Evidence Grade A — Regulatory approved. 7111 published studies. 68 registered clinical trials.
Medically reviewed by a licensed medical professional
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Polymyxin B is a close relative of colistin, used as a last-resort intravenous antibiotic for gram-negative infections resistant to virtually all other drugs. Outside of critical care, most people encounter polymyxin B as an ingredient in over-the-counter antibiotic creams like Neosporin and eye drops like Polytrim — where the tiny amounts applied topically pose no systemic toxicity concerns.
Polymyxin B is also known by these brand and alternate names:
7,111 published studies: 3112 human, 1736 animal, 1297 in-vitro, 308 reviews
Polymyxin B is marketed as Poly-Rx (injection, approved approximately 1964) and is a component of numerous topical products including Neosporin, Cortisporin, and Polytrim. Intravenous polymyxin B and colistin are generally considered interchangeable for systemic infections.
Recent international consensus guidelines recommend targeting specific blood level thresholds for intravenous polymyxin B. Kidney injury rates are comparable to colistin (approximately 40–45%), but polymyxin B may cause more neurotoxicity (all reversible). Outside of critical care, the vast majority of polymyxin B use is in over-the-counter topical antibiotic combinations for minor skin wounds and eye infections, where systemic toxicity is not a concern.
Polymyxin B works through the same fundamental mechanism as colistin — binding to lipid A on the gram-negative bacterial outer membrane, disrupting membrane integrity, and causing cell death. The key pharmacological difference is that polymyxin B is given in its active form, while colistin is given as an inactive prodrug that must be converted in the body. This means polymyxin B reaches effective concentrations more rapidly and predictably, which matters in critically ill patients.
Like colistin, polymyxin B was approved decades before modern trial standards, so its evidence base consists largely of observational data from critically ill patients. Kidney injury occurs in approximately 40-45% of patients receiving intravenous polymyxin B — comparable to colistin — though it may cause more neurological side effects. The pharmacological advantage over colistin is that polymyxin B is administered in its active form, reaching effective blood levels more rapidly and predictably. Colistin is given as an inactive prodrug that must be converted in the body, introducing variability. For critically ill patients, this predictability matters. International guidelines now recommend specific blood level targets for intravenous polymyxin B. No large randomised trials have compared it against newer antibiotics.
PeptideTrace tracks 68 registered clinical trials for Polymyxin B sourced from ClinicalTrials.gov.
Treatment of Acyclovir-Resistant Mucocutaneous Herpes Simplex Disease in Patients With AIDS: Open Label Pilot Study of Topical Trifluridine
Open-label Evaluation of Polymyxin B Hemoperfusion for Septic Shock
Evaluating the Use of Polymyxin B Cartridge Hemoperfusion for Patients With Septic Shock and COVID 19
Safety, Pharmacokinetics and Efficacy of BV100 Plus Low Dose Polymyxin B Plus Ceftazidime/Avibactam, or Plus Cefiderocol in Patients With Pulmonary and Extrapulmonary Infections Due to Carbapenem-resistant Acinetobacter Baumannii-calcoaceticus Complex
A Phase I Study Comparing the Safety, Pharmacokinetics and Renal Effects of VRP-034 and Marketed Polymyxin B in Healthy Volunteers
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Polymyxin B is a cyclic lipopeptide decapeptide (10 AA), MW ~1,203 Da (polymyxin B1, ~75%). Cyclic heptapeptide ring plus tripeptide, five Dab residues, N-terminal 6-methyloctanoic acid. D-Phenylalanine at position 6 (vs. D-Leu in colistin). Administered directly as active drug (not prodrug). Half-life ~9-11.5 hours. Primarily non-renal elimination. IV 15,000-25,000 units/kg/day q12h.
Parallels colistin: cationic Dab residues bind lipid A, displacing divalent cations; hydrophobic chain and D-Phe-L-Leu segment insert into membrane causing pore formation and osmotic lysis. Additional: endotoxin neutralization (exploited by Toraymyxin hemoperfusion), respiratory chain inhibition, phospholipid exchange. D-Phe-L-Leu forms type II' beta-turn for membrane insertion.
Marketed as Poly-Rx (injection; approved ~1964). Combination products: Neosporin, Cortisporin, Polytrim. Rigatto et al. (2015; N=290): comparable AKI rates to CMS (44.7% vs. 40.0%), higher neurotoxicity (16.9% vs. 1.4%, all reversible). 2019 International Consensus: AUCss target 50-100. Indications: UTIs, meningitis, bloodstream infections; ophthalmic; topical combinations.
Vancomycin is marketed as Vancocin and Firvanq (approved 1958, with oral solution Firvanq approved 2018). It is the standard treatment for serious MRSA infections (bloodstream infections, endocarditis, pneumonia, bone infections) and is first-line for severe C. difficile colitis. Vancomycin requires therapeutic drug monitoring — blood levels must be checked regularly to ensure the dose is effective without causing kidney damage or hearing loss. The rise of vancomycin-resistant enterococci (VRE) and occasional vancomycin-intermediate S. aureus (VISA) strains represent ongoing challenges. Despite being nearly 70 years old, vancomycin remains irreplaceable for many serious infections, though newer alternatives like daptomycin and the lipoglycopeptides offer advantages in specific settings.
Zilucoplan is marketed as Zilbrysq (approved October 2023) for anti-acetylcholine receptor antibody-positive generalised myasthenia gravis in adults. Administered as a daily subcutaneous self-injection. In the RAISE trial, zilucoplan showed statistically significant improvements in both activities of daily living and quantitative muscle strength scores compared to placebo, with improvements evident from week one. Its key differentiator from existing complement inhibitors (eculizumab, ravulizumab) is the self-injectable format — those alternatives require hospital-based intravenous infusions. As with all complement inhibitors, patients require meningococcal vaccination before starting treatment due to increased susceptibility to meningococcal infection.
Daptomycin is marketed as Cubicin (approved September 2003). It is indicated for complicated skin and soft tissue infections and S. aureus bloodstream infections including right-sided endocarditis. Administered as a once-daily intravenous infusion. A key limitation is that daptomycin cannot be used for pneumonia — lung surfactant inactivates the drug. In the bacteraemia trial, daptomycin was non-inferior to vancomycin with significantly lower rates of kidney problems (11% versus 26%). Creatine kinase (CK) levels must be monitored during treatment, as daptomycin can cause muscle toxicity. Generics became available after patent expiry, significantly reducing cost.
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