Which of the following is explicitly a Phase IV subcategory?

• A. Drug-Drug Interactions
• B. Pre-approval risk assessment
• C. Dose justification
• D. Animal models

Answer: (A)

Phase IV focuses on post-marketing safety, real-world use, and how a drug interacts with other medications or factors after approval. Drug-drug interactions fit this post-marketing focus, since monitoring and understanding how a drug combines with concomitant medicines, foods, or disease states is a key part of pharmacovigilance and ongoing labeling updates. The other options are tied to earlier stages: pre-approval risk assessment happens before a drug is approved, dose justification is determined during early-phase trials, and animal models are preclinical studies done before human testing. So the explicit Phase IV subcategory is the drug-drug interactions.