Efficacy Ratio Based Comparison of Susceptible Minimum Inhibitory Concentration of Antibiotics in E. coli Isolates of Bacteremia-A Retrospective Study
Author(s): Priya Venkatachalam*, Chitralekha Saikumar and Srivalsa Bhaskaran
Abstract
Introduction: It is necessary to compare the susceptible minimum inhibitory concentrations (MIC) of different antibiotics to choose the appropriate one. Direct comparison of MICs cannot be done since the breakpoints are different for each antibiotic. In this scenario Efficacy ratio(ER) of an antibiotic can be determined .This is the ratio between the susceptible breakpoint and the susceptible MIC of the specific antibiotic. The therapeutic efficacy is directly proportional to the ER value. ER is a significant factor in antimicrobial agent selection and a very useful tool in planning the empirical therapy. Aim: To calculate the Efficacy ratio of susceptible minimum inhibitory concentrations of antibiotics in E.coli isolates of bacteremia and select the appropriate antibiotic for treatment. Materials and methods: Retrospectively study the Vitek 2 derived susceptible minimum inhibitory concentrations of E.coli isolates from bacteremia and determines the Efficacy ratio. Result: Amikacin had the Highest ER 8 for 88% of isolates. Tigecycline (100%), colistin (97%), imipenem (94%), Meropenem (100%), Meropenem (100%), Gentamycin (88%), Piperacillin tazobactzm (97%) all had ER of 4. Cotrimoxazole (100%), Cefepime (92%), Cefoperazone sulbactam (91%) had ER of 2. Ertapenem (100%), Ceftriaxone (100%), Ciprofloxacin (100%), Amoxyclav (40%), Cefuraxime (92%), had ER of 1. Ampicillin ER was 1 and 4 with only 3 isolates in each category. Conclusion: Selecting the antibiotic based on MIC value is advantageous for positive treatment outcome and prevention of resistant subpopulation. The antibiotics with High degree of susceptibility are preferred for more effective treatment for which calculating ER value is of immense help and it is to be correlated with the type of infection, side effects, frequency of drug administration etc.