What best defines metabolism in pharmacology?

• A. Chemical modification of the drug through specialized enzymatic systems
• B. The body's ability to eliminate a drug from the blood in a specific period using various organs
• C. Absorption of the drug into the bloodstream
• D. Distribution of the drug to tissues

Answer: (A)

Metabolism in pharmacology refers to biotransformation: the chemical modification of drugs by enzymes, most often in the liver, to produce more water-soluble compounds that can be eliminated from the body. This usually involves two phases—Phase I reactions such as oxidation, reduction, or hydrolysis, which introduce or uncover a functional group, and Phase II reactions that conjugate these products to make them even more water-soluble. The products of metabolism can be less active, more active, or even become prodrugs that are activated by metabolic changes, which is why metabolism can alter a drug’s effect. This process is distinct from absorption (entry into the bloodstream) and distribution (movement to tissues) or elimination (removal from the body); metabolism specifically refers to the enzymatic chemical modification of the drug. For example, a drug might be inactive as given but become active after metabolic conversion, illustrating the transformative role of metabolism.