The half-life of a drug is determined by which processes?

The half-life of a drug is determined by which processes?

• A. Metabolism and excretion
• B. Absorption only
• C. Distribution only
• D. Protein binding only

Answer: (A)

Half-life is the time it takes for the drug’s plasma concentration to fall by half, and that rate is set by how quickly the body eliminates the drug. The main elimination routes are metabolism (primarily in the liver) and excretion (primarily by the kidneys, and also via bile). Absorption affects how quickly the drug enters circulation, not how quickly it’s removed once in the body. Distribution describes how the drug moves into tissues and can shape the early concentration-time profile, but the rate-limiting step for elimination—the half-life—comes from clearance, which depends on metabolism and excretion. In simple terms, a drug’s half-life increases if metabolism or excretion slows (organ impairment, for example) and decreases if clearance speeds up.

Half-life is the time it takes for the drug’s plasma concentration to fall by half, and that rate is set by how quickly the body eliminates the drug. The main elimination routes are metabolism (primarily in the liver) and excretion (primarily by the kidneys, and also via bile). Absorption affects how quickly the drug enters circulation, not how quickly it’s removed once in the body. Distribution describes how the drug moves into tissues and can shape the early concentration-time profile, but the rate-limiting step for elimination—the half-life—comes from clearance, which depends on metabolism and excretion. In simple terms, a drug’s half-life increases if metabolism or excretion slows (organ impairment, for example) and decreases if clearance speeds up.