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Polymyxins were first discovered in 1947 but were largely superseded by less nephrotoxic antibiotics in the 1970s.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.
Side effects
Side effects vary by individual. This is not an exhaustive list. Report unusual symptoms to a healthcare professional.
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.
Where to get it
Prescription required
Polymyxin B is a prescription medication. Consult your healthcare provider or a licensed telehealth platform for access.