What measures the elimination of drugs from the body?

Half-life is the correct measure of how quickly a drug is eliminated from the body. It is defined as the time it takes for the concentration of the drug in the bloodstream to be reduced by half. This concept is crucial in pharmacology because it helps determine dosing schedules and how long a drug will remain effective in the body. The half-life can be influenced by various factors including the drug's properties, the patient's metabolism, and the method of elimination, typically through the liver or kidneys.

Other measures, such as circulatory rate, bioavailability, and therapeutic index, focus on different aspects of drug pharmacokinetics and pharmacodynamics. Circulatory rate relates to blood flow but does not directly measure drug elimination. Bioavailability describes the proportion of a drug that enters systemic circulation unchanged, while the therapeutic index indicates the safety margin of a drug by comparing the effective dose to the toxic dose. Understanding the half-life of a drug is essential for determining how frequently doses should be administered to maintain effective therapeutic levels while minimizing toxicity.