoring
Renal injury is the principal dose-limiting effect and may become substantial acute kidney injury. Neurotoxicity includes numbness, tingling and dizziness. Neuromuscular blockade can impair breathing, especially alongside other drugs with that effect. Toxicity and susceptibility-guided selection prevent treating these agents as general antimicrobial supplements.
References and further reading
This reference draws on Superpower’s Peptide Library and the research linked below. Peptide Dossier’s editorial team adapted and integrated the material on .
- 10.1016/S1473-3099(18)30099-9Membrane disruption and trial contextCited in: Membrane disruption and trial context
- drugs.comApprovals and treatment settingCited in: Approvals and treatment setting
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Disclaimer: This article is for informational and educational purposes only. It is not intended as medical advice. The information presented is based on published research and should not be used as a substitute for professional medical guidance. Always consult a qualified healthcare provider before starting any peptide protocol. Some peptides discussed may not be approved for human use by the FDA or equivalent regulatory bodies.