A patient with a drug Z half-life of 30 minutes and current plasma concentration of 200 mcg/mL asks how long to fall to 25 mcg/mL. How many minutes?

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Study for the Foundation Year Pharmacy – Clinical Practice Test. Prepare with detailed questions, step-by-step explanations, and test format insights. Enhance your readiness and confidence!

Multiple Choice

A patient with a drug Z half-life of 30 minutes and current plasma concentration of 200 mcg/mL asks how long to fall to 25 mcg/mL. How many minutes?

Explanation:
This tests understanding of first-order elimination and half-life. The drug’s concentration halves every 30 minutes. Starting at 200 mcg/mL: - after 30 minutes: 100 - after 60 minutes: 50 - after 90 minutes: 25 Three half-lives have passed, so it takes 90 minutes to fall from 200 to 25 mcg/mL. (You can also see this math via (1/2)^(t/30) = 25/200 = 1/8, which yields t = 90 minutes.)

This tests understanding of first-order elimination and half-life. The drug’s concentration halves every 30 minutes. Starting at 200 mcg/mL:

  • after 30 minutes: 100

  • after 60 minutes: 50

  • after 90 minutes: 25

Three half-lives have passed, so it takes 90 minutes to fall from 200 to 25 mcg/mL. (You can also see this math via (1/2)^(t/30) = 25/200 = 1/8, which yields t = 90 minutes.)

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