Key words: Combination antibiotics, imepenem, multi drug resistant, Pseudomonas aeruginosa. Research Article Page: 27-34 Infections caused by MDR pathogens are a therapeutic challenge as they are resistant to most of the antibiotics used in clinical practice. Combination antimicrobial therapy usually involving a carbapenem is frequently considered as the last viable strategy to treat such infections. Often antibiotics in combination therapy are empirically selected on basis of intuition and

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... dotal reports. This study aims to determine in-vitro efficacy of antibiotic combinations devoid of carbapenems on MDR P. aeruginosa which will reveal the potential synergy between two antibiotics belonging to different chemical classes, especially when resistance to any one of them is present. Outcome of this study is expected to help in drafting healthy antibiotic policies and taking the pressure off carbepenems which are currently used overwhelmingly in clinical practice. This study was undertaken with the objective of studying the in-vitro effect of the following antibiotic combinations by chequer board assay: ceftazidime-amikacin, ceftazidime-ciprofloxacin, imepenem-amikacin and imepenem-ciprofloxacin, in 68 MDR clinical isolates of P. aeruginosa. CAZ-AMK and IMP-AMK combinations showed synergistic effect in 80%-90% of MDR isolates with FICI ≤0.5. Higher rates of indifference (0.5>FICI≤2) and antagonism (FICI>2) were observed with combinations involving fluroquinolones. This study proves that in vitro antimicrobial activity of antibiotic combinations having 3rd or 4th generation cephalosporin with aminoglycosides is comparable to that of imepenem tested alone or in combination. Therefore combinations devoid of carbepenems should be advocated to prolong the clinical usefulness of this antibiotic group.