Introduction
Aztreonam avibactam for NDM-producing Enterobacterales has become an important area of interest in the management of antimicrobial-resistant Gram-negative infections.
NDM, or New Delhi metallo-β-lactamase, is a metallo-β-lactamase (MBL) that can hydrolyze many β-lactam antibiotics, including carbapenems. However, aztreonam has a distinctive property: it is stable to hydrolysis by MBLs such as NDM.
The challenge is that NDM-producing bacteria frequently carry additional β-lactamases, including ESBLs, AmpC enzymes, and some OXA-type enzymes. These enzymes can hydrolyze aztreonam.
This is where avibactam becomes important.
The aztreonam-avibactam combination is designed so that aztreonam can retain its antibacterial activity while avibactam inhibits susceptible serine β-lactamases that would otherwise degrade aztreonam.
The 2026 IDSA guidance identifies aztreonam-avibactam and cefiderocol as preferred treatment options for invasive infections caused by NDM-producing Enterobacterales, while also emphasizing the limitations of available clinical outcome data.
What Are NDM-Producing Enterobacterales?
Enterobacterales are a large group of Gram-negative bacteria that includes clinically important organisms such as:
- Escherichia coli
- Klebsiella pneumoniae
- Enterobacter species
- Citrobacter species
- Proteus species
Some of these organisms can acquire carbapenemase genes, including blaNDM.
NDM enzymes belong to the metallo-β-lactamase family and can hydrolyze many β-lactam antibiotics.
This can leave clinicians with limited treatment options, particularly when NDM production occurs alongside other resistance mechanisms.
Why Is NDM Difficult to Treat?
NDM creates a particular therapeutic challenge because it can hydrolyze most conventional β-lactam antibiotics.
Importantly, however, NDM does not efficiently hydrolyze aztreonam.
That creates the basic rationale for combining aztreonam with avibactam.
The problem is that NDM-producing organisms often produce additional β-lactamases.
For example, an NDM-producing E. coli may also produce:
- ESBLs
- CMY-type AmpC enzymes
- OXA-type β-lactamases
- Other resistance mechanisms affecting permeability or antibiotic target susceptibility
Therefore, aztreonam may remain vulnerable to enzymes that are not NDM itself.
How Does Aztreonam Avibactam Work Against NDM?
The combination uses two complementary mechanisms.
1. Aztreonam avoids NDM hydrolysis
Aztreonam is a monobactam antibiotic that targets bacterial cell-wall synthesis, primarily through binding to PBP3.
Unlike many other β-lactams, aztreonam is stable against hydrolysis by NDM and other metallo-β-lactamases.
This allows it to retain activity in the presence of NDM.
2. Avibactam inhibits susceptible serine β-lactamases
Avibactam does not directly inhibit NDM.
Instead, it inhibits several serine β-lactamases, including many class A and class C enzymes.
This can prevent enzymes such as ESBLs and AmpC from destroying aztreonam.
3. The combination protects aztreonam
The overall concept can therefore be summarized as:
NDM does not effectively destroy aztreonam → avibactam inhibits accompanying serine β-lactamases → aztreonam can reach PBP3 and inhibit cell-wall synthesis.
This complementary mechanism is the foundation of aztreonam-avibactam activity against NDM-producing Enterobacterales.
Aztreonam Avibactam and NDM: Why the Combination Matters
The distinction between NDM and other β-lactamases is important.
Avibactam is not an NDM inhibitor.
Instead, the combination works because the two components address different resistance mechanisms:
| Resistance mechanism | Role in aztreonam-avibactam |
|---|---|
| NDM metallo-β-lactamase | Aztreonam is stable to NDM hydrolysis |
| ESBL | Avibactam inhibits susceptible ESBLs |
| AmpC | Avibactam inhibits susceptible AmpC enzymes |
| PBP3 alterations | Can reduce aztreonam activity |
| Porin loss | Can reduce antibiotic entry |
| Efflux | Can contribute to reduced susceptibility |
This explains why resistance testing remains important even when an NDM gene has been identified.
Aztreonam Avibactam Susceptibility in NDM-Producing Enterobacterales
Susceptibility testing provides important information when evaluating an NDM-producing isolate.
The 2026 IDSA guidance reports that, using the CLSI susceptible breakpoint of ≤4/4 µg/mL, more than 95% of NDM-producing Enterobacterales in cited surveillance datasets were susceptible to aztreonam-avibactam.
However, surveillance susceptibility should not be interpreted as a guarantee of clinical response.
Individual isolates can contain additional resistance mechanisms, and susceptibility patterns can vary by species, enzyme combination and geographic setting.
Why AST Still Matters
Identification of an NDM carbapenemase does not eliminate the need for antimicrobial susceptibility testing.
Laboratory testing can help determine whether the individual isolate remains susceptible to aztreonam-avibactam.
This is particularly important because resistance mechanisms involving PBP3, AmpC enzymes, porin changes and other pathways can reduce activity.
Aztreonam Avibactam Resistance in NDM-Producing E. coli
One of the most important emerging resistance mechanisms involves alterations in PBP3.
Specific four-amino-acid insertions, including variants such as YRIN and YRIK, have been associated with reduced susceptibility to aztreonam-avibactam.
These alterations can become particularly important when they occur together with certain CMY-type AmpC enzymes.
This combination of target modification and β-lactamase production can significantly reduce the effectiveness of the aztreonam-avibactam combination.
The 2026 IDSA guidance notes that these PBP3-associated resistance mechanisms have been described in NDM-producing E. coli and are increasingly being recognized outside regions where they were initially reported.
NDM-Producing Klebsiella pneumoniae
Resistance mechanisms can differ between bacterial species.
In NDM-producing Klebsiella pneumoniae, reported mechanisms associated with aztreonam-avibactam resistance include:
- Porin alterations
- Increased efflux
- Changes in plasmid-mediated AmpC enzymes
- CMY-type β-lactamase variants
This highlights an important principle in antimicrobial resistance:
The presence of the same carbapenemase does not necessarily mean that all bacterial isolates will have the same susceptibility profile.
Species, genetic background and additional resistance determinants can all influence susceptibility.
Clinical Evidence for Aztreonam Avibactam in NDM Infections
Clinical evidence for aztreonam-avibactam against NDM-producing Enterobacterales is growing, but it remains more limited than the extensive in-vitro susceptibility literature.
The 2026 IDSA guidance describes clinical outcome data primarily from subgroup analyses of clinical trials.
In one subgroup containing six patients with NDM-producing Enterobacterales infections, clinical cure occurred in 2 of 6 patients (33%) receiving aztreonam-avibactam, while 28-day survival was 5 of 6 patients (83%).
Because these numbers are based on very small subgroups, they should not be interpreted as definitive estimates of treatment effectiveness.
Another clinical trial subgroup reported clinical cure in 4 of 9 patients (44%) receiving aztreonam-avibactam, with 28-day survival of 8 of 9 patients (89%).
Again, the small sample size limits how broadly these findings can be applied.
Aztreonam Avibactam vs Other Options for NDM
The treatment landscape for NDM-producing Enterobacterales includes several newer antimicrobial strategies.
The 2026 IDSA guidance identifies aztreonam-avibactam and cefiderocol as preferred options for invasive NDM-producing Enterobacterales infections.
Ceftazidime-avibactam combined with aztreonam is another strategy when aztreonam-avibactam is unavailable.
Importantly, direct comparative clinical data between aztreonam-avibactam and cefiderocol remain limited.
Therefore, laboratory susceptibility results, infection characteristics and patient-specific clinical factors remain important when selecting therapy.
Aztreonam Avibactam and MBL-Producing Bacteria
NDM is one member of the broader metallo-β-lactamase family.
Other MBLs include:
- VIM
- IMP
- NDM
The same general mechanistic principle applies: aztreonam can remain stable against MBL-mediated hydrolysis, while avibactam protects aztreonam against susceptible serine β-lactamases.
However, activity can vary significantly depending on the organism and its additional resistance mechanisms.
For example, the 2026 IDSA guidance does not suggest aztreonam-avibactam for MBL-producing Pseudomonas aeruginosa, where activity is limited and standardized CLSI/FDA susceptibility breakpoints are not available.
Therefore, evidence for NDM-producing Enterobacterales should not automatically be extrapolated to MBL-producing P. aeruginosa.
Role of Susceptibility Testing
Susceptibility testing remains an essential part of evaluating aztreonam-avibactam activity.
For Enterobacterales, the 2026 IDSA guidance lists a CLSI susceptible breakpoint of ≤4/4 µg/mL for aztreonam-avibactam.
Testing can help identify isolates that remain susceptible despite the presence of NDM.
It can also help detect situations where additional resistance mechanisms may compromise the combination.
For more information, see our detailed guide:
[Aztreonam Avibactam Susceptibility Testing: MIC, Breakpoints and Methods]
https://aioniospharma.com/aztreonam-avibactam-susceptibility-testing/
Aztreonam Avibactam: Mechanism and PK/PD Considerations
The activity of aztreonam-avibactam depends on maintaining adequate exposure to both components.
Development of the combination has incorporated joint pharmacodynamic targets, including:
- Aztreonam: ≥60% fT>MIC
- Avibactam: ≥50% fT>2.5 µg/mL
These targets help explain why the fixed combination was developed to provide synchronized exposure to aztreonam and avibactam.
For a deeper explanation, see:
[Aztreonam Avibactam Pharmacokinetics: Half-Life, Clearance & PK/PD]
https://aioniospharma.com/aztreonam-avibactam-pharmacokinetics/
Where Meblanios Fits Into the Aztreonam Avibactam Landscape
Meblanios is an aztreonam-avibactam injection from AIONIOS Pharma.
When discussing a specific product, it is important to distinguish product information from the broader scientific and clinical evidence surrounding aztreonam-avibactam as an active combination.
For product-specific information, refer to the official product page:
[Meblanios – Aztreonam Avibactam Injection]
https://aioniospharma.com/product/meblanios/
This distinction helps keep educational information about aztreonam-avibactam separate from product-specific claims.
Key Takeaways
- NDM is a metallo-β-lactamase that can hydrolyze many β-lactam antibiotics.
- Aztreonam is relatively stable against NDM-mediated hydrolysis.
- Avibactam does not inhibit NDM directly.
- Avibactam inhibits susceptible serine β-lactamases that can otherwise hydrolyze aztreonam.
- The combination therefore addresses complementary resistance mechanisms.
- More than 95% of NDM-producing Enterobacterales in cited surveillance datasets were susceptible using the CLSI breakpoint referenced by the 2026 IDSA guidance.
- PBP3 alterations and CMY-type AmpC enzymes are important emerging resistance mechanisms.
- Clinical evidence in NDM infections remains limited and is largely based on small subgroup analyses.
- Susceptibility testing remains important for individual isolates.
- Evidence for NDM-producing Enterobacterales should not automatically be applied to MBL-producing Pseudomonas aeruginosa.
Frequently Asked Questions
What is aztreonam avibactam used for in NDM infections?
Aztreonam-avibactam is an important treatment option for infections caused by NDM-producing Enterobacterales. The 2026 IDSA guidance lists it among the preferred options for invasive NDM-producing Enterobacterales infections.
Does avibactam inhibit NDM?
No. Avibactam does not directly inhibit NDM because NDM is a metallo-β-lactamase. Avibactam instead inhibits susceptible serine β-lactamases that may be produced alongside NDM.
Why can aztreonam work against NDM?
Aztreonam is structurally different from many other β-lactam antibiotics and is stable against hydrolysis by NDM and other metallo-β-lactamases.
Can NDM-producing bacteria become resistant to aztreonam-avibactam?
Yes. Resistance can develop or occur through mechanisms such as PBP3 alterations, AmpC variants, porin changes and efflux-related mechanisms.
Is aztreonam-avibactam effective against every MBL-producing bacterium?
No. Activity depends on the organism and its resistance mechanisms. Evidence supporting aztreonam-avibactam in NDM-producing Enterobacterales should not automatically be extrapolated to MBL-producing Pseudomonas aeruginosa.
Why is susceptibility testing important?
Susceptibility testing helps determine whether an individual bacterial isolate is susceptible to aztreonam-avibactam, particularly when multiple resistance mechanisms are present.