Combination agent antibiogram of common antimicrobial classes viz β-lactam drugs, aminoglycosides, fluoroquinolones and folate antagonist for major gram-negative pathogens—an innovative approach to assist appropriate empirical decisions

Prescribers have a tendency to empirically start on combination antimicrobial regimens instead of monotherapy in scenarios such as hemodynamically unstable or critically sick patients. However, most of these choices are based on their own experience and not evidence based. In our study, we have developed combination agent antibiogram for major gram-negative pathogens to assist appropriate empirical decisions. During the period January-December, 2023, susceptibility data of blood culture isolates were collated to develop combination antibiogram using the standard CLSI M39 guideline for five major gram-negative pathogens—, , , complex and Pseudomonas aeruginosa. The individual susceptibility profiles of the five gram-negative organisms and their aggregate was used generate antibiogram. The combination regimens chosen for developing combination antibiogram comprised of agents belonging to two different antimicrobial classes- β-lactams, quinolones, aminoglycosides or folate antagonist. The S% to combination agents was calculated as percentage of isolates susceptible to either of the antimicrobial agents. Results: Many combination regimens were found to demonstrate statistically significant improvement in susceptibility (S)% compared to the that of individual antimicrobial agent for and gram-negative bacilli level, to some extent for , but such finding was not observed for , or E. cloacae. Combination agent antibiogram for empirical choice is an excellent tool to provide evidence-based recommendations on selecting correct combination of antimicrobial agents as empirical choices. Every healthcare facility should prepare combination agent Antibiogram for the most commonly used antimicrobial combination regimens after discussion with the prescribers.