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? 




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.


Then, the degree of inhibition is a function the inhibitor and substrate concentrations.


$V\_{max}$ 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:


$K\_m(1 + [I]/K\_I)$


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