Which item is NOT listed as a mechanism of toxicity?

• A. Dose-dependent
• B. Pharmacokinetic alteration (exposure)
• C. Drug-drug interactions
• D. Idiosyncratic reactions

Answer: (B)

The idea being tested is how toxicity is produced. A dose-dependent effect is a mechanism because the adverse outcome arises directly as exposure increases—higher dose means greater risk and severity, reflecting a causal link between amount of drug and harm. Drug-drug interactions are a mechanism too because they alter how a drug is handled or its pharmacologic effect, leading to greater or prolonged exposure or additive toxicity. Idiosyncratic reactions are also a mechanism, representing unpredictable toxic responses that aren’t explained by dose or exposure and often involve immune or metabolic processes.

Pharmacokinetic alteration (exposure) describes changes in how much drug reaches the tissues due to absorption, distribution, metabolism, or excretion. This is a factor that modifies risk by changing exposure, but it isn’t, by itself, a mechanism of toxicity in this framework. It explains why toxicity might occur, whereas the others describe the biological processes that cause harm. So it’s the item that isn’t listed as a mechanism of toxicity in this context.