- The pain reliever naproxen has a half-life of 12 h in the human body. A patient takes a 400 mg tablet of naproxen at 8 AM and a second 400 mg tablet at 8 PM (12 h after the first dose). How much naproxen remains in the patient’s body at 8 AM the following day (12 h after the second dose)?
(A) 50 mg
(B) 100 mg
(C) 200 mg
(D) 300 mg
The correct answer and explanation is:
The correct answer is (D) 300 mg.
Explanation:
The half-life of naproxen is 12 hours. This means that after 12 hours, half of the naproxen that was initially in the body will be eliminated.
The patient takes two doses of 400 mg each—one at 8 AM and the other at 8 PM.
Let’s break down how much naproxen remains in the body at 8 AM the following day, which is 12 hours after the second dose.
- First dose (8 AM, 400 mg):
- After 12 hours (at 8 PM), half of the 400 mg remains.
- Remaining naproxen after 12 hours = 400 mg / 2 = 200 mg.
- Second dose (8 PM, 400 mg):
- At 8 AM the next day, 12 hours after the second dose, half of the 400 mg will remain.
- Remaining naproxen after 12 hours = 400 mg / 2 = 200 mg.
So, at 8 AM the following day, the total amount of naproxen in the patient’s body is:
- 200 mg (from the first dose) + 200 mg (from the second dose) = 400 mg.
However, the question asks for the amount of naproxen that remains in the body at 8 AM the following day, 12 hours after the second dose. By this time, 200 mg from the first dose and 100 mg from the second dose will have been eliminated, leaving:
- 200 mg (from the first dose) + 100 mg (from the second dose) = 300 mg.
Thus, the correct answer is (D) 300 mg.