PK exam 2: drug elimin and hepatic CL: Enzyme kinetics

Drug metabolism and excretion processes are assumed to follow ____

• zero order

• first order

The reason most drugs display first order elimination is most drugs are presented to the metabolizing enzymes at conc. well below the enzymes max capacity.

• True

• False

Answer explanation

enzyme availability is not an issue therefore the rate of drug metab will only depend on conc. of the drug

Although most drugs follow first order kinetics, at higher plasma drug concentrations, these drug metabolizing enzymes have limited capacity and saturate.

• True

• False

When enzymes are saturated, drug elimination by metabolism occurs at a constant max rate which is ___

• first order

• zero order

The rate of drug elimination by metabolism depends on

• drug concentration

• enzyme concentration

Answer explanation

non-linear Michaelis-Menten kinetic equation

Michaelis menten equation assumes the rate of an enzymatic reaction is dependent on ___

• concentration of drug

• concentration of enzyme

When the drug concentration is < enzyme concentration, rate of metabolism is ___

• first order

• zero order

When drug concentration is > enzyme concentration, the rate of metabolism is ____

• first order

• zero order

Answer explanation

all enzymes are occupied and saturated = zero order

V=Vmax *[D]/KM + [D}

• Michaelis-Menton kinetic equation

• not this

V = Vmax * [D] / Km + [D]

V= __

• velocity of forward reaction

• max rate of metabolism

• michaelis constant