Which of the following lists the three mechanisms of toxicity?

• A. Dose-dependent toxicity; drug-drug interactions; idiosyncratic reactions
• B. Dose-dependent only
• C. Drug-drug interactions only
• D. Idiosyncratic reactions only

Answer: (A)

Toxicity can arise in three main ways: dose-related toxicity, which increases with the amount of drug taken; drug-drug interactions, where another medication changes the way a drug is metabolized or its effect, increasing harm; and idiosyncratic reactions, which are unpredictable and not tied to the dose, often related to individual genetics or immune responses. This question lists all three mechanisms, making it the most complete and accurate choice. For example, high doses of a drug can directly cause organ damage (dose-dependent toxicity); combining drugs can elevate levels or effects and trigger toxicity (drug-drug interactions); and a rare subset of people might develop severe reactions at any dose due to genetic or immune factors (idiosyncratic reactions). The other options mention only one mechanism, missing the others that can also lead to toxicity.