CNS Pharmacology USMLE Step 1 Practice Question
A 65-year-old man with hypertension (BP 158/92 mmHg, HR 78) begins once-daily oral antihypertensive therapy. He asks when the medication will stabilize at near-constant average plasma concentration with consistent dosing. Laboratory studies show normal renal function (creatinine 0.9 mg/dL). He denies previous antihypertensive use. Assuming first-order elimination kinetics and no loading dose, after how many half-lives will steady-state plasma concentration be approached?
Answer choices
- AImmediately after the first dose because oral drugs bypass distribution
- BAfter one half-life regardless of clearance
- CAfter about 4 to 5 half-livesCorrect answer
- DAfter one dosing interval
- EOnly after receptor upregulation occurs
- FAfter about 2 to 3 half-lives, since steady state is achieved when cumulative drug equals twice the single-dose amount
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