Methods: An Excel-based model to construct combination antibiograms was developed to assist clinicians in evaluating institutional susceptibility data. The University of Florida Health Shands Hospital microbiology laboratory supplied susceptibility data for ceftriaxone (CFX), cefepime (CEF), ciprofloxacin (CIP), and amikacin (AMI) to assess % gain achieved with combinations for E.coli (Ec) all blood isolates (n=206) and blood isolates with an ESBL phenotype (n=35). The same laboratory provided susceptibility data for CEF, piperacillin-tazobactam (PTZ), AMI and CIP for P.aeruginosa (Pa) (all, n=250; carbapenem-resistant (CARB-R), n=30).
Results: Percent gains achieved by adding AMI or CIP to CFX and CEF to capture at least one agent exhibiting in vitro susceptibility against all blood Ec were calculated: CFX-AMI, 16%; CFTX-CIP, 3%; CEF-AMI, 10%; CEF-CIP, 1%. The % gain specific to Ec blood isolates with an ESBL phenotype ranged from 9% to 86%. The combination with the greatest percent loss against blood Ec isolates, comparing all blood isolates to those with an ESBL phenotype, was CFX-CIP (∆-66%).
Percent gain achieved against all isolates of Pa by adding AMI or CIP to PTZ and CEF were CEF-AMI, 8%; CEF-CIP, 5%; PTZ-AMI, 15%; PTZ-CIP, 9%; percent gain of the same combinations against Pa CARB-R isolates were 23%, 10%, 47%, and 30%. respectively. Adding AMI to either beta-lactam: PTZ % S increased from 47% to 77% (+CIP) and to 94% (+AMI); CEF % S increased from 60% S to 70% (+CIP) and to 83% (+AMI).
Conclusion: Combination antibiogram models can assist clinicians in identifying regimens which may provide improved targeting of MDR phenotypes through calculation of percent gain.
M. Redell, Melinta Therapeutics, Inc.: Employee and Shareholder , Salary .
M. Balogh, Melinta Therapeutics, Inc.: Employee and Shareholder , Salary .
J. Massey, Melinta Therapeutics, Inc.: Employee and Shareholder , Salary .
M. Dudley, The Medicines Company: Employee , Salary .
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