Antimicrobial peptides (AMPs) are short chains of amino acids that kill microbes, and researchers have studied them for decades as a fix for antibiotic resistance. The quick answer: a handful of peptide antibiotics made by microbes, such as colistin, polymyxin B and daptomycin, are already approved,[2][3][4] but no human-style host-defense peptide has yet been approved as an antibiotic. Late-stage failures, safety problems and cost have stalled most candidates.[1]
This page is part of our peptide basics hub. For how the body’s own AMPs differ, see LL-37 vs defensins vs magainin.
Bottom line
- Established: cyclic peptide antibiotics from bacteria and fungi are in routine hospital use, mostly as last-resort or specialist drugs.[2][3]
- Established: bacteria can evolve resistance to AMPs, in the lab and in the clinic.[6][7]
- Preliminary: anti-biofilm peptides look promising in lab dishes, with no approved product.[5]
- Unproven: no host-defense peptide has passed a phase 3 trial as a systemic antibiotic.[1][10]
How antimicrobial peptides work
Most AMPs are 10 to 50 amino acids long and carry a positive charge. Bacterial membranes are negatively charged, so the peptides stick to them and many punch holes or disrupt the membrane. Some also slip inside to block bacterial processes, and several calm or steer the immune system.[1]
Because they attack the membrane rather than one enzyme, AMPs were long thought to be hard for bacteria to resist. They also work against some biofilms, the slimy communities of bacteria on wounds, catheters and implants that tolerate standard antibiotics.[1][5]
Which peptide antibiotics are approved?
It helps to separate two groups. “Host-defense peptides” are made by animals and people as part of innate immunity. “Peptide antibiotics” are mostly made by bacteria or fungi and are often ring-shaped (cyclic) with a fatty tail. Only the second group is approved for treating infections.
| Drug | Type | Status | Main use |
|---|---|---|---|
| Polymyxin B, colistin (polymyxin E) | Cyclic lipopeptides from bacteria | Approved for decades | Last-resort treatment of multidrug-resistant Gram-negative infections[2] |
| Daptomycin | Cyclic lipopeptide from bacteria | FDA-approved 2003 | Gram-positive infections such as MRSA bloodstream infections[3][4] |
| Pexiganan (magainin analogue) | Synthetic host-defense-style peptide | Not approved; failed phase 3 in 2016 | Infected diabetic foot ulcers[9] |
| Murepavadin | Synthetic cyclic peptide | IV phase 3 stopped in 2019 | Pseudomonas pneumonia[10] |
| LL-37 | Human host-defense peptide | Not approved anywhere | Studied as a wound treatment (profile) |
Vancomycin and its relatives are sometimes called peptide antibiotics too, but they are glycopeptides, a separate class built on a short peptide core with sugars attached. For other approved peptide medicines across all fields, see our FDA-approved peptides list. Many of these drugs are ring-shaped; our guide to cyclic peptides explains why that matters.
The polymyxins show both the promise and the problem. They work against some of the hardest bacteria, but kidney toxicity limits dosing, and international guidelines spend much of their advice on dosing them safely.[2]
Key studies
Pexiganan, the closest call. Pexiganan is a 22-amino-acid synthetic version of magainin, a frog-skin peptide. In two earlier double-blind trials with 835 patients, pexiganan cream matched oral ofloxacin for mildly infected diabetic foot ulcers, with clinical improvement in 85% to 90% of patients in both groups and no significant resistance to pexiganan.[8] But in 2016, two newer phase 3 trials (OneStep-1 and -2, 389 patients) found it did no better than a placebo cream added to standard wound care, on infection or wound closure.[9]
Murepavadin. This cyclic peptide targets a transport protein found in Pseudomonas aeruginosa. Its IV phase 3 trial in ventilator-associated pneumonia enrolled 41 patients before it was terminated in July 2019 after a safety data review.[10] Development has since focused on an inhaled form.[11]
Biofilms. In a 2014 lab study, a synthetic peptide called 1018 blocked a bacterial stress signal and both prevented and broke up biofilms of Pseudomonas, E. coli, Klebsiella, Acinetobacter and MRSA, at doses that did not kill free-floating bacteria. The authors noted that no approved drug specifically targets biofilms.[5] These results come from lab models, not patients.
Can bacteria become resistant?
Yes. The idea that AMPs are “resistance-proof” has not held up.
- In the lab: when E. coli and Pseudomonas fluorescens were grown with rising amounts of pexiganan for 600 to 700 generations, 22 of 24 lines evolved inherited resistance.[6]
- In the clinic: in 2015, Chinese researchers found a gene, mcr-1, that gives bacteria colistin resistance and can jump between bacteria on a plasmid. It was present in E. coli from 15% of raw meat samples, 21% of farm animals and 1% of hospital patients tested.[7]
- With daptomycin: resistance in staph and enterococci is uncommon but rising, mostly during long courses or heavy infections.[3]
A further worry is that resistance to a therapeutic AMP might also blunt the body’s own defense peptides, since they work in similar ways.[1]
Why so few make it to approval
Reviews point to the same hurdles again and again:[1]
- Short life in the body: enzymes in blood and tissue break peptides down fast.
- Toxicity: membrane-disrupting peptides can also harm human cells, and the polymyxins can damage kidneys.[2]
- Cost: making long peptides at scale is expensive compared with small-molecule antibiotics.
- Topical vs systemic: most candidates work best on skin or wounds, where proving an advantage over existing care has been hard.
Our natural vs synthetic peptides guide explains how chemists modify peptides to last longer.
Limitations of the research
- Most AMP data come from test tubes and animals, where doses and conditions differ from patients.
- Trials have often compared a peptide with an active drug, which can show “no worse” but not “better.”
- Several programs ended for business reasons, so negative findings are not always fully published.
What’s next
Engineered peptides are now being tested in narrower uses. The RETAIN trial, a phase 2/3 placebo-controlled study, is giving PLG0206 as a rinse during surgery for infected knee replacements; it aims to enroll 240 people, with primary completion listed for September 2028.[12] Polymyxin derivatives designed to be gentler on kidneys are also in early trials.[11] For AMPs in skin and wound treatment, see our guide to antimicrobial peptides in wound care, and for the human defensin family, defensins in clinical development.
Questions to discuss with a clinician
- Is my infection one where a peptide antibiotic such as daptomycin or colistin is appropriate?
- What kidney or nerve monitoring is needed with these drugs?
- Are there clinical trials for my type of resistant infection?
- Why shouldn’t I use unapproved “research” antimicrobial peptides for an infection?
