RH Herb-Drug Interaction Pharmacology 3 — Questions and Answers
Question 1: Which mechanism best describes a pharmacodynamic herb-drug interaction?
- Herb alters drug absorption by changing gastric pH
- Herb and drug produce additive or opposing effects at the same physiological target (Correct answer)
- Herb induces hepatic enzymes increasing drug clearance
- Herb chelates the drug in the GI tract reducing bioavailability
Correct answer: Herb and drug produce additive or opposing effects at the same physiological target
Pharmacodynamic interactions occur when herb and drug act on the same receptor, pathway, or physiological system, producing additive, synergistic, or antagonistic effects.
Question 2: A patient on SSRIs for depression also begins taking high-dose St. John's Wort. The most serious potential pharmacodynamic concern is:
- Reduced SSRI plasma levels causing depression relapse only
- Serotonin syndrome due to combined serotonergic activity (Correct answer)
- Hepatotoxicity from combined metabolism
- Sedation due to GABA potentiation
Correct answer: Serotonin syndrome due to combined serotonergic activity
St. John's Wort inhibits serotonin reuptake; combined with SSRIs, excess serotonergic activity can trigger life-threatening serotonin syndrome.
Question 3: Valerian and kava taken alongside benzodiazepines may cause excessive sedation. This is an example of:
- Pharmacokinetic antagonism
- Synergistic pharmacodynamic CNS depression (Correct answer)
- Enzyme induction reducing drug efficacy
- Receptor upregulation increasing sensitivity
Correct answer: Synergistic pharmacodynamic CNS depression
Valerian and kava both potentiate GABA activity, producing additive CNS depression when combined with benzodiazepines.
Question 4: Which herb most commonly interacts with antiplatelet drugs (e.g., aspirin, clopidogrel) via pharmacodynamic addition?
- Echinacea
- Ginger (Correct answer)
- Ashwagandha
- Marshmallow root
Correct answer: Ginger
Ginger contains gingerols that inhibit thromboxane synthesis and platelet aggregation, adding to antiplatelet drug effects and increasing bleeding risk.
Question 5: A patient on metformin for type 2 diabetes begins using berberine-containing herbs. The primary concern is:
- Reduced metformin absorption due to pH changes
- Additive blood glucose lowering causing hypoglycemia (Correct answer)
- CYP2D6 inhibition increasing metformin levels significantly
- Antagonism of metformin's insulin-sensitizing effect
Correct answer: Additive blood glucose lowering causing hypoglycemia
Berberine independently lowers blood glucose via AMPK activation and gut flora modulation, creating additive hypoglycemic risk with metformin.
Question 6: Licorice root (Glycyrrhiza glabra) can antagonize antihypertensive drugs through which mechanism?
- CYP3A4 induction reducing drug levels
- Sodium retention and potassium loss from pseudoaldosterone effect (Correct answer)
- Beta-receptor upregulation countering beta-blockers
- Direct vasoconstriction via histamine release
Correct answer: Sodium retention and potassium loss from pseudoaldosterone effect
Glycyrrhizin inhibits 11-beta-hydroxysteroid dehydrogenase, causing a pseudoaldosterone effect with sodium retention, potassium loss, and elevated blood pressure.
Question 7: When assessing herb-drug interactions, which factor most increases the clinical significance of an interaction?
- The herb being classified as 'natural'
- The drug having a narrow therapeutic index (Correct answer)
- The interaction being in vitro only
- The patient taking the herb only on weekends
Correct answer: The drug having a narrow therapeutic index
Drugs with narrow therapeutic indices (e.g., warfarin, digoxin, cyclosporine) have little margin between therapeutic and toxic levels, making small pharmacokinetic changes clinically dangerous.
RH Herb-Drug Interaction Pharmacology 3
Which mechanism best describes a pharmacodynamic herb-drug interaction?