Drug interaction

A change in a drug’s effects or concentration caused by another drug, food, supplement, or other substance. Interactions can increase harm, reduce benefit, or alter how quickly a drug is processed.

Cytochrome P450: A family of enzymes that metabolizes many drugs and other chemicals, especially in the liver. Inhibition or induction of these enzymes can raise or lower concentrations of affected drugs.
Drug interaction checker: A reference tool that screens combinations of medicines and other substances for potential interactions. These tools help flag combinations that may need monitoring, dose changes, or avoidance.
Pharmacokinetic interaction: A drug interaction that changes another drug’s absorption, distribution, metabolism, or excretion. This is the interaction type that changes a drug’s concentration in the body.
Bioavailability: The fraction of an administered dose that reaches systemic circulation in an active form. Interactions that alter absorption can change a drug’s bioavailability.
Grapefruit–drug interactions: Interactions in which grapefruit or its juice alters the exposure of certain medicines. Grapefruit can inhibit intestinal enzymes and raise concentrations of susceptible drugs.
Drug metabolism: The chemical modification of drugs by the body, often making them easier to eliminate. Many interactions occur when one substance changes how another is metabolized.
Medication reconciliation: The process of compiling and verifying a patient’s complete medication list across care transitions. An accurate list can reveal interactions involving prescriptions, over-the-counter drugs, and supplements.
Pharmacodynamic interaction: A drug interaction in which combined effects change without necessarily altering drug concentrations. This distinguishes effects at receptors or physiological systems from changes in drug exposure.
Half-life: The time required for a drug’s concentration in the body to fall by half. A long half-life can make interaction effects persist after a substance is stopped.
Warfarin–vitamin K interaction: The effect of dietary vitamin K on warfarin’s anticoagulant action. Changes in vitamin K intake can alter warfarin response and complicate stable anticoagulation.

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