What term denotes the time required for the amount of drug in the blood to be reduced by half?

What term denotes the time required for the amount of drug in the blood to be reduced by half?

• A. Half-life
• B. Bioavailability
• C. Volume of distribution
• D. Bioequivalence

Answer: (B)

Half-life is the time required for the amount of drug in the body (or in the blood) to decrease by half. This measure reflects how quickly the body eliminates the drug. In typical first-order kinetics, the concentration falls exponentially, so after one half-life it's halved, after two it's a quarter, and so on. The half-life is linked to clearance and volume of distribution by the equation t1/2 ≈ 0.693 × Vd / CL, and it remains constant for a given drug under linear kinetics, making it useful for predicting dosing intervals and time to reach steady state. Bioavailability describes how much of the administered dose reaches systemic circulation, not the rate of elimination. Volume of distribution is a theoretical volume that relates amount of drug in the body to plasma concentration, not a time measure. Bioequivalence compares two products’ absorption characteristics, not the elimination timing.

Half-life is the time required for the amount of drug in the body (or in the blood) to decrease by half. This measure reflects how quickly the body eliminates the drug. In typical first-order kinetics, the concentration falls exponentially, so after one half-life it's halved, after two it's a quarter, and so on. The half-life is linked to clearance and volume of distribution by the equation t1/2 ≈ 0.693 × Vd / CL, and it remains constant for a given drug under linear kinetics, making it useful for predicting dosing intervals and time to reach steady state.

Bioavailability describes how much of the administered dose reaches systemic circulation, not the rate of elimination. Volume of distribution is a theoretical volume that relates amount of drug in the body to plasma concentration, not a time measure. Bioequivalence compares two products’ absorption characteristics, not the elimination timing.