Comparison of fixed concentration and fixed ratio options for testing susceptibility of gram-negative bacilli to piperacillin and piperacillin/tazobactam

  • M. A. Pfaller
  • A. L. Barry
  • P. C. Fuchs
  • E. H. Gerlach
  • D. J. Hardy
  • J. C. McLaughlin
Notes

Abstract

Piperacillin combined with tazobactam was tested at both a fixed ratio (8:1) and fixed tazobactam concentration (4 µg/ml) against 2,685 consecutively isolated gram-negative bacilli and 56 highly piperacillin-resistant isolates. Tazobactam significantly enhanced the spectrum of piperacillin activity. Overall, at a concentration of 16 μg/ml piperacillin alone inhibited 78.8 % of theEnterobacteriaceae isolates compared to inhibition of 92.7 % and 95.5 % by the 8:1 ratio and fixed (4 µg/ml) tazobactam combinations, respectively. In MIC tests the two combination options performed comparably against both routine and highly piperacillin-resistant isolates. Synergistic inhibition was observed for comparable numbers of isolates with the two combination options, the most marked effect being seen in the more highly piperacillin-resistant isolates. Both testing options are supported by the available human pharmacokinetic data; however the 8:1 ratio of piperacillin to tazobactam may be preferable given that the clinical formulation contains the two compounds in an 8:1 ratio and this ratio is maintained in vivo.

Keywords

Internal Medicine Testing Susceptibility Marked Effect Pharmacokinetic Data Piperacillin 

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Copyright information

© Friedr. Vieweg & Sohn Verlagsgesellschaft mbH 1992

Authors and Affiliations

  • M. A. Pfaller
    • 1
  • A. L. Barry
    • 2
  • P. C. Fuchs
    • 3
  • E. H. Gerlach
    • 4
  • D. J. Hardy
    • 5
  • J. C. McLaughlin
    • 6
  1. 1.Department of Pathology L471Oregon Health Sciences UniversityPortlandUSA
  2. 2.The Clinical Microbiology InstituteTualatinUSA
  3. 3.St. Vincent Hospital & Medical CenterPortlandUSA
  4. 4.St. Francis Regional Medical CenterWichitaUSA
  5. 5.University of Rochester Medical CenterRochesterUSA
  6. 6.University of New Mexico Medical CenterAlbuquerqueUSA

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