Murepavadin

What is Murepavadin?

Murepavadin is an investigational antibiotic with an unusual pedigree and an unusual failure. It is a macrocyclic peptidomimetic — a backbone-cyclised peptide built on a D-proline-L-proline template that locks it into a beta-hairpin shape — derived from protegrin-I, a host-defence peptide found in pig leukocytes. The molecule is C73H112N22O16 with a molecular weight of about 1554 (PubChem CID 91824766), and it has been known as POL7080 in the Polyphor literature and RG7929 during its time at Roche. Its defining feature is a mechanism no other clinical antibiotic uses. Murepavadin binds LptD, the outer-membrane protein that inserts lipopolysaccharide into the final layer of the Gram-negative envelope. Blocking LptD stops the bacterium from building its own outer membrane. Crucially, this is a non-lytic mechanism: unlike almost every other membrane-active peptide, murepavadin does not punch holes in the bacterium, it jams a specific piece of machinery. That is why it was described as the first in class of outer membrane protein targeting antibiotics, usually abbreviated OMPTA. The second unusual feature is that it is pathogen-specific. Murepavadin is active against Pseudomonas aeruginosa and essentially nothing else, because the LptD it binds is Pseudomonas-specific. In an era of broad-spectrum antibiotics and collateral damage to the microbiome, a drug that hits one species is a genuine design achievement — and a commercial liability, since it can only be used once the organism is identified or strongly suspected. Its activity against resistant Pseudomonas was what made it exciting. Murepavadin retains potent in vitro activity against carbapenemase-producing and colistin-resistant isolates, which are among the hardest organisms in hospital medicine. That is why its failure mattered to a field with very few options.

What Murepavadin Is Investigated For

Murepavadin is best understood as a failed drug whose failure taught the field something. There is no live clinical programme, and the page exists because the compound is still cited constantly in antimicrobial peptide and Gram-negative antibiotic research, and because the reasons it failed bear directly on every peptide antibiotic that follows it. The intravenous programme reached Phase 3. Two pivotal trials ran in parallel from 2018 — PRISM-UDR in nosocomial pneumonia due to Pseudomonas aeruginosa and PRISM-MDR in ventilator-associated pneumonia — and both were terminated on 17 July 2019, with the registry entries citing safety data review. The trigger was acute kidney injury. Reporting at the time described 18 of 32 evaluable patients in the murepavadin arm of PRISM-MDR (56 percent) with acute kidney injury against an expected background rate of 25 to 40 percent in this population, with 41 percent of those meeting KDIGO stage 2 or 3 criteria. Polyphor first paused enrolment in May 2019 and then abandoned both trials, keeping the inhaled programme alive on the grounds that it would produce far lower systemic exposure. The inhaled programme has since stopped too. Spexis — the company formed from Polyphor — reported first-in-human results in January 2023 showing inhaled murepavadin was well tolerated at all dose levels with no serious adverse events and systemic bioavailability below 5 percent, which was exactly the result the strategy predicted. The Cystic Fibrosis Foundation's drug development pipeline now lists inhaled murepavadin as discontinued, stating that preclinical laboratory studies were completed and no further development in cystic fibrosis is planned. Some drug databases still show it as an active Phase 1 asset; the Foundation's own listing is the better source. What survives is the science. Murepavadin established that LptD is a druggable antibiotic target, that pathogen-specific antibiotics are chemically achievable, and — through the resistance work that followed — that escaping murepavadin costs the bacterium something, because the lipopolysaccharide changes that confer resistance also make the organism more vulnerable to the host's own antimicrobial peptides.

History & Discovery

Murepavadin began with protegrin-I, a cationic beta-hairpin peptide isolated from pig leukocytes in the early 1990s and shown to be broadly and potently antimicrobial by membrane disruption. Protegrin itself was a poor drug candidate — it was haemolytic, unstable and indiscriminate — but its hairpin architecture was a useful scaffold. Work at the University of Zurich under John Robinson established that the hairpin could be stabilised by building it onto a D-proline-L-proline template, producing conformationally locked macrocycles whose properties could then be tuned by varying the sequence around the loop. The decisive discovery, around 2010, was that iterative optimisation of these protegrin-derived macrocycles produced compounds that had stopped killing by membrane lysis altogether and had instead acquired a specific protein target: LptD in Pseudomonas aeruginosa. This was a conceptual shift. The field had assumed peptide antibiotics were essentially membrane-active agents; here was a peptide-derived molecule that behaved like a conventional target-based antibiotic, with all the specificity that implies. Polyphor, the Swiss company spun out of the Zurich work, developed the lead as POL7080 and the class as outer membrane protein targeting antibiotics. The commercial history was turbulent. The FDA granted Qualified Infectious Disease Product designation. In November 2013, Roche licensed the compound — paying CHF 35 million upfront with up to CHF 465 million in milestones plus tiered double-digit royalties — and developed it as RG7929. Roche subsequently handed the compound back, stating that a streamlined development path as originally planned was no longer an option for it, and Polyphor continued alone, taking the drug into Phase 3 in 2018. The end came quickly. In May 2019, Polyphor paused enrolment in both pivotal trials after acute kidney injury in the murepavadin arm of PRISM-MDR exceeded expectations. On 17 July 2019 both trials were terminated, and the intravenous programme was abandoned. Polyphor kept the inhaled formulation, merged with EnBiotix in 2022 to become Spexis AG, and reported encouraging first-in-human inhaled data in January 2023 — but by the time of writing the Cystic Fibrosis Foundation lists inhaled murepavadin as discontinued, with no further development planned. The target it validated outlived the molecule: LptD remains an actively pursued antibiotic target, and murepavadin is the proof that it can be hit.

How It Works

Gram-negative bacteria are wrapped in a tough outer membrane that keeps most antibiotics out. Building that membrane requires ferrying a greasy molecule called lipopolysaccharide to the surface and slotting it into place, and the protein that does the slotting is called LptD. Murepavadin grabs hold of LptD in Pseudomonas aeruginosa and stops it working. The bacterium can no longer finish its own armour and dies. Unlike most peptide antibiotics, murepavadin does not rip the membrane open — it disables a specific machine, which is why it kills Pseudomonas and leaves other bacteria alone.

Murepavadin is a backbone-cyclised beta-hairpin peptidomimetic. Its scaffold comes from protegrin-I, a cationic host-defence peptide of pig leukocytes, which was progressively redesigned by John Robinson's group at the University of Zurich and by Polyphor around a D-proline-L-proline template that enforces the hairpin conformation. Successive rounds of optimisation moved the molecule away from protegrin's original lytic, broad-spectrum character and toward a specific protein target — a transition that is worth appreciating, because it means murepavadin is not a membrane-disrupting peptide that happens to be selective, it is a protein-binding drug that happens to be built from amino acids. Its synthesis has since been achieved by tandem native chemical ligation and desulfurisation, an epimerisation-free route to the cyclised backbone. The target is LptD, the final component of the lipopolysaccharide transport (Lpt) pathway. Lipopolysaccharide is synthesised at the inner membrane and must be shuttled across the periplasm and inserted into the outer leaflet of the outer membrane; LptD, working with the lipoprotein LptE, forms the translocon that performs that insertion. Blocking it prevents assembly of the outer membrane. The consequences are described in the literature as outer membrane alterations rather than lysis, and the mechanism is explicitly non-lytic — which distinguishes murepavadin from essentially every other antimicrobial peptide in or near clinical use. Specificity derives from the target. Murepavadin binds the Pseudomonas aeruginosa form of LptD and is inactive against other Gram-negatives. Against its target organism it is potent: in cystic fibrosis isolates the MIC50 was 0.125 mg/L and the MIC90 2 mg/L by broth microdilution, and it was bactericidal at 32 mg/L against 95.4 percent of strains within one to five hours. Activity was preserved in the presence of artificial sputum and lung surfactant, which is why the inhaled route looked promising. One methodological detail matters for anyone reading the microbiology: broth microdilution and agar dilution give very different numbers for this compound — MIC50 0.125 versus 4 mg/L, MIC90 2 versus 32 mg/L — so results are not comparable across methods. Resistance arises through lipopolysaccharide remodelling rather than through target mutation alone. Whole-genome sequencing of resistant mutants identified changes in lpxL1, lpxL2, bamA, lptD, lpxT, msbA and pmrB. A 2024 genome-wide association study across 496 clinical isolates found no single genetic event explaining the phenotype, but confirmed that lpxL1 and lpxL2 mutations with loss of hexa-acylated lipid A drive high-level resistance. The same alterations reduced the inflammatory response of human monocytes to the mutant lipopolysaccharide and increased the bacterium's susceptibility to host-derived cathelicidin and indolicidin — a fitness cost paid in exchange for escaping the drug.

Evidence Snapshot

Research Gaps & Open Questions

What the current literature has not yet settled about Murepavadin:

• 01What causes murepavadin's nephrotoxicity? No published mechanistic work explains it. Whether it reflects proximal tubular uptake and accumulation of a cationic peptide — the mechanism established for the polymyxins — or something specific to this scaffold has never been determined, and the answer would inform the design of every peptide antibiotic that follows.
• 02Was there a safe exposure window? The programme was stopped rather than de-escalated, so whether a lower-dose or renally adjusted regimen with therapeutic drug monitoring could have retained efficacy is unknown. Because the Phase 3 trials never read out, it is not even known whether the drug worked.
• 03Did the kidney injury resolve? No published source describes renal recovery in the affected patients. For a drug class with a future, the difference between reversible and permanent injury would matter enormously.
• 04Is the inhaled route viable over months? A single first-in-human study showed tolerability and systemic bioavailability below 5 percent. Chronic inhaled antibiotic therapy in cystic fibrosis runs for years in alternating cycles, and nothing is known about long-term airway tolerability, resistance emergence under chronic exposure, or efficacy.
• 05How quickly does resistance emerge in patients rather than in vitro? Spontaneous resistant mutants arise readily in the laboratory with MIC increases of two to nine two-fold dilutions, but the clinical rate was never measured because no completed efficacy trial exists.
• 06Can the fitness cost of resistance be exploited? The finding that lpxL-mutant resistant strains lose hexa-acylated lipid A and become more susceptible to host cathelicidin and indolicidin suggests resistance comes with a defensive penalty. Whether that could be turned into a therapeutic strategy — pairing an LptD inhibitor with something that exploits the resulting vulnerability — is an open and genuinely interesting question.
• 07Are there LptD inhibitors without the renal liability? This is the question the field actually cares about. Murepavadin validated the target; whether the toxicity was intrinsic to hitting LptD, intrinsic to cationic macrocyclic peptides, or specific to this molecule determines whether the class has a future.

Forms & Administration

Murepavadin was developed as an intravenous infusion for hospital-acquired and ventilator-associated pneumonia. Phase 1 studies used single doses around 2.2 milligrams per kilogram infused over three hours, and the Phase 3 programme used multiple daily intravenous doses alongside standard-of-care Gram-negative cover. That formulation was discontinued in 2019. A dry-powder or nebulised inhaled formulation was subsequently developed for chronic Pseudomonas infection in cystic fibrosis, on the rationale that delivering the drug directly to the airway would achieve high local concentrations while limiting systemic exposure and therefore kidney exposure. The first-in-human study reported systemic bioavailability below 5 percent, which validated the rationale — but the programme has since been discontinued. There is no approved product, no commercial supply, and no legitimate access route of any kind. Murepavadin exists today as a research compound used in microbiology laboratories to study LptD biology and Pseudomonas resistance, and material offered for sale outside that context should not be assumed to be what it claims.

Dosing & Protocols

The ranges below reflect protocols commonly discussed in the literature and by clinicians — not a prescription. Actual dosing for any individual should be determined by a qualified healthcare provider who knows the patient.

Murepavadin is an unapproved investigational antibiotic whose intravenous development was halted for nephrotoxicity and whose inhaled development has been discontinued. It is not available through any legitimate channel, has no established safe dose in humans, and has no application outside a microbiology laboratory.

Timeline of Effects

Common Questions

Who Murepavadin Is NOT For

Drug & Supplement Interactions

Formal interaction data are limited to a single published study. A Phase 1 drug-drug interaction trial examined murepavadin with amikacin, reflecting the expectation that the two would be used together against resistant Pseudomonas in ventilated patients. That combination is the interaction of greatest practical concern for an entirely different reason than pharmacokinetics: aminoglycosides are themselves nephrotoxic, and the trial population for the Phase 3 programme was precisely the group most likely to be receiving them. Because murepavadin is a cyclic peptide cleared substantially by renal routes rather than hepatic metabolism, cytochrome P450 interactions are not the issue. The issue is additive renal injury. Any agent that reduces renal clearance will increase murepavadin exposure, which in turn increases renal risk — the renal impairment pharmacokinetic study showed a 2.0 to 2.5-fold exposure increase in impaired subjects — and any agent that is itself nephrotoxic adds directly to the hazard. Vancomycin, colistin, amphotericin B, contrast media, NSAIDs and ACE inhibitors would all have warranted attention had the drug reached clinical use. The inhaled formulation changes this picture substantially, since systemic bioavailability below 5 percent means the kidney sees very little drug. Interaction concerns for an inhaled antibiotic are mainly local — compatibility with other nebulised therapies and the sequencing of airway clearance — and none of these were characterised before the programme was discontinued.

Safety Profile

Legal Status

Regulatory status changes over time. Verify current local rules with a qualified professional.

Myths & Misconceptions