What Is Polymyxin Used For? Approved Uses, Per the Label

Polymyxin is a prescription medicine. In the United States, polymyxin B sulfate is an approved prescription antibacterial drug, supplied both as a sterile powder for injection and as an ingredient in combination topical, ophthalmic and otic products. The closely related member of the same family, polymyxin E, is marketed in the United States as colistimethate sodium, also a prescription product. This page describes what the approved labeling covers, how those indications came to exist, and what the published literature reported about polymyxin activity and outcomes. This page is for educational purposes only and is not medical advice; consult a licensed physician or prescribing clinician about any individual medical question.

The short answer

Polymyxins are used as antibacterial agents directed at Gram-negative bacteria. Approved labeling for the injectable product centres on acute and serious infections caused by susceptible Gram-negative organisms, with an explicit framing that the drug is reserved for situations in which less potentially toxic agents are ineffective or contraindicated. Combination products containing polymyxin B are approved for localised use on skin, in the eye and in the external ear canal, depending on the specific product. A 2021 review in Pharmacological Reviews described the polymyxins as last-line agents that returned to clinical use because of multidrug-resistant Gram-negative pathogens (PMID 33627412).

What the polymyxin family includes

Two members of the family reached clinical use: polymyxin B and polymyxin E (colistin, administered as the prodrug colistimethate sodium). Both are cyclic lipopeptide antibacterials that act at the Gram-negative outer membrane. A 2019 chapter summarising in vitro pharmacodynamics and animal pharmacokinetic and pharmacodynamic work described how exposure measures relate to bacterial killing and to regrowth of resistant subpopulations in laboratory and animal models (PMID 31364074). Background on the chemistry and mechanism of this drug class is covered on the polymyxin learn page.

Approved uses, by product form

Approved indication wording differs between manufacturers and between the many generic versions of these products, and the verified literature cited on this page does not supply label revision years for any individual product. The categories below describe what United States prescribing information for polymyxin-containing products covers. The current FDA-approved labeling for a specific product, including its revision date, is the authoritative source for that product.

Systemic polymyxin B

The injectable product carries the narrowest and most heavily qualified indication language. Labeling frames the drug as appropriate for acute infections caused by susceptible strains of Pseudomonas aeruginosa, and for serious infections caused by susceptible Gram-negative organisms when less potentially toxic agents are ineffective or contraindicated. That reservation language reflects the toxicity profile that dominated the class for decades and that a 2021 review described as the principal barrier to wider systemic use (PMID 33627412).

Localised combination products

Most polymyxin B exposure in everyday medicine occurs through fixed combinations with bacitracin, neomycin, trimethoprim or a corticosteroid, formulated for the skin, eye or ear. These products carry their own approved indications specific to the site and the combination, and those indications are not interchangeable with the injectable product's indications.

Colistimethate sodium

Colistimethate sodium is the approved parenteral form of polymyxin E in the United States. Its labeling covers acute and chronic infections due to susceptible strains of certain Gram-negative bacilli. Because colistimethate is an inactive prodrug converted to colistin in the body, dosing conventions and exposure measures differ from polymyxin B, a distinction examined in preclinical pharmacokinetic and pharmacodynamic work summarised in 2019 (PMID 31364074).

Regulatory history of the indications

The polymyxins were introduced into clinical medicine in the late 1940s and 1950s, before modern requirements for adequate and well-controlled efficacy trials were written into United States law by the 1962 Drug Amendments. As a result, the labeled indications for polymyxin B for injection were not built on named pivotal randomised controlled trials in the way that indications for a contemporary antibacterial would be. The verified literature set cited on this page contains no pivotal registration trial for the original systemic indications, and none should be inferred.

Systemic polymyxin use fell away during the 1970s and 1980s as better tolerated agents became available, then returned after carbapenem-resistant Gram-negative pathogens spread internationally. A 2021 review traced that revival and described the scientific gaps that accompanied it, including the limited quality of the older dosing and efficacy record (PMID 33627412). Much of the modern evidence base therefore consists of observational cohorts, pharmacokinetic and pharmacodynamic modelling, and meta-analyses rather than registration trials.

What the clinical literature reported

A 2019 meta-analysis of polymyxin use in patients pooled published clinical experience with the class and examined outcomes across the included studies (PMID 31364077). A 2023 study in Infection and Drug Resistance examined the efficacy of polymyxin B and the factors influencing it in high-level carbapenem-resistant Klebsiella pneumoniae infections, and researchers reported on clinical and microbiological outcomes in that population (PMID 37396067). These reports describe how the drug performed in practice; they do not expand the approved indication wording, which is set by the labeling itself.

Combination approaches have been studied extensively because polymyxin monotherapy can allow regrowth of less susceptible bacterial subpopulations. A 2017 review in The Journal of Infection discussed the clinical translation of polymyxin-based combination therapy and set out the facts, challenges and open questions around moving laboratory synergy into patient care (PMID 27998750). Laboratory and animal pharmacodynamic work in the same period examined the exposure patterns associated with bacterial killing and with emergence of resistance (PMID 31364074).

Adverse Events in Polymyxin Studies: What Studies Report

Toxicity is central to why the injectable labeling reserves polymyxin for situations in which less potentially toxic agents are unsuitable. The 2021 Pharmacological Reviews article described nephrotoxicity and neurotoxicity as the dose-limiting problems that historically constrained systemic polymyxin therapy and that continue to shape optimisation efforts (PMID 33627412). The 2019 meta-analysis of polymyxin use in patients examined outcomes reported across published patient series, including safety outcomes attributed to the class (PMID 31364077). The 2023 carbapenem-resistant Klebsiella pneumoniae study likewise reported on factors influencing outcomes with polymyxin B in that setting (PMID 37396067). No numeric rates are reproduced here, because specific incidence figures depend on the population, the formulation and the exposure achieved, all of which a prescribing clinician assesses individually. Full warnings, contraindications and monitoring requirements appear in the FDA-approved labeling for each product.

Research directions that are not approved uses

The following are not approved uses in the United States. Polymyxin B hemoperfusion, a device-based extracorporeal approach to endotoxin removal in septic shock, was evaluated in the EUPHRATES and TIGRIS programmes, and a 2025 narrative review in the Journal of Intensive Care summarised the combined evidence from both trials (PMID 41291942), following earlier commentary on the transition between those studies (PMID 31131109). Separately, laboratory groups have tested agents intended to restore or amplify polymyxin activity, including adjuvants screened against polymyxin B- and carbapenem-resistant Gram-negative bacteria (PMID 39258398), hyperforin as a potentiator acting through membrane disruption and oxidative stress in a 2025 report (PMID 41222309), and gallium nitrate tested against polymyxin-resistant Klebsiella pneumoniae strains (PMID 34775292). Work on next-generation analogues has also continued, summarised in a 2019 chapter on the discovery of novel polymyxin-like antibiotics (PMID 31364086). None of this preclinical or device work changes the approved indications of marketed polymyxin products.

How to read the label versus the literature

• Labeled indications define what a product is approved to treat and are set by the FDA-approved prescribing information for that specific product and manufacturer.
• Published studies describe how a drug performed in defined populations and models. A 2019 meta-analysis of polymyxin use in patients is an example of pooled clinical reporting rather than an indication (PMID 31364077).
• Preclinical work, such as the animal pharmacokinetic and pharmacodynamic studies summarised in 2019, informs how a drug might be optimised but does not establish clinical indications (PMID 31364074).
• Susceptibility matters. Every polymyxin indication category is qualified by the organism being susceptible, which is determined by microbiology testing rather than by a general label statement.

Questions that belong with a prescribing clinician

Whether a polymyxin product is appropriate in a given infection, which formulation applies, how susceptibility testing is interpreted, how kidney function and other medicines change the risk picture, and how long therapy continues are all decisions made by a treating clinician with access to the full clinical record. This page does not provide dosing information and does not evaluate individual situations. Anyone with a question about polymyxin therapy should direct it to a licensed physician or pharmacist, who can consult the current approved labeling for the exact product in question.

References

• Rescuing the Last-Line Polymyxins: Achievements and Challenges (Pharmacological Reviews, 2021)
• Meta-analysis of Polymyxin Use in Patients (Advances in Experimental Medicine and Biology, 2019)
• In vitro Pharmacodynamics and PK/PD in Animals (Advances in Experimental Medicine and Biology, 2019)
• The Efficacy and Influencing Factors of Polymyxin B in High-Level Carbapenem-Resistant Klebsiella pneumoniae Infections (Infection and Drug Resistance, 2023)
• Clinical translation of polymyxin-based combination therapy: Facts, challenges and future opportunities (The Journal of Infection, 2017)
• TIGRIS and EUPHRATES eventually join and provide new evidence: a narrative review of the polymyxin B hemoperfusion (Journal of Intensive Care, 2025)
• The wind changed direction and the big river still flows: from EUPHRATES to TIGRIS (Journal of Intensive Care, 2019)
• Polymyxin B adjuvants against polymyxin B- and carbapenem-resistant Gram-negative bacteria (Future Microbiology, 2024)
• Hyperforin potentiates polymyxin B against multidrug-resistant Gram-negative pathogens via membrane disruption, biofilm eradication, and oxidative stress (Antimicrobial Agents and Chemotherapy, 2025)
• Antibacterial activity of gallium nitrate against polymyxin-resistant Klebsiella pneumoniae strains (Diagnostic Microbiology and Infectious Disease, 2022)
• Discovery of Novel Polymyxin-Like Antibiotics (Advances in Experimental Medicine and Biology, 2019)