Which of the following is an example of a pharmacodynamic related ADR?

• A. A drug binding to its intended therapeutic target to produce a desired effect.
• B. Drugs that increase metabolism via enzyme induction.
• C. Co-administration of two or more drugs that share the same receptor/target or signaling pathway.
• D. Ginkgo biloba with NSAIDs.

Answer: (C)

Pharmacodynamic adverse drug reactions come from how drugs affect the body, especially when two or more drugs act on the same receptor or signaling pathway. When drugs share a target, their combined effect can be additive or even synergistic, pushing the response into toxicity or causing unexpected adverse effects.

Choosing two drugs that both hit the same receptor or pathway is a classic example of a PD interaction, because the ADR arises from the overlap in their actions at the target, not from changes in drug levels or metabolism. The other options describe actions that are not ADRs (a drug producing its intended effect) or involve changes in drug concentration through metabolism (a pharmacokinetic issue). The example of combining agents that act on the same target best illustrates a pharmacodynamic related ADR.