Which process describes the movement of a drug from the site of administration into the systemic circulation?

• A. Liberation
• B. Absorption
• C. Biotransformation
• D. Excretion

Answer: (B)

Absorption is the movement of a drug from the site of administration into the systemic circulation. After the dosage form releases the drug (liberation), the active drug must dissolve and cross biological membranes to reach the bloodstream. The rate and extent of absorption depend on factors like the route taken (oral, sublingual, inhaled, topical), the drug’s solubility and ability to cross lipid membranes, particle size or ionization, and the local blood flow at the absorption site. This step sets how quickly and how much of the drug enters the bloodstream, which then leads to distribution, possible biotransformation (metabolism), and eventual excretion. Liberation is the release from the dosage form and is a prerequisite for absorption, while biotransformation and excretion occur after absorption.