Carbapenem resistant gram-negative bacteria defined as gram negative organisms tested resistant to at least one of the carbapenem antibiotics i.e., meropenem, imipenem, doripenem or producing a carbapenemase. Infection with CR organisms Increases length of hospital stay and increases the mortality as well as higher direct and indirect healthcare costs. Carbapenemase producing bacteria is responsible for increased mortality with inappropriate antibiotic therapy. In a Prospective multi center observational study 30-day Mortality benefit ceftazidime avibactam (n=38) vs  colistin (n=99) observed as 9% vs 32%, Colistin group had more renal failure 5% vs 24% compared to ceftazidime Avibactam group. They  concluded that Ceftazidime avibactam may be reasonable alternative to colistin for KPC producing CRE infections. However, they included only KPC producing organisms, NDM and OXA 48 producing organisms are common in Indian population. Another prospective multicenter study done by Marco Falcone et al found ceftazidime avibactam and aztreonam(n=52) vs other active antibiotics combinations(n=50) had lower mortality 19.2 vs 44% for treating MBL producing Enterobacteriaceae and drug induced AKI was 1.9 in CFZ AVI AZT group vs 20% among colistin based regimens. Mortality in this group of patients may not be solely attributed to infection because of the underlying severity of primary disease. Clinical response in terms of the decreased need for vasopressors, liberation from mechanical ventilation ,renal replacement free days after initiation of antibiotic which are initiated due to sepsis could be better predictors in these circumstances.

 The present study is designed to observe clinical response as well as mortality benefit and microbiological response in patients treated with or going to treat with ceftazidime avibactam with or without aztreonam compared to other active antibiotics in carbapenem resistance gram negative bacterial infections. This study will be pure observational study, choice of antibiotic depends on treating consultant.