DRUG METABOLISM FOR PHYSICIAN ASSISTANT STUDENTS

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DRUG METABOLISM FOR PHYSICIAN ASSISTANT STUDENTS
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VELOCITY OF METABOLISM OF A DRUG (1)
D\summer1\Kmx1.pzm
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VELOCITY OF METABOLISM OF A DRUG (2)
Kmx2.pzm
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FIRST ORDER METABOLISM
A drug may be given in doses that produce blood
concentrations less than the Km of the enyzme for
the drug.
v Vmax C Km C
When Km gtgtgt C,
and v ? C
then v Vmax C ,
Km
Metabolism of the drug is a first order process.
A constant fraction of the remaining drug is
metabolized per unit time. Most drugs are given
at concentrations smaller than the Km of the
enzymes of their metabolism.
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ZERO ORDER METABOLISM
A drug may be given in doses that produce blood
concentrations greater than the Km of the enyzme
for the drug.
v Vmax C K m C
When C gtgtgt Km,
then v Vmax C ,
C
and v Vmax
Metabolism of the drug is a zero order process. A
constant amount of the remaining drug is
metabolized per unit time. Phenytoin undergoes
zero order metabolism at the doses given.
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METABOLISM OF THREE DRUGS BY THE SAME ENZYME

• For which drug does the enzyme has the greatest
  affinity? What is the Vmax of the reactions?

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ADDITIONAL PHASE I REACTIONS
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ACETAMINOPHEN AND ITS PHASE II METABOLITES
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ACETAMINOPHEN AND ITS PHASE I METABOLITES
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AN ENZYME WITH DIFFERENT AFFINITIES FOR ITS
SUBSTRATES

• Using the graph above, determine the Km of the
  enzyme for each drug. Determine the Vmaxs.

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METABOLISM OF TWO DRUGS BY THE SAME ENZYME

• Discuss how drug A affects the metabolism of drug
  B when blood concentration of each is 40 mM.

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