What are the different mechanisms of ADRs?

• A. On target adverse effects
• B. Off target adverse effects
• C. On target adverse effects; Off target adverse effects; production of toxic metabolite; production of harmful immune responses; idiosyncratic responses
• D. Idiosyncratic immune responses

Answer: (C)

Adverse drug reactions can arise through several distinct pathways, and a complete view includes multiple mechanisms rather than a single one. On-target adverse effects occur when the drug’s action at its intended target produces harmful effects as a side effect of the same mechanism that provides benefit. Off-target adverse effects happen when the drug affects other targets besides the intended one, leading to adverse outcomes in tissues where those unintended targets are present. Some ADRs result from metabolism to a toxic metabolite or reactive intermediate that damages cells or organs. Immune-mediated responses can be harmful when the drug or its metabolites trigger the immune system, causing hypersensitivity or inflammatory reactions. Finally, idiosyncratic responses are rare, unpredictable reactions driven by unique genetic, metabolic, or immune factors in an individual.

This combination best captures the full range of mechanisms and explains why ADRs occur in diverse ways. The other options describe only a single mechanism or a narrow subset, which doesn’t reflect the breadth of how ADRs can arise.