Geriatric Pharmacology

Geriatric pharmacology studies how aging changes the way older adults handle and respond to medicines. With advancing age, declining renal clearance, reduced lean body mass, altered receptor sensitivity, and diminished homeostatic reserve combine to make many drugs act for longer and more intensely at a given dose. These changes, compounded by multimorbidity and polypharmacy, make older adults especially vulnerable to adverse drug effects.

Definition

The branch of clinical pharmacology concerned with age-related changes in drug pharmacokinetics and pharmacodynamics in older adults, and with the prescribing problems — polypharmacy, drug interactions, and inappropriate prescribing — that arise in this population.

Scope

The entry covers the pharmacokinetic and pharmacodynamic changes of aging, the heightened risk of adverse drug events and drug interactions in older adults, and the concept of potentially inappropriate prescribing addressed by explicit screening criteria. It is a reference overview and does not provide doses or individualized prescribing recommendations.

Core questions

• How does aging alter renal and hepatic clearance, body composition, and receptor sensitivity?
• Why are older adults more susceptible to adverse drug events and drug-drug interactions?
• What is 'potentially inappropriate prescribing', and how do explicit criteria identify it?
• How does polypharmacy amplify pharmacological risk in this population?

Key concepts

• Age-related decline in renal clearance
• Reduced lean body mass and altered distribution volume
• Altered pharmacodynamic sensitivity
• Reduced homeostatic reserve
• Polypharmacy and prescribing cascades
• Potentially inappropriate medications
• Anticholinergic burden
• Explicit prescribing criteria (STOPP/START, Beers)

Mechanisms

Aging shifts both how drugs are handled and how the body responds to them. Pharmacokinetically, glomerular filtration declines with age, prolonging the elimination of renally cleared drugs; lean body mass and total body water fall while fat mass tends to rise, changing the distribution volume of water- and fat-soluble drugs; and hepatic blood flow and first-pass metabolism may decrease. Pharmacodynamically, sensitivity to certain drug classes changes and homeostatic mechanisms — such as baroreceptor and thermoregulatory responses — become less able to buffer drug effects. Against this background, Ruxton and colleagues show in a systematic review and meta-analysis that medicines with anticholinergic effects are associated with cognitive impairment, falls, and mortality in older adults, illustrating how cumulative pharmacological burden translates into harm. Explicit criteria such as the STOPP/START tool described by O'Mahony and colleagues operationalize this knowledge by flagging potentially inappropriate medications and prescribing omissions. Rowland and Tozer provide the pharmacokinetic framework linking declining clearance to increased exposure.

Clinical relevance

Geriatric pharmacology underpins the cautious appraisal of medication use in older adults and the rationale behind prescribing-review tools. The topic describes why exposure and sensitivity differ with age and why polypharmacy raises risk; it supports critical reading of the evidence and does not provide doses or substitute for clinical judgement and current geriatric guidance.

Epidemiology

Older adults consume a disproportionate share of prescribed medicines and experience polypharmacy at high rates, which is associated with increased risk of adverse drug events, falls, and hospital admission. Potentially inappropriate prescribing is common in this group and is a target of quality-improvement efforts.

History

Awareness that older adults respond differently to medicines grew alongside the demographic aging of populations in the later twentieth century. Explicit screening tools emerged to make the resulting prescribing problems tractable — the Beers Criteria in the United States and, later, the European STOPP/START criteria — formalizing expert consensus on medications best avoided or considered in older people.

Debates

How useful are explicit prescribing criteria in routine care?

Tools such as STOPP/START and the Beers Criteria standardize the identification of potentially inappropriate prescribing, but they are consensus-based, vary between health systems, and cannot replace individualized clinical judgement, so their optimal role in practice is debated.

Key figures

• Denis O'Mahony
• Paul Gallagher
• Arduino Mangoni

Seminal works

• omahony-2014
• ruxton-2015

Frequently asked questions

Why are older adults more sensitive to many medicines?

Aging reduces renal and sometimes hepatic clearance, changes body composition and distribution volume, alters receptor sensitivity, and diminishes homeostatic reserve, so a standard dose can produce higher exposure and a stronger effect than in younger adults.

What does 'potentially inappropriate prescribing' mean?

It refers to medicines whose risks in older adults are judged to outweigh their benefits, or to omissions of beneficial therapy; explicit criteria such as STOPP/START and the Beers Criteria are used to identify such situations for review.