StudentRDH Pharmacology Practice Exam

To determine the percentage of a drug remaining in the body after three half-lives, it is important to understand the concept of half-life itself. The half-life of a drug is the time it takes for the concentration of the drug in the bloodstream to reduce to half its original amount.

After one half-life, 50% of the drug remains. After the second half-life, the remaining 50% is again halved, leaving 25% of the original amount. Following the third half-life, the remaining amount is halved again, resulting in 12.5% of the original drug remaining in the body.

This breakdown can be summarized as follows:

- After 1 half-life: 50% remaining

- After 2 half-lives: 25% remaining

- After 3 half-lives: 12.5% remaining

Therefore, after three half-lives, 87.5% of the drug has been eliminated from the body, and only 12.5% remains. This calculation confirms that the correct response reflects the pharmacokinetic principle of drug clearance over time.