High-dose aztreonam potentiates the combined antimicrobial activity of ceftazidime-avibactam against extensively drug-resistant New Delhi metallo-β-lactamase positive Pseudomonas aeruginosa in severe pneumonia treatment: the first global case report.

Extensively drug-resistant Pseudomonas aeruginosa (XDR-PA) present increasing incidence and limited therapeutic options, emerging as one of the serious public health threats worldwide. Here, we report a case of an elderly male patient with multiple primary diseases who developed a severe pneumonia following long-term bedrest due to an accidental tumble after cerebral infarction. In the meantime, plenty of Gram-negative bacilli were repeatedly detected in his sputum and rapidly spread into his blood. This strain was ultimately identified as New Delhi metallo-β-lactamase (NDM) positive XDR-PA. Subsequently, the patient was treated with a combination of ceftazidime-avibactam (2.5 g q8h) and high-dose aztreonam (2 g q6h) under close supervision on his hepatorenal function. No dose adjustment was made throughout the treatment course. After one week of therapy, the patient's symptoms were remarkably resolved, and finally discharged. This is the first evidence worldwide of successful treatment for severe pneumonia caused by NDM positive XDR-PA using this dose-dependent combination therapeutic regimen as far as we know. The accurate and timely results of carbapenemase typing and combined antimicrobial susceptibility testing support our bold attempt at this novel treatment regimen, ultimately making the patient recover with a favorable prognosis.