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approvedImmune & Inflammation

Polymyxin B

Also known as: Polymyxin B Sulfate, PMB, Aerosporin, Poly-Rx

Polymyxin B is a cyclic lipopeptide antibiotic originally isolated from Bacillus polymyxa in 1947. It is one of the last-resort antibiotics for multidrug-resistant (MDR) gram-negative infections caused by Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae. Despite significant nephrotoxicity concerns, it has returned to frontline clinical use due to the global crisis of carbapenem-resistant gram-negative infections.

3 cited references·6 researched benefits

Quick Answer

Polymyxin B is a cyclic lipopeptide antibiotic approved as a last-resort treatment for multidrug-resistant gram-negative bacterial infections including Pseudomonas aeruginosa and Acinetobacter baumannii. It kills bacteria by binding to lipopolysaccharide (LPS) in the outer membrane, causing membrane disruption and cell death. Despite dose-limiting nephrotoxicity, polymyxin B has experienced a clinical resurgence due to the global spread of carbapenem-resistant gram-negative pathogens with no other treatment options.

Key Facts

Mechanism
Polymyxin B exerts bactericidal activity through electrostatic interaction between its positively charged diaminobutyric acid residues and the negatively charged phosphate groups of lipid A in gram-negative bacterial lipopolysaccharide (LPS). This initial binding displaces divalent cations (Ca²⁺ and Mg²⁺) that stabilize the outer membrane, causing destabilization. The fatty acid tail of polymyxin B then inserts into the hydrophobic interior of the outer membrane, disrupting its integrity. This "self-promoted uptake" allows polymyxin B to reach and permeabilize the inner cytoplasmic membrane, leading to leakage of cellular contents and rapid cell death. It also neutralizes circulating endotoxin (LPS), providing an anti-endotoxin effect.
Research Status
approved
Half-Life
~6 hours
Molecular Formula
C₅₆H₉₈N₁₆O₁₃
Primary Use
Immune & Inflammation
Table of Contents

Benefits

  • Effective last-resort treatment for carbapenem-resistant gram-negative infections (CRE, CRAB, MDR Pseudomonas)strong
  • Rapid bactericidal activity through membrane disruption mechanismstrong
  • Direct endotoxin (LPS) neutralization reduces sepsis-associated inflammatory cascademoderate
  • Synergistic activity when combined with carbapenems, rifampin, or tigecycline against MDR organismsmoderate
  • Topical ophthalmic and otic formulations for localized infections with minimal systemic toxicitystrong
  • Polymyxin B hemoperfusion cartridges used in Japan and Europe for endotoxin removal in sepsispreliminary

Dosage Protocols

RouteDosage RangeFrequencyNotes
Intravenous1.5–2.5 mg/kg/day (15,000–25,000 units/kg/day)Divided into 2 doses every 12 hoursStandard systemic dosing for MDR gram-negative infections; requires renal function monitoring
Intrathecal/Intraventricular5 mg (50,000 units) dailyDaily for 3-4 days, then every other dayFor CNS infections with MDR gram-negative organisms; meningitis or ventriculitis
Topical (ophthalmic/otic)10,000 units/mL solution3-6 times dailyAvailable in combination products (e.g., with neomycin and hydrocortisone) for eye and ear infections

Medical disclaimer

Dosage information is provided for educational reference only. Always follow your prescriber's instructions and consult a qualified healthcare provider before starting any peptide protocol.

Side Effects

  • Nephrotoxicity (acute kidney injury in 20-60% of treated patients)serious
  • Neurotoxicity including dizziness, paresthesias, and visual disturbancesserious
  • Infusion-related reactions including flushing, pruritus, and chest tightnesscommon
  • Skin hyperpigmentation with prolonged intravenous usecommon
  • Respiratory paralysis at very high doses (rare with appropriate dosing)serious

Frequently Asked Questions

What is the difference between polymyxin B and colistin?
Polymyxin B and colistin (polymyxin E) are both cyclic lipopeptide antibiotics with similar mechanisms, but differ in important pharmacokinetic properties. Polymyxin B is administered as the active drug and achieves more predictable plasma concentrations. Colistin is given as the inactive prodrug colistimethate sodium (CMS) that requires conversion to active colistin, resulting in variable and unpredictable plasma levels. Recent evidence suggests polymyxin B may be preferred for systemic infections due to more reliable pharmacokinetics, while colistin via nebulization may be preferred for pulmonary infections.
Why are polymyxins called "last-resort" antibiotics?
Polymyxins are reserved for infections caused by multidrug-resistant gram-negative bacteria that are resistant to all other available antibiotics, including carbapenems (the previous "last line of defense"). Due to significant toxicity, particularly nephrotoxicity, they are only used when no safer alternative exists. The increasing global prevalence of carbapenem-resistant Enterobacteriaceae (CRE) and extensively drug-resistant (XDR) Acinetobacter and Pseudomonas has forced polymyxins back into clinical prominence despite their toxicity profile.
How is polymyxin B-associated kidney damage monitored?
Patients receiving systemic polymyxin B require daily monitoring of serum creatinine, blood urea nitrogen (BUN), and urine output. Therapeutic drug monitoring (TDM) of polymyxin B plasma concentrations is increasingly recommended to optimize dosing. The target AUC/MIC is 50-100 to balance efficacy against nephrotoxicity risk. Concurrent nephrotoxic agents should be avoided when possible, and hydration status should be maintained. Acute kidney injury typically appears within the first week of therapy and is usually reversible upon discontinuation.

References

  1. 1
    Polymyxins: pharmacology, pharmacokinetics, pharmacodynamics, and clinical applications(2015)PubMed ↗
  2. 2
    Polymyxin B versus colistin for the treatment of multidrug-resistant infections: a systematic review(2019)PubMed ↗
  3. 3
    International consensus guidelines for the optimal use of the polymyxins(2019)PubMed ↗

Latest Research

Last updated: 2026-02-19