CNS Pharmacology USMLE Step 1 Practice Question
A 44-year-old man with newly diagnosed atrial fibrillation starts flecainide 100 mg twice daily. His physician explains that reaching steady state requires approximately 5 half-lives, noting that flecainide has a volume of distribution of roughly 8–10 L/kg and undergoes hepatic metabolism with renal excretion. Vital signs: BP 138/82, HR 102, RR 16, Temp 37°C, SpO2 98%. ECG shows prolonged QRS duration. Creatinine clearance is 85 mL/min. The patient, currently taking no other medications, asks which factors primarily determine this drug's half-life. Which of the following best answers his question?
Answer choices
- AIt increases with greater potency and decreases with lower efficacy
- BIt is unrelated to renal or hepatic dysfunction
- CIt is determined only by receptor affinity
- DIt increases with larger volume of distribution and decreases with higher clearanceCorrect answer
- EIt depends only on hepatic first-pass metabolism
- FIt is directly proportional to the drug's lipophilicity and inversely proportional to plasma protein binding
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