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A drug is started on Monday at 14:00 hours. It has a half-life of 8 hours and is dosed twice daily. What is a reasonable time to order a steady-state drug level?

A. Tuesday at 14:00 hours
B. Tuesday at 22:00 hours
C. Wednesday at 14:00 hours
D. Wednesday at 22:00 hours

Answer :

Final answer:

A reasonable time to measure the steady-state level of a drug with an 8-hour half-life, dosed twice daily, is after 4 to 5 half-lives have passed, making Wednesday at 14:00 hours the most appropriate time.

Explanation:

When considering the appropriate time to measure the steady-state level of a drug with an 8-hour half-life that is dosed twice daily, one must account for the time it takes to reach steady state. Typically, steady state is achieved after approximately 4 to 5 half-lives. In this scenario, the drug was started on Monday at 14:00 hours, and given the drug's half-life, a reasonable time to order a steady-state drug level would be after at least 4 to 5 half-lives have passed. This would put the reasonable time to measure the steady state around Wednesday at 14:00 hours (Option c), after 48 hours (6 half-lives) have elapsed.