Question

The dose of the drug is repeated at half-life intervals. After how many intervals the steady state (plateau) plasma drug concentration is reached?

• A. \( 2-3 \text{ half lives} \)
• B. \( 4-5 \text{ half lives} \)
• C. \( 6-7 \text{ half lives} \)
• D. \( 8-10 \text{ half lives} \)

Hint:

Remember the rule of thumb: it takes around 4-5 half-lives to reach steady state with regular dosing, regardless of the dose or the dosing interval (as long as it's consistent).

Answer 1

The Correct Option is B

When a drug is administered repeatedly at regular intervals, it takes approximately 4-5 elimination half-lives to reach steady-state plasma drug concentration. At steady state, the rate of drug administration equals the rate of drug elimination, and the plasma concentration fluctuates around an average value. While some accumulation occurs with each dose, it takes about 4-5 half-lives for this accumulation to plateau, reaching approximately 94-97% of the final steady-state concentration. The dosing interval being equal to the half-life is a common scenario for achieving and maintaining therapeutic concentrations.