What are the three types of drug-drug interactions?

• A. Enzyme inhibition 2. Enzyme induction 3. Potentiation of pharmacologic effect
• B. Pharmacodynamic interactions 2. Pharmacokinetic interactions 3. Genetic interactions
• C. Absorption interference 2. Metabolic inhibition 3. Additive toxicity
• D. Allosteric effects 2. Competitive antagonism 3. Synergistic effects

Answer: (A)

The main concept is that drug–drug interactions are categorized by how they change exposure or effect: two mechanisms that alter drug levels (pharmacokinetic) and one that changes the effect itself (pharmacodynamic).

Enzyme inhibition is a pharmacokinetic interaction where blocking metabolism raises the other drug’s levels, potentially increasing toxicity. Enzyme induction is the opposite: it speeds up metabolism, lowering drug levels and possibly reducing efficacy. Potentiation of pharmacologic effect is a pharmacodynamic interaction where two drugs produce a greater effect together than expected from their individual effects, without necessarily changing concentrations.

These three items together illustrate the common way this question frames the types of interactions: metabolic (inhibition and induction) plus interaction at the level of effect (potentiation). Other options mix concepts that aren’t typically the standard three-type framework—for example, genetic interactions aren’t universally listed as a primary interaction type, and other choices describe specific mechanisms or outcomes rather than a broad three-category classification.