Define half-life and describe how it influences dosing interval and steady-state concentration.

• A. Half-life is the time for plasma concentration to fall by 50%; dosing often follows half-life to maintain steady-state; steady-state occurs after about 4–5 half-lives.
• B. Half-life is the time to reach maximum concentration; steady-state occurs after 1 half-life.
• C. Half-life is the time for concentration to fall by 90%; steady-state occurs after 2 half-lives.
• D. Half-life is the time to excrete half of drug; dosing intervals are fixed and not related to half-life.

Answer: (A)