A client has been started on diltiazem (Cardizem), a susbstrate of the cytochrome CYP3A4 isoenzyme system. The client also takes phenobarbital, an inducer of the CYP3A4 isoenzyme system, for seizures. What does the nurse recognize about diltiazem?
1. It will not be able to cross the blood brain barrier (BBB).
2. It will be metabolized by the kidneys.
3. It might be inactivated at a faster rate than normal.
4. It might be excreted at a slower rate.
Correct Answer: 3
Rationale 1: The cytochrome P460 enzyme system does not affect ability to cross the BBB. Lipid solubility of a drug determines the ability to cross the BBB.
Rationale 2: The drug will still be metabolized by the liver, not the kidneys.
Rationale 3: When one drug induces an enzyme system, it accelerates the metabolism of other drugs using the same isoenzyme substrate—in this case, the CYP3A4 system, which causes early inactivation of the drug.
Rationale 4: The drug will be metabolized faster and therefore excreted more quickly, not more slowly.
Global Rationale: When one drug induces an enzyme system, it accelerates the metabolism of other drugs using the same isoenzyme substrate—in this case, the CYP3A4 system, which causes early inactivation of the drug. The cytochrome P460 enzyme system does not affect ability to cross the BBB. Lipid solubility of a drug determines the ability to cross the BBB. The drug will still be metabolized by the liver, not the kidneys. The drug will be metabolized faster and therefore excreted more quickly, not more slowly.
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