Which description best defines metabolism of a drug?

• A. Diffusion into tissues
• B. Conversion to inactive form (usually via liver)
• C. Elimination via urine
• D. Coated medication to survive stomach

Answer: (B)

Metabolism of a drug means its biotransformation in the body, mainly by liver enzymes, into more water-soluble compounds that are easier to eliminate. This process often inactivates the drug, producing inactive metabolites, though it can also generate active metabolites or prodrugs in some cases. This hepatic conversion is a key reason why oral drugs may have reduced bioavailability due to first-pass metabolism before reaching systemic circulation. The other processes mentioned describe distribution into tissues, excretion via the kidneys, or formulation strategies to protect the drug in the stomach, not metabolism itself. Therefore, converting to an inactive form via the liver best defines metabolism.