Drug interaction

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In pharmaceutical sciences, drug interactions occur when a drug's mechanism of action is affected by the concomitant administration of substances such as foods, beverages, or other drugs. A popular example of drug-food interaction is the effect of grapefruit in the metabolism of drugs.

Interactions may occur by simultaneous targeting of receptors, directly or indirectly. For example, both Zolpidem and alcohol affect GABA_A receptors, and their simultaneous consumption results in the overstimulation of the receptor, which can lead to loss of consciousness. When two drugs affect each other, it receives the name of a drug-drug interaction. The risk of a drug-drug interaction (DDI) increases with the number of drugs used.^[1]

A large share of elderly people regularly use five or more medications or supplements, with a significant sharte risk of side-effects from drug-drug interactions.^[2]

Drug interactions can be of three kinds:

• additive (the result is what you expect when you add together the effect of each drug taken independently),
• synergistic (combining the drugs leads to a larger effect than expected), or
• antagonistic (combining the drugs leads to a smaller effect than expected).^[3]

It may be difficult to distinguish between synergistic or additive interactions, as individual effects of drugs may vary.

Direct interactions between drugs are also possible and may occur when two drugs are mixed before intravenous injection. For example, mixing thiopentone and suxamethonium can lead to the precipitation of thiopentone.^[4]