International Board of Certified Lactation Consultant (IBCLC) Practice Exam

If a woman takes 80 mg of a drug with a half-life of 3 hours, how much will remain after 3 half-lives?

1. 5 mg

2. 10 mg

3. 20 mg

4. 30 mg

The correct answer is: 10 mg

To determine how much of the drug will remain in the body after three half-lives, it is essential to understand the concept of half-life. The half-life of a drug is the time it takes for the concentration of the drug in the bloodstream to reduce to half of its initial amount. Starting with an initial dose of 80 mg, we observe the following over three half-lives: 1. After the first half-life (3 hours), the amount remaining is half of 80 mg, which is 40 mg. 2. After the second half-life (another 3 hours, totaling 6 hours), the amount remaining will be half of 40 mg, which is 20 mg. 3. After the third half-life (another 3 hours, totaling 9 hours), the amount will be half of 20 mg, resulting in 10 mg. Thus, after three half-lives, 10 mg of the drug will remain in the body. This reasoning confirms that the correct answer reflects how drug concentration decreases over time with each half-life, providing clarity on pharmacokinetics and the behavior of medications in the body.