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Efficacy ratio: A tool to enhance optimal antimicrobial use for intra-abdominal infections

Priyanka Sabu1, Divyaa Elangovan1, Agila Kumari Pragasam1

  • 1Department of Clinical Microbiology, Christian Medical College, Vellore, Tamil Nadu, India.

Indian Journal of Pharmacology
|February 21, 2019
PubMed
Abstract

Insights

The efficacy ratio (ER) helps select the best antimicrobial for intra-abdominal infections by comparing minimum inhibitory concentration (MIC) values. This method aids in choosing effective treatments and tracking antimicrobial resistance development.

Area of Science:

  • Clinical microbiology
  • Infectious diseases
  • Pharmacology

Background:

  • Antimicrobial resistance (AMR) and suboptimal antibiotic regimens complicate intra-abdominal infection (IAI) treatment outcomes.
  • Minimum Inhibitory Concentration (MIC) values guide antimicrobial selection but are difficult to compare across different drugs due to varying breakpoints.
  • The efficacy ratio (ER) offers a standardized method to compare antimicrobial susceptibility by relating susceptible MIC breakpoints to isolate MICs.

Purpose of the Study:

  • To evaluate the utility of the efficacy ratio (ER) for selecting appropriate empiric antimicrobial therapy in intra-abdominal infections.
  • To compare the in vitro activity of various antibiotics against common Gram-negative pathogens causing IAIs using ER.

Main Methods:

  • A prospective observational study analyzed 356 *Escherichia coli* and 158 *Klebsiella* spp. isolates from IAIs.
  • Minimum Inhibitory Concentrations (MICs) were determined using the microbroth dilution method.
  • The efficacy ratio (ER) was calculated for each antibiotic against all collected isolates.

Main Results:

  • Ertapenem, amikacin, and piperacillin/tazobactam demonstrated superior activity within their respective antibiotic classes against both *E. coli* and *Klebsiella* spp. based on ER calculations.
  • The study identified specific antibiotics with favorable ERs, indicating higher susceptibility.
  • ER calculations provided a comparative measure of antibiotic effectiveness against the tested pathogens.

Conclusions:

  • The efficacy ratio (ER) is a novel approach for interpreting antimicrobial susceptibility reports to guide empiric treatment choices in IAIs.
  • ER has potential applications in determining the optimal use of susceptible drugs in monotherapy or combination therapy.
  • Tracking shifts in ER over time can monitor the development of antimicrobial resistance and rising MIC values.
Keywords:
AntimicrobialsGram-negative organismsefficacy ratioertapenemminimum inhibitory concentration

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