Treatment of Urinary Tract Infections Caused by NDM-Producing Organisms
Introduction to Recommended Treatment
- The International Journal of Antimicrobial Agents recommends aztreonam combined with ceftazidime-avibactam as the preferred treatment for urinary tract infections caused by NDM-producing organisms, with a STRONG recommendation and MODERATE certainty of evidence 1, 2, 3
Rationale for Combination Therapy
- Aztreonam is stable against NDM and other metallo-β-lactamases because these enzymes cannot hydrolyze monobactam antibiotics, according to the International Journal of Antimicrobial Agents 1, 3
- The combination of aztreonam and ceftazidime-avibactam creates synergistic activity that restores full antimicrobial efficacy, as reported by the International Journal of Antimicrobial Agents and the Journal of Microbiology, Immunology and Infection 1, 3
Clinical Evidence
- Patients with bloodstream infections caused by NDM-producing Klebsiella pneumoniae who received ceftazidime-avibactam plus aztreonam had a 30-day mortality of 19.2% versus 44% in those receiving other active antibiotics, representing a 56% relative risk reduction in mortality, as found by the International Journal of Antimicrobial Agents and the Journal of Microbiology, Immunology and Infection 1, 2, 3
- The highest mortality rates were observed in patients who received colistin-containing regimens, making older alternatives significantly inferior, according to the International Journal of Antimicrobial Agents 1
Alternative Treatments
- Cefiderocol may be considered as an alternative with a CONDITIONAL recommendation and LOW certainty of evidence, achieving 75% clinical cure in MBL-producing CRE infections, as reported by the International Journal of Antimicrobial Agents and Praxis Medical Insights 1, 3
Critical Considerations
- Aztreonam monotherapy should never be used for NDM infections due to co-produced β-lactamases that inactivate aztreonam, as warned by the International Journal of Antimicrobial Agents and Praxis Medical Insights 1, 3
- Treatment should not be delayed waiting for carbapenemase typing—if NDM is suspected based on epidemiology or rapid testing, initiate ceftazidime-avibactam plus aztreonam immediately, as advised by the Journal of Microbiology, Immunology and Infection 2
- Colistin-based regimens should be avoided as first-line therapy due to significantly higher mortality compared to the aztreonam combination, as noted by the International Journal of Antimicrobial Agents 1
Treatment of Bacterial Strains Positive for NDM-1, CTX-M, and OXA-48 Genes
Understanding the Resistance Profile
- The International Society for Antimicrobial Chemotherapy recommends that NDM-1 (metallo-β-lactamase) hydrolyzes all β-lactams except aztreonam but cannot be inhibited by avibactam or vaborbactam 4
- OXA-48 (Class D carbapenemase) is inhibited by ceftazidime-avibactam, according to the International Society for Antimicrobial Chemotherapy 5
- CTX-M (ESBL) confers resistance to third-generation cephalosporins but is also covered by ceftazidime-avibactam, as stated by the International Society for Antimicrobial Chemotherapy 4
First-Line Treatment Regimen
- The Infectious Diseases Society of America recommends ceftazidime-avibactam 2.5g IV every 8 hours PLUS aztreonam 2g IV every 8 hours (adjust both for renal function) for the treatment of bacterial strains positive for NDM-1, CTX-M, and OXA-48 genes (STRONG recommendation, MODERATE certainty of evidence) 4
Critical Pitfalls to Avoid
- The European Society of Clinical Microbiology and Infectious Diseases advises against using aztreonam monotherapy for NDM infections—the co-produced CTX-M and other β-lactamases will inactivate it, leading to treatment failure 4
- The International Society for Antimicrobial Chemotherapy recommends not delaying treatment waiting for complete carbapenemase typing—if NDM is suspected based on epidemiology or rapid molecular testing, initiate ceftazidime-avibactam plus aztreonam immediately 5
- The Infectious Diseases Society of America recommends avoiding colistin-based regimens as first-line therapy due to significantly higher mortality compared to the aztreonam combination 4
- The European Society of Clinical Microbiology and Infectious Diseases advises against using ceftazidime-avibactam monotherapy for NDM producers—it has no activity against metallo-β-lactamases and will fail 4, 5
- The International Society for Antimicrobial Chemotherapy recommends not using meropenem-vaborbactam—it has no activity against either NDM-1 or OXA-48 5
Source Control
- The World Society of Emergency Surgery states that adequate source control is mandatory and complementary to antimicrobial therapy, including drainage of abscesses or infected collections, removal of infected devices or foreign bodies, and debridement of necrotic tissue 6
Treatment of OXA-48, NDM, and CTX-M Positive Infections
Introduction to Combination Therapy
- The Italian Society of Infection and Tropical Diseases recommends treating OXA-48, NDM, and CTX-M positive infections immediately with ceftazidime-avibactam 2.5g IV every 8 hours PLUS aztreonam 2g IV every 8 hours, as this combination is necessary to cover both the metallo-β-lactamase (NDM) and the serine carbapenemase (OXA-48) 7
Rationale for Combination Therapy
- NDM (metallo-β-lactamase) hydrolyzes all β-lactams except aztreonam, but aztreonam alone will fail because the co-produced CTX-M and other β-lactamases inactivate it, highlighting the need for combination therapy 7
- The synergistic mechanism of ceftazidime-avibactam and aztreonam works by ceftazidime-avibactam neutralizing the OXA-48 and CTX-M enzymes, while aztreonam remains stable against the NDM enzyme 7
Evidence Supporting the Recommended Regimen
- In patients with bloodstream infections caused by NDM-producing bacteria, those who received ceftazidime-avibactam plus aztreonam had a 30-day mortality of 19.2% versus 44% with other active antibiotics—a 56% relative risk reduction in mortality 7
- This recommendation carries a STRONG recommendation with MODERATE certainty of evidence from the Italian Society of Infection and Tropical Diseases and multiple international guidelines 7
Alternative Treatment Options
- Cefiderocol may be considered as an alternative with a CONDITIONAL recommendation and LOW certainty of evidence, achieving 75% clinical cure in MBL-producing infections 7
- However, concerns exist regarding higher MIC values against NDM producers, risk of treatment-emergent resistance, and unclear role of combination therapy 7
Aztreonam + Ceftazidime‑Avibactam for MBL‑Producing Acute Pyelonephritis in Severe β‑Lactam Allergy
Indication & Rationale
- For patients with severe β‑lactam allergy and acute pyelonephritis caused by metallo‑β‑lactamase (MBL)‑producing organisms, the recommended regimen is aztreonam 2 g IV every 8 h combined with ceftazidime‑avibactam 2.5 g IV every 8 h for 10–14 days, with renal‑function‑based dose adjustments. 8
- Aztreonam monotherapy is ineffective against MBL producers because these pathogens frequently co‑produce ESBL or AmpC β‑lactamases that hydrolyze aztreonam; avibactam neutralizes these co‑produced enzymes. 8
Efficacy & Outcomes
- In observational studies of bloodstream infections due to NDM‑producing organisms, the aztreonam‑ceftazidime‑avibactam combination reduced 30‑day mortality from 44 % to 19.2 % (56 % relative risk reduction) compared with other active regimens such as colistin‑based therapy. 8
- First‑line colistin‑based regimens are discouraged because they are associated with significantly higher mortality than the aztreonam‑ceftazidime‑avibactam combination. 8
Dosing & Pharmacodynamics
- Ceftazidime‑avibactam should be infused over 2 hours (2.5 g IV every 8 h) to maximize time‑above‑MIC, the critical pharmacodynamic parameter for both drugs. 8
Implementation Considerations
- Do not delay therapy while awaiting carbapenemase typing; if MBL production is suspected based on epidemiologic risk factors (e.g., recent travel to the Indian subcontinent or known local outbreaks) or rapid molecular testing, initiate aztreonam + ceftazidime‑avibactam immediately. 9
Alternative Options
- Cefiderocol may be considered as an alternative, achieving ≈ 75 % clinical cure in MBL‑producing carbapenem‑resistant Enterobacterales infections; however, this recommendation is conditional and supported by low‑certainty evidence. 8
Recommendation Strength
- The guideline issues a strong recommendation with moderate certainty of evidence for aztreonam plus ceftazidime‑avibactam as the preferred treatment of MBL‑producing infections, based on comparative observational data showing mortality benefit and endorsement by multiple international societies. [8][9]