Comparative In-vitro Activity of Doripenem, Imipenem and Meropenem against Gram Negative Pathogens

This study compared the susceptibility of common Gram-negative bacilli causing serious infections in hospitalized patients with doripenem, imipenem and meropenem. Gram-negative isolates were collected from the Department of Microbiology, G B Pant Hospital and MICs of doripenem, imipenem and meropenem were determined using E test methodology. Susceptibility was interpreted according to CLSI 2015 guidelines. Out of 52 gram negative isolates tested, 26(50%) were Pseudomonas aeruginosa and 26(50%) were Enterobacteriacae of which 21% (11/52) were E. coli and 29% (15/52) were Klebsiella spp. The MIC range for all the clinical isolates was 0.125–32 ug/ml,.016-32 ug/ml and.008-32 ug/ml for imipenem, meropenem and doripenem respectively. The MIC 50/MIC₉₀ (MIC for 50% of the organisms/MIC for 90% of the organisms) for imipenem, meropenem and doripenem were 3/32 ug/ml, 2/32 ug/ml and 1.5/32 ug/ml respectively. For Pseudomonas aeruginosa the MIC₉₀ was lowest for meropenem (16 ug/ml) compared to both imipenem and doripenem (>32 ug/ml). For Enterobacteriacae MIC 90 was same for all three carbapenems (>32 ug/ml). Fifty four % (28/52) of the isolates were doripenem susceptible while imipenem and meropenem susceptibility was 42% (22/52) and 52% (27/52) for all clinical isolates. With high carbapenem resistance being reported worldwide especially imipenem and meropenem, doripenem should be reserved and used judiciously for the treatment of drug resistant gram negative infections.