How Does Polymyxin B Work? Mechanism of Action, Per the Research

Polymyxin B is an antibacterial agent that has been studied for decades and is described in the pharmacology literature as a polycationic cyclic lipopeptide with activity against Gram-negative bacteria. A 2010 review of polymyxins and their novel derivatives in Current Opinion in Microbiology summarised the structural features of this class and the medicinal-chemistry work aimed at producing derivatives with altered properties (PMID 20869908). This page describes what published research reports about how the molecule interacts with bacterial membranes, what parts of that mechanism are well established, and what remains proposed or contested. For a broader overview of the compound, see the hub page at /learn/polymyxin-b/.

This page is for educational purposes only and is not medical advice; consult a licensed physician about any medical question, medication or clinical decision. No dosing information, protocols or usage instructions appear here, and nothing below should be read as a recommendation.

The Target: Lipopolysaccharide in the Gram-Negative Outer Membrane

The starting point for every mechanistic account of polymyxin B is the outer membrane of Gram-negative bacteria, whose outer leaflet is densely packed with lipopolysaccharide (LPS). The 2010 review in Current Opinion in Microbiology described the polymyxins as cationic lipopeptides whose activity is tied to interaction with this LPS-rich envelope and discussed how derivative programmes have tried to modify that interaction (PMID 20869908). A 2016 review in Cold Spring Harbor Perspectives in Medicine likewise framed the canonical mechanism around the LPS target before turning to alternative mechanisms and resistance (PMID 27503996).

The key chemistry is electrostatic. Polymyxin B carries multiple positively charged diaminobutyric acid residues, while the lipid A anchor of LPS carries negative charges normally bridged by divalent cations such as magnesium and calcium. The literature describes the antibiotic displacing those cations and inserting its fatty acyl tail into the lipid bilayer — a two-part interaction combining charge attraction and hydrophobic insertion. That the molecule binds LPS and lipid A is the least disputed element of its pharmacology; it is also the property exploited in non-antibiotic applications discussed below (PMID 25043934).

Self-Promoted Uptake

Because the outer membrane normally excludes large or hydrophobic molecules, disruption of LPS packing increases permeability. Reviews of the class describe this as "self-promoted uptake": the molecule degrades the barrier that would otherwise limit its own access, allowing more of it — and in laboratory work, other agents — to reach the inner membrane. The 2016 Cold Spring Harbor Perspectives in Medicine review placed outer-membrane permeabilisation at the centre of the established model while noting that it does not by itself explain every observation about polymyxin killing (PMID 27503996).

What the 2025 Nature Microbiology Work Added

A 2025 study published in Nature Microbiology addressed a long-standing gap: whether binding and physical disruption alone are sufficient to kill, or whether bacterial physiology participates. The study reported that polymyxin B lethality required energy-dependent outer membrane disruption (PMID 41023239). In other words, researchers found that the killing step was not a purely passive detergent-like event; it depended on processes in the cell that consume energy.

This finding matters for how the mechanism is taught. A strictly physicochemical model predicts that killing should proceed in metabolically inert cells, since soap-like disruption needs no cooperation from the target. The 2025 report instead tied lethality to an energy-dependent step at the outer membrane (PMID 41023239). Readers should note this was bacterial laboratory work, not a clinical trial, and that mechanistic findings in cultured bacteria do not translate directly into statements about outcomes in people.

Established Mechanism Versus Proposed Mechanism

It is useful to separate what the literature treats as settled from what it treats as hypothesis.

The 2016 review was explicitly titled around alternative mechanisms of action and resistance, signalling that the field had moved past a single-mechanism account (PMID 27503996). Where this page does not list a specific alternative pathway, it is because the verified source set does not support naming one; readers interested in the detail can consult that review directly.

Endotoxin Binding, TLR4 and the Non-Antibiotic Line of Research

Because LPS is also the ligand that activates Toll-like receptor 4 (TLR4) on host immune cells, the same binding chemistry has been investigated for purposes other than killing bacteria. A 2014 paper in Critical Care offered a mechanistic perspective on polymyxin B hemoperfusion, in which the molecule is immobilised on a cartridge so that circulating endotoxin can be adsorbed rather than delivered systemically as a drug (PMID 25043934). The researchers framed the rationale around the compound's affinity for endotoxin; the paper was a mechanistic discussion rather than an outcome trial, and this page makes no claim about patient outcomes.

More recently, a 2026 paper in Advanced Materials described an LPS-binding hydrogel developed for TLR4-mediated modulation of microbiota–immune interactions, extending the same binding principle into a materials-science format (PMID 41255157). That work was preclinical materials research. Together these two papers illustrate a recurring theme: the LPS-binding property is being explored both as an antibacterial mechanism and as a way to sequester endotoxin and dampen TLR4 signalling (PMID 25043934, PMID 41255157).

How Bacteria Defeat the Mechanism: Resistance

Resistance mechanisms are informative because they are, in effect, the mechanism run in reverse. A 2018 review in Recent Patents on Anti-Infective Drug Discovery covered polymyxin resistance from intrinsic resistance through to mobile mcr genes (PMID 30474535). The general principle described across the resistance literature is that bacteria reduce the negative charge of lipid A, which weakens the electrostatic attraction the antibiotic depends on. Intrinsically resistant species achieve this constitutively; inducible systems do it in response to environmental signals; and plasmid-borne mcr determinants, reviewed in that same paper, made the trait transferable between organisms (PMID 30474535).

The 2016 Cold Spring Harbor Perspectives in Medicine review paired its discussion of alternative mechanisms with resistance for the same reason — if killing involves more than one pathway, resistance may involve more than charge modification alone (PMID 27503996). The 2010 review of novel derivatives described efforts to design analogues around these constraints (PMID 20869908).

Pharmacokinetics: What Animal Studies Describe

Mechanism at the membrane is separate from what happens to the molecule in a body. A 2019 chapter in Advances in Experimental Medicine and Biology reviewed the pharmacokinetics of polymyxins in animals, collecting absorption, distribution and elimination data from animal models (PMID 31364073). That review was explicitly animal pharmacokinetics; this page does not extrapolate from it to human exposure, and no quantities are reproduced here because dosing information is outside this page's scope.

Mechanism-Linked Adverse Effects: What Studies Report

The same chemistry that makes polymyxin B bind membranes has been linked in the literature to off-target effects, which is why mechanism and toxicity are usually discussed together.

Kidney

A 2019 paper in Antibiotics addressed polymyxin acute kidney injury, discussing dosing and other strategies investigated to reduce toxicity (PMID 30875778). The researchers framed nephrotoxicity as the dose-limiting problem for the class; no specific regimen is reproduced here, and the paper should be read in full by clinicians rather than summarised numerically on an educational page.

Skin and Pigmentation

A 2017 case report in the Journal of Clinical and Diagnostic Research described polymyxin B-induced diffuse cutaneous hyperpigmentation (PMID 28384882). Case reports describe single individuals and cannot establish frequency. Separately, a 2021 paper in the European Journal of Dermatology examined whether contact pemphigus exists as an entity, in a literature where topical agents including polymyxin-containing preparations have been discussed as triggers (PMID 33337331).

Protein Aggregation In Vitro

A 2021 study in Biophysical Chemistry reported that polymyxin B accelerated α-synuclein aggregation (PMID 34118773). This was in-vitro biophysics using purified protein, not an animal or human study, and the researchers' finding describes a molecular interaction rather than a clinical event. It is included because it illustrates that a strongly cationic amphipathic peptide can influence protein behaviour beyond bacterial membranes.

Where Polymyxin B Appears Incidentally in Research

Polymyxin B is widely used as an additive in culture and tissue-preservation media, so it sometimes appears in papers that are not about the drug at all. A 2024 study in Current Eye Research examined whether human breast milk enhanced cellular proliferation in corneal wound healing, a context in which antibiotic-containing media are routine (PMID 38979814). Readers scanning literature searches should distinguish papers studying the compound from papers merely using it as a reagent.

What the Mechanism Literature Does Not Establish

• It does not establish outcomes. Mechanistic work in bacteria, such as the 2025 energy-dependence finding, describes molecular events, not patient results (PMID 41023239).
• It does not settle the alternative-mechanism question. The 2016 review presented alternatives as an active area rather than a resolved one (PMID 27503996).
• It does not translate animal pharmacokinetics to humans. The 2019 review covered animal data as animal data (PMID 31364073).
• It does not quantify adverse-event risk for an individual. Case reports describe individuals (PMID 28384882).

In summary, the published account of how polymyxin B works centres on cationic binding to lipid A, displacement of stabilising divalent cations, insertion into and permeabilisation of the outer membrane, and — per 2025 work — an energy-dependent step required for lethality (PMID 41023239). Resistance arises largely by reducing the negative charge the molecule targets (PMID 30474535), and the LPS-binding property has been explored separately for endotoxin sequestration and TLR4-directed research (PMID 25043934, PMID 41255157). Again, this page is educational only and is not medical advice; medication questions belong with a licensed physician.

References

• Polymyxin B lethality requires energy-dependent outer membrane disruption (Nature Microbiology, 2025)
• LPS-Binding Hydrogel for TLR4-Mediated Microbiota-Immune Modulation (Advanced Materials, 2026)
• Pharmacokinetics of Polymyxins in Animals (Advances in Experimental Medicine and Biology, 2019)
• Contact pemphigus: does it exist? (European Journal of Dermatology, 2021)
• Polymyxin B accelerates the α-synuclein aggregation (Biophysical Chemistry, 2021)
• Polymyxin B hemoperfusion: a mechanistic perspective (Critical Care, 2014)
• Polymyxin: Alternative Mechanisms of Action and Resistance (Cold Spring Harbor Perspectives in Medicine, 2016)
• Polymyxins and their novel derivatives (Current Opinion in Microbiology, 2010)
• Polymyxin Resistance Mechanisms: From Intrinsic Resistance to Mcr Genes (Recent Patents on Anti-Infective Drug Discovery, 2018)
• Polymyxin Acute Kidney Injury: Dosing and Other Strategies to Reduce Toxicity (Antibiotics, 2019)
• Polymyxin B-Induced Diffuse Cutaneous Hyperpigmentation (Journal of Clinical and Diagnostic Research, 2017)
• Human Breast Milk Enhances Cellular Proliferation in Cornea Wound Healing (Current Eye Research, 2024)