When antibiotics were first come into use they were successfully used in therapy since there was not yet any resistance problem. Worldwide multidrug resistance developed in pathogenic bacteria has a major therapeutic challenge. With rapidly increasing antibiotic resistance and insufficiencies in the development of new antimicrobial drugs, maintenance and preservation of the efficacy of currently available antibiotics have gained importance. Thus, new drug development studies or therapeutic strategies are needed to fight against antimicrobial resistance with batteries of drugs rather than individual drugs.

Antibiotic combination studies allow exploration of different molecular targets of individual agents and thereby broaden the spectrum of action. The synergistic effect of combinations occurs through inhibition of different targets through different mechanisms or by inhibiting targets in the same way or by inhibiting the same target in different ways. Combinations have distinct advantages including their synergistic effects, prevention of emergence of drug resistance, reduction of toxicity, and providing broad antimicrobial spectrum.

Antibiotic resistance is detected in many bacterial isolates in nature. Nowadays, there is a growing evidence that clinical resistance mechanisms are closely associated with mechanisms found in the environment.

In this review, the available data about antibiotic combinations with synergistic activities were evaluated.