RH Herb-Drug Interaction Pharmacology 2

Question 1

Which CYP450 enzyme is most significantly induced by St. John's Wort, leading to reduced plasma levels of many drugs?

Accepted Answer

CYP3A4

Answer

St. John's Wort potently induces CYP3A4, which metabolizes roughly 50% of all drugs, causing therapeutic failure.

Question 2

A patient on cyclosporine for organ transplant begins taking St. John's Wort. What is the primary clinical concern?

Accepted Answer

Organ rejection due to subtherapeutic cyclosporine levels

Answer

St. John's Wort induces CYP3A4 and P-glycoprotein, dramatically lowering cyclosporine levels and risking acute organ rejection.

Question 3

Goldenseal (Hydrastis canadensis) inhibits which CYP450 enzyme, potentially increasing toxicity of drugs metabolized by it?

Accepted Answer

CYP2D6

Answer

Goldenseal's berberine and hydrastine inhibit CYP2D6, slowing metabolism of drugs like codeine, dextromethorphan, and some antidepressants.

Question 4

P-glycoprotein (P-gp) is an efflux transporter important in herb-drug interactions. Which herb is a known inducer of P-gp?

Accepted Answer

St. John's Wort

Answer

St. John's Wort induces P-gp efflux transport, reducing intestinal absorption and increasing renal/biliary elimination of substrate drugs.

Question 5

Which pharmacokinetic phase is primarily affected when a herb inhibits intestinal CYP3A4?

Accepted Answer

First-pass metabolism / absorption

Answer

Inhibiting intestinal CYP3A4 reduces first-pass metabolism, increasing oral bioavailability of substrate drugs.

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