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Updated: Jun 17, 2026

Quadruple-Checkerboard: A Modification of the Three-Dimensional Checkerboard for Studying Drug Combinations
Published on: July 24, 2021
Comparison of methods for evaluating drug-drug interaction
Liang Zhao1, Jessie L-S Au, M Guillaume Wientjes
1College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA.
Comparing drug-drug interaction analysis methods, this study found that curve shift, isobologram, combination index, and universal surface response analyses offer complementary insights into drug synergy and antagonism. Each method provides unique data for evaluating combination therapies.
Area of Science:
- Pharmacology
- Biostatistics
Background:
- Drug-drug interactions (DDIs) are critical in pharmacology.
- Accurate analysis of DDIs is essential for drug development and clinical practice.
Purpose of the Study:
- To compare the utility of four distinct methods for analyzing drug-drug interaction data.
- To evaluate these methods using published cytotoxicity data of anti-folate agent combinations.
Main Methods:
- Curve-shift analysis for visual inspection and parallelism evaluation.
- Isobologram analysis for identifying synergistic concentration ratios.
- Combination index analysis for quantitative synergy/antagonism estimation.
- Universal surface response analysis for summarizing interactions in a single parameter.
Main Results:
- Curve shift analysis allows visual assessment of dose-response curves.
- Isobolograms reveal concentration ranges for maximal synergy.
- Combination index provides quantitative synergy/antagonism measures.
- Universal surface response simplifies comparison of multiple drug combinations.
- Curve shift and universal surface response methods offer statistical differentiation of synergy, additivity, and antagonism.
Conclusions:
- Curve shift analysis, isobolograms, combination index, and universal response surface methods are valuable tools for DDI analysis.
- These methods provide complementary information, aiding comprehensive understanding of drug interactions.
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