If a drug reaches tissue equilibrium one hour after administration and its plasma level decreases by one-half between hours 2 through 5 after administration, its half-life would be ________ hours.

Question

Quizplus · Accepted Answer

If the plasma level decreases by one-half between hours 2 through 5 after administration, it means there are multiple half-lives during that time frame.

Let's say the initial concentration is 100 units.

At hour 2, the concentration would be 50 units (one half-life).

At hour 3, the concentration would be 25 units (two half-lives).

At hour 4, the concentration would be 12.5 units (three half-lives).

At hour 5, the concentration would be 6.25 units (four half-lives).

Since it takes one hour after administration to reach tissue equilibrium, the concentration at hour 1 would be 100 units.

Therefore, the total time for four half-lives is 5 hours (2+1+1+1), and each half-life would be 5/4 = 1.25 hours.

So the answer is option C, 3 hours is the half-life of this drug.

If a Drug Reaches Tissue Equilibrium One Hour After Administration