FPGEE FPGEE Exam 2 — Questions and Answers
Question 1: Which cytochrome P450 enzyme is primarily responsible for the metabolism of warfarin's S-enantiomer?
- CYP3A4
- CYP2C9 (Correct answer)
- CYP2D6
- CYP1A2
Correct answer: CYP2C9
CYP2C9 metabolizes the more pharmacologically active S-warfarin, which is why CYP2C9 polymorphisms and inhibitors significantly affect warfarin dosing.
Question 2: A patient with CrCl of 25 mL/min requires anticoagulation. Which agent would be MOST appropriate to avoid with severe renal impairment?
- Warfarin
- Apixaban
- Dabigatran (Correct answer)
- Argatroban
Correct answer: Dabigatran
Dabigatran is approximately 80% renally excreted and is contraindicated in severe renal impairment (CrCl <15 mL/min) and requires dose adjustment at lower CrCl values.
Question 3: Which pharmacokinetic parameter describes the fraction of an administered drug dose that reaches systemic circulation unchanged?
- Volume of distribution
- Clearance
- Bioavailability (Correct answer)
- Half-life
Correct answer: Bioavailability
Bioavailability (F) represents the fraction of the administered dose that reaches the systemic circulation in active form, accounting for absorption and first-pass metabolism.
Question 4: A patient taking rifampin for tuberculosis starts oral contraceptives. What counseling is MOST important?
- Take the pill at a different time of day than rifampin
- Use additional barrier contraception because rifampin is a strong CYP inducer (Correct answer)
- Increase the estrogen dose to 50 mcg
- Switch to a progestin-only pill to avoid the interaction
Correct answer: Use additional barrier contraception because rifampin is a strong CYP inducer
Rifampin is a potent CYP3A4 inducer that significantly increases the metabolism of oral contraceptive hormones, reducing their efficacy and requiring additional contraception.
Question 5: Which buffer system is the PRIMARY extracellular buffer in human blood?
- Phosphate buffer system
- Protein buffer system
- Bicarbonate-carbonic acid system (Correct answer)
- Hemoglobin buffer system
Correct answer: Bicarbonate-carbonic acid system
The bicarbonate-carbonic acid buffer system is the primary extracellular buffer, accounting for about 80% of the total blood buffering capacity.
Question 6: A pharmacist receives a prescription for metformin 1000 mg twice daily. Which lab value is MOST critical to check before dispensing?
- Fasting blood glucose
- HbA1c
- Serum creatinine/eGFR (Correct answer)
- Liver function tests
Correct answer: Serum creatinine/eGFR
Metformin is contraindicated in patients with eGFR <30 mL/min/1.73m² due to risk of lactic acidosis from drug accumulation in renal impairment.
Question 7: What is the mechanism of action of proton pump inhibitors (PPIs)?
- Competitive antagonism of H2 receptors on parietal cells
- Irreversible inhibition of H+/K+-ATPase enzyme (Correct answer)
- Neutralization of gastric acid
- Stimulation of mucus secretion in the stomach
Correct answer: Irreversible inhibition of H+/K+-ATPase enzyme
PPIs irreversibly inhibit the H+/K+-ATPase (proton pump) on parietal cells, blocking the final step of acid secretion regardless of the stimulus.
FPGEE FPGEE Exam 2
Which cytochrome P450 enzyme is primarily responsible for the metabolism of warfarin's S-enantiomer?