A 29-year-old man presents to his primary care physician complaining of dysuria, urgency, and painful ejaculation. The patient has a past medical history of allergic rhinitis. Physical examination reveals a tender prostate. The patient is given a prescription of sulfa- methoxazole to be taken daily (q 12 h) for 30 days. The half-life is 12 h. How long will it take for the medication to reach 90% of its final steady state level? * (A) 10 h (B) 20h (C) 30 h (D) 48 h (E) 50h
Question
A 29-year-old man presents to his primary care physician complaining of dysuria, urgency, and painful ejaculation. The patient has a past medical history of allergic rhinitis. Physical examination reveals a tender prostate. The patient is given a prescription of sulfa- methoxazole to be taken daily (q 12 h) for 30 days. The half-life is 12 h. How long will it take for the medication to reach 90% of its final steady state level? * (A) 10 h (B) 20h (C) 30 h (D) 48 h (E) 50h
Solution
The time it takes for a drug to reach steady state is typically around 4-5 half-lives. In this case, the half-life of the drug is 12 hours. Therefore, it would take approximately 48-60 hours for the drug to reach steady state. However, the question asks for the time it would take for the drug to reach 90% of its final steady state level. This typically occurs around 3.3 half-lives. Therefore, we multiply 3.3 by the half-life of the drug:
3.3 * 12 hours = 39.6 hours
This is not an option in the multiple choice answers. The closest answer to this calculation is (D) 48 hours. Therefore, (D) 48 hours is the most appropriate answer.
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