Polymyxins (Polymyxin B / Colistin)
Also known as: Polymyxin B, Colistin, Colistimethate, Coly-Mycin M, Polymyxin E
Last-resort cyclic peptide antibiotics for multidrug-resistant gram-negative infections. FDA-approved (polymyxin B, colistimethate). Prescription only.
Last updated
Mechanism of Action
Polymyxins are cationic cyclic lipopeptides. They bind the negatively charged lipid A of lipopolysaccharide in the outer membrane of gram-negative bacteria, displacing calcium and magnesium, which disrupts the outer and inner membranes and kills the cell. Colistin is given as an inactive prodrug, colistimethate, that converts to colistin in the body; polymyxin B is given in its active form. Resistance can arise from lipid A modification, including transferable mcr genes.
- Half-life
- Roughly 9–14 hours in critically ill adults; colistin varies with kidney function
- Administration Routes
- Intravenous, Intramuscular, Inhaled, Intrathecal, Topical
- Research Status
- Clinical
Reported Benefits
- Treat serious infections caused by carbapenem-resistant Acinetobacter, Pseudomonas and Enterobacterales when few options remain
- Inhaled colistimethate is used for chronic Pseudomonas lung infection in cystic fibrosis
- Polymyxin B is also used in topical and ophthalmic combination products
Potential Side Effects
- Kidney injury (common and dose-related; boxed warning)
- Neurotoxicity: numbness, tingling, dizziness
- Neuromuscular blockade and respiratory paralysis (rare, serious)
- Bronchospasm with inhaled use
Common Dosing
Intravenous polymyxins are given in hospital by clinicians, usually with infectious-disease and pharmacy input. Colistimethate doses are adjusted for kidney function; polymyxin B dosing is weight-based and less dependent on kidney function. International guidelines recommend loading doses and close kidney monitoring. The prescribing clinician sets and supervises dosing.
The dosing information above is aggregated from research literature and anecdotal community reports for educational purposes only. It is not a recommendation, prescription, or medical advice. Peptides are sold as research chemicals only and are not intended for human use.
Contraindications
- Known hypersensitivity to polymyxins
- Caution with other nephrotoxic or neurotoxic drugs
- Caution with neuromuscular blockers and in myasthenia gravis
No documented stacking partners for Polymyxins (Polymyxin B / Colistin) yet.
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International Consensus Guidelines for the Optimal Use of the Polymyxins: Endorsed by the American College of Clinical Pharmacy (ACCP), European Society of Clinical Microbiology and Infectious Diseases (ESCMID), Infectious Diseases Society of America (IDSA), International Society for Anti-infective Pharmacology (ISAP), Society of Critical Care Medicine (SCCM), and Society of Infectious Diseases Pharmacists (SIDP)
2019
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Colistin alone versus colistin plus meropenem for treatment of severe infections caused by carbapenem-resistant Gram-negative bacteria: an open-label, randomised controlled trial
2018
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Population pharmacokinetics of intravenous polymyxin B in critically ill patients: implications for selection of dosage regimens
2013