Mixture dynamics: dual action of inhibition and stimulation.

The impact of a drug, or of multiple drugs, on different receptors usually results in a combination of responses. They may be either opposing or reinforcing one another and can lead to complex response versus drug-concentration relations. In this paper, complexity and synergy of multiple drug actions are studied on the basis of four data sets: two involving opposing actions and two resulting from synergistic actions. It is shown that turnover models can be successfully fitted to these data, offer a mechanism for dissecting complex response versus drug-concentration curves, for understanding and quantifying amplification of dual drug actions and elucidate the role of potencies and other parameters related to the different drugs.