Half-life describes the rate at which a drug disappears from the body through which processes?

Half-life describes the rate at which a drug disappears from the body through which processes?

• A. Metabolism, excretion or both
• B. Absorption only
• C. Tissue distribution only
• D. CNS penetration only

Answer: (A)

Half-life is about how long it takes for the drug’s concentration in the body to fall by half as the body eliminates it. The elimination processes that drive this decline are metabolism (usually in the liver) and excretion (kidneys, biliary system, etc.). Absorption affects how quickly the drug gets into circulation, not how quickly it’s removed, so it doesn’t determine the half-life. Tissue distribution can influence how the drug spreads and may cause an initial distribution phase, but the long-term reduction in concentration is governed by metabolism and excretion. Therefore, half-life reflects the rate at which the drug disappears from the body through metabolism, excretion, or both.

Half-life is about how long it takes for the drug’s concentration in the body to fall by half as the body eliminates it. The elimination processes that drive this decline are metabolism (usually in the liver) and excretion (kidneys, biliary system, etc.). Absorption affects how quickly the drug gets into circulation, not how quickly it’s removed, so it doesn’t determine the half-life. Tissue distribution can influence how the drug spreads and may cause an initial distribution phase, but the long-term reduction in concentration is governed by metabolism and excretion. Therefore, half-life reflects the rate at which the drug disappears from the body through metabolism, excretion, or both.