Peptide library / Immune & defense / Polymyxin B
Polymyxin B
A last-resort cyclic peptide antibiotic, close relative of colistin.
Effects studied or claimed
What it is used or promoted for, and where each effect has actually been seen
- Multidrug-resistant Gram-negative infectionsFDA approved
How it is thought to work
Polymyxin B binds the outer membrane of Gram-negative bacteria and breaks it open.
What the evidence shows
Used for decades and revived because of resistant bacteria. Evidence is mostly observational.
Safety and unknowns
Kidney and nerve toxicity are common and dose limiting. It carries boxed warnings.
Regulatory status
FDA-approved.
Regulatory status changes quickly. This entry was last reviewed on 27 October 2026. Confirm current status with the FDA before relying on it.
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General information, not medical advice. Do not buy or inject unregulated peptides.