The Michaelis-Menten equation is shown below depicting the relationship between the rate of elimination of the drug and its concentration.

If the plasma's concentration is expessed in µg/ml and time in hours, the units are:

Vmax    (µg/ml)/h

Km          µg/ml

Vmax = maximum velocity of the enzyme process; the velocity may approach Vmax but will never reach it.

Km = Michaelis-Menten constant, equal to the concentration at which the rate of the process equals half of the maximum rate.

dS/dt = elimination rate of the substrate

dP/dt = rate of product formation

S = substrate