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Pharmacology 13

A 68-year-old woman presents to the office for a routine follow-up visit. She presently does not have any complaints. She was diagnosed with atrial fibrillation 5 years ago. She denies any shortness of breath, palpitations, or chest pain. She is currently taking diltiazem and warfarin. Since last week, she has also started taking a liquid herbal extract of St John’s Wort daily to help her lose weight. Vital signs are temperature 36.4° C (97.5°°F), blood pressure 126/71 mmHg, pulse 89 beats/min, and respirations 16/min. Physical examination reveals no significant abnormalities.

Which of the following is the mechanism by which the herbal extract is most likely to interfere with the patient’s anticoagulant medication?

  • A) Competitive inhibition of the medication’s binding site
  • B) Decreasing intestinal absorption of the drug
  • C) Increasing hepatic metabolism of the medication
  • D) Increasing renal metabolism of the medication
  • E) Inhibiting enzymatic conversion of the drug to its active metabolite


Arihant Senthil


Dr. Ted O'Connell