Drug interaction
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 on the metabolism of drugs.
Interactions may occur by simultaneous targeting of receptors, directly or indirectly. For example, both Zolpidem and alcohol affect GABAA 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 is a drug–drug interaction (DDI). The risk of a 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 risk of side-effects from drug–drug interactions.[2]
Drug interactions can be of three kinds:
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]
Underlying factors[edit]
The factors or conditions that predispose the appearance of interactions include factors such as old age.[26] This is where human physiology changing with age may affect the interaction of drugs. For example, liver metabolism, kidney function, nerve transmission, or the functioning of bone marrow all decrease with age. In addition, in old age, there is a sensory decrease that increases the chances of errors being made in the administration of drugs.[27] The elderly are also more vulnerable to polypharmacy, and the more drugs a patient takes, the higher is the chance of an interaction.[28]
Genetic factors may also affect the enzymes and receptors, thus altering the possibilities of interactions.
Parients with hepatic or renal diseases already may have difficulties metabolizing and excreding drugs, what may exacerbate the effect of interactions.[28]
Some drugs present an intrinsic increased risk for a harmful interaction, including drugs with a narrow therapeutic index, where the difference between the effective dose and the toxic dose is small.[n. 1] The drug digoxin is an example of this type of drug.[29]
Risks are also increased when the drug presents a steep dose-response curve, and small changes in the dosage produce large changes in the drug's concentration in the blood plasma.[29]
Epidemiology[edit]
As of 2008, among adults in the United States of America older than 56, 4% were taking medication and/ or supplements that put them at risk of a major drug interaction.[30] Potential drug-drug interactions have increased over time[31] and are more common in the less-educated elderly even after controlling for age, sex, place of residence, and comorbidity.[32]