Which ADME stage primarily involves drug entry into systemic circulation after administration?

Prepare for the Drug Discovery and Healthcare Systems Test. Access flashcards and multiple-choice questions with hints and explanations. Ace your exam with our comprehensive resources!

The main idea tested is how a drug first enters the bloodstream after it’s given. Absorption is the step that governs entry into systemic circulation. It covers the process of moving the drug from its site of administration across biological barriers (like the intestinal lining for oral doses or the injection site walls) into the blood. The rate and extent of this entry depend on the route, formulation, and physiological factors such as gastric emptying and blood flow. Once the drug is in the bloodstream, distribution takes it to tissues, metabolism chemically alters it (often in the liver), and excretion removes it from the body. Note that intravenous administration bypasses the absorption step, since the drug is already in systemic circulation, but for other routes, absorption is the key gateway into the bloodstream.