Drug interaction
[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.
[6] For example, low blood glucose leads to a release of catecholamines, triggering symptoms that hint the organism to take action, like consuming sugary foods.
Pharmacokinetics is the field of research studying the chemical and biochemical factors that directly affect dosage and the half-life of drugs in an organism, including absorption, transport, distribution, metabolism and excretion.
For example, prokinetic agents increase the intestinal motility, which may cause drugs to go through the digestive system too fast, reducing absorption.
Drugs can be present in ionized or non-ionized forms depending on pKa, and neutral compounds are usually better absorbed by membranes.
[7] Medication like antacids can increase pH and inhibit the absorption of other drugs such as zalcitabine, tipranavir and amprenavir.
[citation needed] The formation of non-absorbable complexes may occur also via chelation, when cations can make certain drugs harder to absorb, for example between tetracycline or the fluoroquinolones and dairy products, due to the presence of calcium ions.
This appears to be one of the mechanisms by which grapefruit juice increases the bioavailability of various drugs beyond its inhibitory activity on first pass metabolism.
This alteration results in drug A remaining in the bloodstream for an extended duration, and eventually increase in concentration.
The following table shows the most common: Drugs tightly bound to proteins (i.e. not in the free fraction) are not available for renal excretion.
[21] The most commonly implicated conventional drugs in herb-drug interactions are warfarin, insulin, aspirin, digoxin, and ticlopidine, due to their narrow therapeutic indices.
[21][22] The most commonly implicated herbs involved in such interactions are those containing St. John’s Wort, magnesium, calcium, iron, or ginkgo.
In addition, in old age, there is a sensory decrease that increases the chances of errors being made in the administration of drugs.
[citation needed] Patients with hepatic or renal diseases already may have difficulties metabolizing and excreting drugs, which may exacerbate the effect of interactions.
[29] 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.
