How is polymyxin B different from colistin?

Both are polymyxins; colistin is polymyxin E. Polymyxin B is given as the active drug, whereas colistin is given as an inactive prodrug (colistimethate), and consensus guidelines often prefer polymyxin B for its more predictable pharmacokinetics.

What is the main risk of polymyxin B?

Nephrotoxicity (kidney injury) is the dose-limiting toxicity, and neurotoxicity can also occur. Acute kidney injury was common in prospective cohorts and linked to higher mortality.

What infections is it used for?

It is used as a last-resort agent against multidrug-resistant and carbapenem-resistant Gram-negative bacteria when other antibiotics are ineffective, and topically in some skin and eye preparations.

Can I use polymyxin B on my own?

No. Systemic polymyxin B is a hospital-administered, specialist-supervised antibiotic requiring careful dosing and kidney monitoring. This page is educational context, not medical advice.

EMA-approved

Polymyxin B — Complete Research Guide (2026)

Last updated 2026-06-30

TL;DR

Polymyxin B is a peptide catalogued under Cyclic & Antimicrobial (Polymyxin (cyclic lipopeptide)). It is described as: LPS/outer membrane. Documented context: Multi-resistant Gram-negative infections. Neutral reference entry; EU status: EU-approved prescription medicine.

What is Polymyxin B?

Polymyxin B is a cyclic lipopeptide antibiotic of the polymyxin class, closely related to colistin (which is polymyxin E), and is active against Gram-negative bacteria. It is an FDA-approved prescription drug used topically and, as a last-resort intravenous agent, against multidrug-resistant and carbapenem-resistant Gram-negative infections.

Its systemic evidence base rests largely on observational cohorts, pharmacokinetic work, and multi-society consensus guidelines rather than large modern randomized controlled trials. Clinical use is constrained by dose-dependent nephrotoxicity and neurotoxicity, so it is reserved for serious infections when better-tolerated options are unavailable.

How does Polymyxin B work?

Polymyxin B binds the lipid A moiety of lipopolysaccharide in the Gram-negative outer membrane, displacing divalent cations that stabilize it.

This disrupts membrane integrity and causes leakage of intracellular contents and bacterial cell death.

What does the research say about Polymyxin B?

Polymyxin B is used intravenously as a last-resort treatment for multidrug-resistant Gram-negative infections, and an evaluation of current evidence supports this clinical role despite limited trial-quality data. ^[1]
International multi-society consensus guidelines recommend polymyxin B over colistin for most systemic infections because of its more predictable pharmacokinetics. ^[2]
As a last-line polymyxin, it retains bactericidal activity against many carbapenem-resistant Gram-negative organisms that resist other antibiotic classes. ^[3]

Clinical research & studies

The references below are the primary sources cited throughout this guide. Each links directly to PubMed or the regulator. Where evidence is preclinical (animal or in-vitro), that is stated rather than implied.

[1] Clinical use of intravenous polymyxin B for the treatment of patients with multidrug-resistant Gram-negative bacterial infections: An evaluation of the current evidence — Falagas ME et al., Journal of Global Antimicrobial Resistance 2021. (Evidence review (human clinical use))
[2] International Consensus Guidelines for the Optimal Use of the Polymyxins: Endorsed by the American College of Clinical Pharmacy (ACCP), European Society of Clinical Microbiology and Infectious Diseases (ESCMID), Infectious Diseases Society of America (IDSA), International Society for Anti-infective Pharmacology (ISAP), Society of Critical Care Medicine (SCCM), and Society of Infectious Diseases Pharmacists (SIDP) — Tsuji BT et al., Pharmacotherapy 2019. (Consensus guideline)
[3] Rescuing the Last-Line Polymyxins: Achievements and Challenges — Nang SC et al., Pharmacological Reviews 2021. (Review)
[4] Risk factors for acute kidney injury (AKI) in patients treated with polymyxin B and influence of AKI on mortality: a multicentre prospective cohort study — Rigatto MH et al., Journal of Antimicrobial Chemotherapy 2015. (Prospective cohort)
[5] Adverse reactions associated with systemic polymyxin therapy — Justo JA et al., Pharmacotherapy 2015. (Narrative review (human adverse events))
[6] Polymyxins: Antibacterial Activity, Susceptibility Testing, and Resistance Mechanisms Encoded by Plasmids or Chromosomes — Poirel L et al., Clinical Microbiology Reviews 2017. (Review)

Dosing context

This is not medical advice or a usage recommendation. Dosing figures are reported research context only, cited from the published literature.

Systemic polymyxin B is administered intravenously with weight-based dosing, and consensus guidelines describe a loading dose followed by maintenance dosing, ideally with therapeutic drug monitoring where available.

This is context only and not a usage recommendation; dosing must be individualized by clinicians.

Side effects & safety profile

Nephrotoxicity is the dose-limiting toxicity: in a multicentre prospective cohort acute kidney injury occurred in a substantial share of polymyxin B-treated patients and was associated with mortality.

Neurotoxicity (paresthesias, dizziness, and rarely neuromuscular blockade) is also reported.

Because of these risks it should only be used under specialist supervision for serious resistant infections.

Stacking & combinations

In resistant infections polymyxin B is frequently combined with a second active antibiotic to broaden coverage and limit resistance, but the combination is a clinical decision made case by case.

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Frequently asked questions

Yes. Polymyxin B is an FDA-approved prescription antibiotic, used both topically and intravenously, though its systemic use is reserved for serious multidrug-resistant Gram-negative infections.

References

[1] Clinical use of intravenous polymyxin B for the treatment of patients with multidrug-resistant Gram-negative bacterial infections: An evaluation of the current evidence — Falagas ME et al., Journal of Global Antimicrobial Resistance 2021. PMID: 33486122. View sourceStudy: Evidence review (human clinical use)Reviewed current clinical evidence supporting intravenous polymyxin B for multidrug-resistant Gram-negative infections while noting limited high-quality trial data.
[2] International Consensus Guidelines for the Optimal Use of the Polymyxins: Endorsed by the American College of Clinical Pharmacy (ACCP), European Society of Clinical Microbiology and Infectious Diseases (ESCMID), Infectious Diseases Society of America (IDSA), International Society for Anti-infective Pharmacology (ISAP), Society of Critical Care Medicine (SCCM), and Society of Infectious Diseases Pharmacists (SIDP) — Tsuji BT et al., Pharmacotherapy 2019. PMID: 30710469. View sourceStudy: Consensus guidelineMulti-society guidelines on optimal polymyxin dosing that favor polymyxin B for most systemic infections.
[3] Rescuing the Last-Line Polymyxins: Achievements and Challenges — Nang SC et al., Pharmacological Reviews 2021. PMID: 33627412. View sourceStudy: ReviewComprehensive review of polymyxins as last-line agents against multidrug-resistant Gram-negative bacteria, covering activity, resistance, and toxicity.
[4] Risk factors for acute kidney injury (AKI) in patients treated with polymyxin B and influence of AKI on mortality: a multicentre prospective cohort study — Rigatto MH et al., Journal of Antimicrobial Chemotherapy 2015. PMID: 25604744. View sourceStudy: Prospective cohortAcute kidney injury was common in polymyxin B-treated patients and was associated with increased mortality.
[5] Adverse reactions associated with systemic polymyxin therapy — Justo JA et al., Pharmacotherapy 2015. PMID: 25266910. View sourceStudy: Narrative review (human adverse events)Reviewed adverse reactions to systemic polymyxins, most importantly nephrotoxicity and neurotoxicity.
[6] Polymyxins: Antibacterial Activity, Susceptibility Testing, and Resistance Mechanisms Encoded by Plasmids or Chromosomes — Poirel L et al., Clinical Microbiology Reviews 2017. PMID: 28275006. View sourceStudy: ReviewReviewed polymyxin antibacterial activity, susceptibility testing, and plasmid- and chromosome-encoded resistance mechanisms.

This article is for educational and research purposes only. Peptides discussed here are not approved for human consumption by the FDA, EMA, or equivalent regulators outside of specific clinical contexts. Always consult a licensed medical professional before any therapeutic use.