# How to determine enzyme inhibitor efficacy?

At what percentage reduction or increase in Km and Vmax is an enzyme inhibitor regarded as effective?- is any percentage increase or reduction regarded as being a clinically useful level of inhibition, or would it have to be over a certain limit?

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If the inhibitor is a competitive inhibitor, to quantify inhibition the $K_m$ of the inhibitor ($K_I$) is determined.
$K_I$ is compared to the $K_m$ of the substrate.
$V_{max}$ is unaffected by a competitive inhibitor.
In the presence of an inhibitor the kinetics are modified such that the enzyme has an effect $K_m$ as:
$K_m(1 + [I]/K_I)$