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USMLE · Question #434
USMLE Question #434: Real Exam Question with Answer & Explanation
The correct answer is D. 12 hours. The rule of thumb is that the plasma concentration will reach 50% in one half-life, 75% in two half- lives, 87.5% in three half-lives, etc., so that the difference between the current drug level and 100% halves with each half-life. In this instance, it takes two half-lives to rea
Question
A new antifungal medication is being tested in Phase I clinical trials. Examination of the pharmacokinetic properties of the drug reveals that the half-life of the drug is 6 hours. If a continuous intravenous infusion of this drug were started on a research subject, how long would it take to reach 75% of steady state?
Options
- A3 hours
- B6 hours
- C9 hours
- D12 hours
- E18 hours
- F24 hours
Explanation
The rule of thumb is that the plasma concentration will reach 50% in one half-life, 75% in two half- lives, 87.5% in three half-lives, etc., so that the difference between the current drug level and 100% halves with each half-life. In this instance, it takes two half-lives to reach 75%. The half-live of this drug is 6 hours, so two half-lives is 12 hours.
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