Question

For a drug that has an initial plasma concentration of 120 mg/L and a half-life of 3 hours, what would the plasma concentration be 12 hours after the initial concentration? A. 15 mg/L B. 112.5 C. 7.5 mg/L D. 60

Answer 1

To calculate the plasma concentration 12 hours after the initial concentration, we need to determine how many half-lives have passed during that time.

The half-life of the drug is given as 3 hours. Therefore, the number of half-lives in 12 hours can be calculated as follows:

Number of half-lives = (time elapsed) / (half-life)
Number of half-lives = 12 hours / 3 hours
Number of half-lives = 4

Each half-life reduces the concentration by half. Therefore, after 4 half-lives, the plasma concentration would be:

Plasma concentration = (initial concentration) / (2 ^ number of half-lives)
Plasma concentration = 120 mg/L / (2^4)
Plasma concentration = 120 mg/L / 16
Plasma concentration = 7.5 mg/L

Therefore, the plasma concentration 12 hours after the initial concentration would be 7.5 mg/L.

The correct answer is C. 7.5 mg/L.