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#117

Polymyxin B

AntimicrobialPolymyxin B SulfateAerosporin

A cyclic lipopeptide antibiotic used as a last-resort treatment for multidrug-resistant Gram-negative bacterial infections, particularly those caused by Pseudomonas, Acinetobacter, and Klebsiella species.

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Overview

Polymyxin B is a cyclic cationic lipopeptide antibiotic originally isolated from Bacillus polymyxa in 1947. It belongs to the polymyxin family of antibiotics, which includes polymyxin E (colistin). After decades of limited use due to concerns about nephrotoxicity and neurotoxicity, polymyxin B has experienced a resurgence as a critical last-resort antibiotic for treating infections caused by multidrug-resistant (MDR) Gram-negative bacteria, particularly carbapenem-resistant organisms.

The mechanism of action involves electrostatic interaction between the positively charged peptide and the negatively charged lipid A component of bacterial lipopolysaccharide (LPS) in the outer membrane of Gram-negative bacteria. This interaction disrupts the outer membrane structure, increases permeability, and ultimately leads to cell lysis and death. Polymyxin B also has an endotoxin-neutralizing effect, binding and inactivating circulating LPS, which may provide additional benefit in sepsis.

Polymyxin B has important pharmacokinetic advantages over colistin (polymyxin E). Unlike colistin, which is administered as an inactive prodrug (colistimethate sodium), polymyxin B is given in its active form, providing more predictable plasma concentrations. This has led some infectious disease specialists to prefer polymyxin B for systemic infections, particularly bacteremia and hospital-acquired pneumonia caused by resistant organisms.

Clinical use of polymyxin B requires careful monitoring due to its nephrotoxic and neurotoxic potential. However, newer pharmacokinetic data suggest that when dosed appropriately, the rates of serious toxicity may be lower than historically reported. The drug remains an essential component of the antimicrobial armamentarium against extensively drug-resistant (XDR) and pandrug-resistant (PDR) Gram-negative pathogens.

Research Uses & Applications

  • Last-resort treatment for multidrug-resistant Gram-negative bacterial infections
  • Treatment of carbapenem-resistant Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae infections
  • Topical treatment of eye and ear infections in combination products (e.g., Neosporin)
  • Neutralization of bacterial endotoxin (LPS) in sepsis management
  • Urinary tract infections caused by resistant Gram-negative organisms
  • Selective digestive decontamination in critically ill patients

Key Research Findings

  • Pharmacokinetic studies showed polymyxin B achieves more predictable and reliable plasma concentrations than colistimethate sodium (the colistin prodrug).
  • Clinical studies demonstrated comparable efficacy to colistin for MDR Gram-negative infections with potentially lower rates of nephrotoxicity.
  • In vitro studies showed polymyxin B effectively neutralized LPS-mediated inflammatory responses at sub-antimicrobial concentrations.
  • Combination therapy studies showed synergistic bactericidal activity when polymyxin B was combined with carbapenems, rifampin, or tigecycline against resistant organisms.
  • Population pharmacokinetic modeling has improved dosing recommendations, reducing toxicity while maintaining efficacy.

Risks & Side Effects

  • Nephrotoxicity is a significant concern, occurring in 20-60% of patients depending on dosing and concomitant nephrotoxic agents.
  • Neurotoxicity can manifest as paresthesias, dizziness, weakness, and in rare cases neuromuscular blockade.
  • Requires therapeutic drug monitoring where available to optimize dosing and minimize toxicity.
  • Not effective against Gram-positive bacteria, anaerobes, or most Gram-negative cocci.
  • Risk of developing polymyxin resistance, though this remains relatively rare.

Administration

For systemic infections: intravenous administration at 1.5-2.5 mg/kg/day (15,000-25,000 units/kg/day) divided into two doses. Loading dose strategies may be employed for severe infections. Also available as topical preparations for eye, ear, and skin infections. Intrathecal or intraventricular administration for CNS infections at reduced doses. Renal function monitoring is essential during systemic therapy.

Legal Status

FDA-approved prescription antibiotic. Available in injectable form for systemic use and in various topical combination products (e.g., polymyxin B/neomycin/bacitracin in Neosporin). Restricted to prescription use. Classified as a critically important antimicrobial by the WHO.

Frequently Asked Questions

What is Polymyxin B?

A cyclic lipopeptide antibiotic used as a last-resort treatment for multidrug-resistant Gram-negative bacterial infections, particularly those caused by Pseudomonas, Acinetobacter, and Klebsiella species.

What are the main uses of Polymyxin B?

The primary research applications of Polymyxin B include: Last-resort treatment for multidrug-resistant Gram-negative bacterial infections; Treatment of carbapenem-resistant Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae infections; Topical treatment of eye and ear infections in combination products (e.g., Neosporin); Neutralization of bacterial endotoxin (LPS) in sepsis management; Urinary tract infections caused by resistant Gram-negative organisms; Selective digestive decontamination in critically ill patients.

What are the risks and side effects of Polymyxin B?

Documented risks and side effects include: Nephrotoxicity is a significant concern, occurring in 20-60% of patients depending on dosing and concomitant nephrotoxic agents.; Neurotoxicity can manifest as paresthesias, dizziness, weakness, and in rare cases neuromuscular blockade.; Requires therapeutic drug monitoring where available to optimize dosing and minimize toxicity.; Not effective against Gram-positive bacteria, anaerobes, or most Gram-negative cocci.; Risk of developing polymyxin resistance, though this remains relatively rare.. Always consult a healthcare professional before considering any peptide.

Is Polymyxin B legal?

FDA-approved prescription antibiotic. Available in injectable form for systemic use and in various topical combination products (e.g., polymyxin B/neomycin/bacitracin in Neosporin). Restricted to prescription use. Classified as a critically important antimicrobial by the WHO.

How is Polymyxin B administered?

For systemic infections: intravenous administration at 1.5-2.5 mg/kg/day (15,000-25,000 units/kg/day) divided into two doses. Loading dose strategies may be employed for severe infections. Also available as topical preparations for eye, ear, and skin infections. Intrathecal or intraventricular administration for CNS infections at reduced doses. Renal function monitoring is essential during systemic therapy.

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The information on this page is for educational and informational purposes only. It is not intended as medical advice. Always consult a qualified healthcare professional before considering any peptide or supplement. 50 Best Limited does not endorse, recommend, or promote the use of any peptide for self-administration. Read our full disclaimer.

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