FPGEE for National Association of Boards of Pharmacy (NABP) Practice Exam

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What does ED50 signify in drug dosing?

  1. The amount of drug that produces a therapeutic response in half of the test group

  2. The concentration of drug that leads to an adverse effect

  3. The dose that results in a lethal effect

  4. The dose causing 50% of maximal effect

The correct answer is: The amount of drug that produces a therapeutic response in half of the test group

ED50, or the median effective dose, signifies the amount of drug required to produce a therapeutic response in half of a test population. This statistical measure is crucial in pharmacology as it helps to determine the efficacy of a drug and guides dosing recommendations. By establishing the ED50, researchers can compare the effectiveness of different drugs and assess how much of a drug is necessary to achieve a desired therapeutic effect in a significant portion of the population. While the other options present relevant concepts within pharmacology, they do not accurately capture the specific meaning of ED50. For instance, the concentration related to adverse effects pertains to toxicology and lends itself more to terms like TD50 (median toxic dose) rather than ED50. Similarly, a lethal effect would relate to the LD50 (median lethal dose), which is distinct from the therapeutic focus that ED50 represents. The option referring to the dose causing 50% of maximal effect misrepresents the concept as it implies a context that differs from its definition. Hence, recognizing ED50's role in determining effective dosages in therapeutic settings is fundamental to proper pharmacotherapy.