Quick summary
Polymyxin B is a cyclic lipopeptide antibiotic and last-resort treatment for multidrug-resistant gram-negative infections. It disrupts bacterial outer membranes and neutralizes endotoxin, but nephrotoxicity affects 30-60% of patients.
Overview
Polymyxin B is a cyclic lipopeptide antibiotic produced by Paenibacillus polymyxa, used as a last-resort treatment for multidrug-resistant gram-negative infections. It comprises a cyclic heptapeptide ring with an exocyclic tripeptide tail linked to a fatty acid. FDA-approved for systemic and topical use, polymyxin B is active against Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacteriaceae including carbapenem-resistant strains.
Mechanism of action
Polymyxin B targets the bacterial outer membrane by electrostatically binding the phosphate groups of lipid A in lipopolysaccharide (LPS), displacing stabilizing divalent cations (Ca2+, Mg2+). This disrupts outer membrane integrity, increases permeability, and allows entry of the hydrophobic fatty acid tail into the inner membrane, where it causes further disruption, ion leakage, and loss of membrane potential. The bactericidal effect is rapid at higher concentrations. Polymyxin B also directly neutralizes LPS (endotoxin), which may attenuate sepsis-associated inflammatory cascades.
Dosing protocols
| Purpose | Route | Dosage | Frequency | Notes |
|---|---|---|---|---|
| severe MDR gram-negative infection | intravenous | 15000–25000 IU/kg/day | divided every 12 hours | Maximum 2 million IU/day; loading dose of 25,000 IU/kg may be used; dose-adjust for renal impairment |
| topical wound / ophthalmic | topical | 10000–10000 IU/mL | as directed per formulation | Combination formulations (Neosporin): applied 1–3x daily to affected area |
| intramuscular (less common) | intramuscular | 25000–30000 IU/kg/day | divided every 4–6 hours | IM route is painful and less preferred than IV; use only when IV access not available |
Dosing information is for educational purposes only. Consult a qualified healthcare professional before using any peptide.
Research summary
Polymyxins were first discovered in 1947 but were largely superseded by less nephrotoxic antibiotics in the 1970s. The emergence of carbapenem-resistant gram-negative infections has driven their resurgence since the 2000s. Polymyxin B and colistin (polymyxin E) are now critical last-resort agents for XDR Acinetobacter and Pseudomonas. Nephrotoxicity (30–60% incidence) and neurotoxicity remain major dose-limiting concerns. Pharmacokinetic/pharmacodynamic optimization studies show that higher daily doses improve bactericidal outcomes. Inhaled polymyxin B is studied for VAP prevention. Resistance via lipid A modification (MCR-1) is emerging globally.[1][2][3][4][5]
Evidence grading
Each claimed benefit is graded by the strength of available evidence. Grades reflect study quality, not effect size.
Strong = multiple RCTs · Moderate = limited trials or observational · Preliminary = animal or in vitro only · Insufficient = anecdotal or no published data
Side effects
Side effects vary by individual. This is not an exhaustive list. Report unusual symptoms to a healthcare professional.
Common stacks
Peptides commonly paired with Polymyxin B for synergistic effects.
Legal status
FDA-approved for serious gram-negative infections (IV, IM) and as a topical component in combination products (e.g., Neosporin). IV use is restricted to severe infections where safer alternatives are not available, due to nephrotoxicity and neurotoxicity risks.
Sourcing & access
Prescription required
Polymyxin B is an FDA-approved prescription medication available through licensed healthcare providers, telehealth platforms, and 503A/503B compounding pharmacies.
Frequently asked questions
Polymyxin B is a cyclic lipopeptide antibiotic produced by Paenibacillus polymyxa. It is FDA-approved for serious gram-negative infections and is used as a last-resort treatment for multidrug-resistant organisms including carbapenem-resistant Acinetobacter baumannii and Pseudomonas aeruginosa.
Polymyxin B binds the lipid A component of LPS in gram-negative bacterial outer membranes, displacing stabilizing divalent cations and disrupting membrane integrity. Its hydrophobic fatty acid tail penetrates the inner membrane, causing ion leakage and rapid bactericidal effects. It also directly neutralizes endotoxin.
Nephrotoxicity occurs in 30-60% of patients receiving systemic Polymyxin B, and neurotoxicity (paresthesias, dizziness, ataxia) is also common. Rare respiratory muscle paralysis can occur. These serious side effects limit its use to infections where no safer alternatives are available.
Originally discovered in 1947 and largely superseded by less toxic antibiotics, polymyxins have resurged since the 2000s due to the global emergence of carbapenem-resistant gram-negative infections. Polymyxin B and colistin are now critical last-resort agents, though resistance via MCR-1 lipid A modification is emerging.
Both are polymyxin antibiotics with similar mechanisms. Polymyxin B is administered as the active drug, while colistin (polymyxin E) is given as the inactive prodrug colistimethate. Polymyxin B has more predictable pharmacokinetics and is increasingly preferred for systemic infections.
Research references
- Resurgence of Polymyxin B for MDR/XDR Gram-Negative Infections: An Overview of Current EvidencePubMed
- Polymyxin B Nephrotoxicity: From Organ to Cell DamagePubMed
- Polymyxin B Clinical Outcomes: A Prospective Study of Patients Undergoing Intravenous TreatmentPubMed
- Polymyxins, the Last-Resort Antibiotics: Mode of Action, Resistance Emergence, and Potential SolutionsPubMed
- Polymyxin B for the Treatment of Multidrug-Resistant Pathogens: A Critical ReviewPubMed