In pharmacokinetics, which phase is primarily involved?

• A. Distribution phase
• B. Excretion phase
• C. Absorption phase
• D. Metabolism phase

Answer: (C)

The main concept here is how a drug enters systemic circulation after administration. Absorption is the process by which drug molecules move from the site of administration into the bloodstream. It sets how much of the dose actually reaches the blood (bioavailability) and how quickly the drug begins to work. Factors like the route (oral, sublingual, inhaled, topical), formulation and solubility, dissolution rate, and GI conditions all influence absorption. After absorption, the drug then distributes to tissues, is metabolized, and is excreted, which are the subsequent pharmacokinetic phases. In the case of intravenous administration, absorption isn’t involved, but for most routes, absorption is the phase that brings the drug into circulation.