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. 2015 Sep 1;6:181. doi: 10.3389/fphar.2015.00181

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Copyright © 2015 Tang, Wennerberg and Aittokallio.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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The proposed terminology for classifying drug interactions. Using the interaction barometer allows a direct comparison between different drug combinations in terms of their degrees of interaction as well as their combination responses. If the observed drug combination effect y_c is lower than the maximum single drug effect max(y₁, y₂) but higher than the minimum effect min(y₁, y₂), then the combination is called weak antagonism; if y_c < min(y₁, y₂) it is called strong antagonism. To classify synergy, we consider the Bliss and Loewe models, with the expected effects denoted as y_BLISS and y_LOEWE, respectively. If max(y₁, y₂) < y_c < min(y_BLISS, y_LOEWE), then we call the combination as non-interaction; if y_HSA < y_c < min(y_BLISS, y_LOEWE) it is called weak synergy, and for y_c > max(y_BLISS, y_LOEWE) strong synergy.