Quadruple checkerboard : a modification of the three dimensional checkerboard for studying drugs combinations

Abstract

Antibacterial resistance caused by the misuse and overuse of antibacterial drugs resulted in a crisis that needs to be solved. Antibiotic combination is one of the solutions that can help in decreasing and controlling the development of resistance. The concept of combining drugs as a treatment for several diseases showed good results and promising control in the use of these drugs. However, combining drugs should be tested to see the effect of the combination and decide whether it can be used as a treatment. The first step is to test it in vitro. For this purpose, several methods have been developed like the checkerboard method, time kill curve assay, and many other methods. Each method has its advantages and disadvantages characterizing it from other methods. Checkerboard technique is used to test combination between 2 drugs. It has been developed to study combination between 3 drugs and was named three-dimensional checkerboard. The aim of this study is to develop the three-dimensional checkerboard into a technique that can test combination between 4 drugs. The developed technique was named Quadruple Checkerboard. In order to validate the developed technique, 2 trials where performed. In each trial 2 sets of experiments where performed. The first set included the Q-checkerboard technique between cefotaxime, amikacin, levofloxacin, and trimethoprim sulfamethoxazole, 3Dcheckerboard between cefotaxime, amikacin, and levofloxacin and the normal Checkerboard between cefotaxime and amikacin. The second set of experiments was done by another method used to study combination which is the time kill curve assay. The results obtained by the 2 methods were compared together and a percentage of agreement was calculated. The results showed an agreement of 66.66%. This percentage falls in the range of agreement mentioned in literature (44%-88%). The FIC was set to be 1 as the indifferent value and every FIC lower than 1 shows synergism and higher than 1 shows non-synergism.