Synergistic Antibacterial Activity of Ceftriaxone–Clavulanic Acid and Ceftazidime–Clavulanic Acid Combinations Against Selected Bacterial Pathogens

Abstract

Combination therapy using a β-lactam antibiotic and a β-lactamase inhibitor may enhance effectiveness against resistant bacteria. This study examined the pharmacology and potential synergism of ceftriaxone-clavulanic acid and ceftazidime-clavulanic acid against Escherichia coli and Pseudomonas aeruginosa.

Antibacterial efficacy was evaluated using the disk diffusion method across 32 Petri dishes — 16 per bacterial strain. Each strain's dishes were divided equally among four treatments: ceftriaxone (CX), ceftriaxone-clavulanate (CXC), ceftazidime (CT), and ceftazidime-clavulanate (CTX). Plates were incubated at 37°C for 18–24 hours, then assessed for zones of bacterial inhibition.

Against E. coli, ceftriaxone alone showed greater activity than ceftazidime alone (mean: 12.5 vs. 1.75). Clavulanic acid enhanced both, with ceftazidime-clavulanate achieving the highest inhibition (mean = 20). Both combinations proved equally effective overall. Against P. aeruginosa, ceftriaxone again outperformed ceftazidime alone (mean: 17.25 vs. 4.00). Clavulanic acid did not significantly enhance ceftriaxone, but dramatically potentiated ceftazidime (mean: 4.00 to 21.5). Both clavulanate combinations were equally effective against this strain as well.

These findings reinforce the value of β-lactam/β-lactamase inhibitor combination therapy for infections caused by E. coli and P. aeruginosa. Despite differences in standalone potency, clavulanic acid effectively equalized the performance of both antibiotics, highlighting the importance of synergy testing in guiding optimal antibiotic treatment.