Challenges in Medication Adherence in Advanced Age

In advanced age, the effects of medications at the site of action (sensitivity) can be greater or smaller than those in younger age. Differences may be attributed to changes in drug-receptor interactions, post-receptor processes, or adaptive homeostatic reactions, often stemming from pathological changes in organs. However, clinical differentiation between pharmacodynamic and pharmacokinetic effects can sometimes be challenging.

Unlike pharmacokinetics (the metabolism of drugs by the body), pharmacodynamics is defined as the molecular, biochemical, and physiological actions of a given drug or the effects the drug has on the body or the body’s response to the drug. Pharmacodynamics is influenced by receptor binding, post-receptor processes, and chemical interactions within the body.

Problems associated with medication adherence are often encountered in older individuals and include drug ineffectiveness, adverse drug effects, overdosing, underdosing, inappropriate treatment, inadequate monitoring, non-compliance, and drug interactions.

Side effects of medications are reactions that are unwanted, cause discomfort, or are hazardous to health. Common examples include oversedation, confusion, hallucinations, falls, and bleeding. In individuals aged over 65, adverse drug effects manifest more frequently. Cases of hospitalization due to unwanted drug reactions are four times higher in older patients (around 17%) compared to younger ones (4%).

Which medications most commonly cause adverse reactions in advanced age?

In advanced age, sensitivity to anticholinergic drug effects increases. Numerous medications have anticholinergic effects, including tricyclic antidepressants, sedative antihistamines, antimuscarinic agents, certain antipsychotic drugs, antiparkinsonian drugs with atropine-like activity, many over-the-counter hypnotics, and motion sickness drugs.

Older patients, especially those with cognitive impairment, are particularly predisposed to adverse drug effects on the central nervous system (CNS) from medications that can lead to confusion and drowsiness. Anticholinergic drugs often cause dry mouth, blurred vision, orthostatic hypotension, and urine retention (especially in older men with benign prostatic hyperplasia). Even in low doses, these drugs can increase the risk of heat stroke by inhibiting sweating. Overall, older individuals should avoid medications with anticholinergic effects whenever possible.

66% of hospitalizations due to adverse drug reactions in older patients are attributed to 4 medications or drug classes – warfarin, insulin, oral antiplatelet drugs, and oral hypoglycemic drugs.