 This is because reversible competitive antagonists are surmountable antagonists.The magnitude of the rightward shift can be quantified with the dose ratio, r. The dose ratio r is the ratio of the dose of agonist required for half maximal response with the antagonist formula_1 present divided by the agonist required for half maximal response without antagonist ("control").In other words, the ratio of the EC50s of the inhibited and un-inhibited curves.