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Drug synergism study

PA Pritha Agarwalla
RB Rajkumar Banerjee
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Isobologram analysis was done to study drug synergism. The isobologram was plotted as a graph of equally effective drug dose pairs (isoboles) into a single effect level. Selectively, a particular inhibitory concentrations of drug B and drug A (each alone) are chosen (here, 90% of the maximum (IC90)), resulting doses of combination effect are plotted as axial points in a Cartesian plot. The antagonistic, additive, and synergistic effects can be evaluated by calculating combination index (CI-value) using mathematical formula from isobologram. Formula and significance of CI-value is given below. Herein, ICx,A and ICx,B are the inhibitory concentration × (ICx) of drug A and drug B. The points of ICx of A and B were added by a straight line. The points at which concentrations of drug A and B meet is called as combination index (CI), which was calculated using this equation.

CI = CA, X/ICx, A + CB, X/ICx,B

Here, CI < 1 indicates synergism effect, CI = 1 indicates additive effect, CI > 1 indicates antagonism effect

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