Age-Related Adverse Drug Effects

Age-related adverse drug effects describe how the very young and the very old differ from average adults in the way they handle and respond to medicines, and why these differences raise their risk of harm. Immaturity of organ systems in neonates and children, and the physiological decline, multimorbidity, and polypharmacy of later life, all shift drug exposure and sensitivity, making age one of the most consistently identified risk factors in pharmacovigilance.

Definition

Age-related adverse drug effects are adverse drug reactions whose probability or severity is modified by the patient's age, through developmental or ageing-related changes in pharmacokinetics and pharmacodynamics and through the comorbidity and polypharmacy that accompany the extremes of life.

Scope

The topic covers age as a determinant of drug safety across the lifespan, with emphasis on the two extremes: paediatric patients, in whom developing physiology changes drug handling, and older adults, in whom declining clearance, altered pharmacodynamic sensitivity, polypharmacy, and geriatric syndromes converge. It is a reference account of why age modifies risk and how this is studied; it does not give age-specific dosing or treatment instructions.

Core questions

• How do drug handling and drug response differ in children and in older adults?
• Why is age repeatedly identified as a risk factor for adverse drug reactions?
• How do polypharmacy, multimorbidity, and geriatric syndromes amplify drug-related harm in later life?
• How are potentially inappropriate medications in older adults identified and described?

Key concepts

• Developmental pharmacology in neonates and children
• Age-related decline in renal and hepatic clearance
• Altered pharmacodynamic sensitivity with ageing
• Polypharmacy and drug-drug interactions
• Multimorbidity
• Geriatric syndromes (e.g. falls, delirium)
• Potentially inappropriate medications
• Anticholinergic and sedative burden

Mechanisms

Age changes both how much drug the body is exposed to and how strongly it responds. In children, immature metabolizing enzymes, changing body composition, and developing renal function make drug handling a moving target across infancy and childhood. In older adults, reduced renal clearance, modest declines in hepatic metabolism and blood flow, lower lean body mass and total body water, and altered receptor responsiveness shift both pharmacokinetics and pharmacodynamics, often increasing exposure and sensitivity to a given dose (Mangoni & Jackson, 2003). These physiological changes interact with the high prevalence of multiple chronic conditions and polypharmacy in later life, multiplying the chance of drug-drug interactions and of drugs precipitating geriatric syndromes such as falls and delirium (Inouye et al., 2007). Together these mechanisms make age a powerful modifier of adverse-reaction risk.

Clinical relevance

Age-related effects account for a large and partly preventable share of drug-related harm, and adverse reactions are a documented cause of hospital admission that falls disproportionately on older patients (Pirmohamed et al., 2004). Consensus tools such as the Beers Criteria catalogue medications considered potentially inappropriate in older adults as a reference resource (American Geriatrics Society Beers Criteria Update Expert Panel, 2023). This entry explains why age modifies risk; it is descriptive and does not prescribe doses or treatments for any age group.

Epidemiology

Prospective hospital studies repeatedly find older age, multimorbidity, and polypharmacy among the strongest correlates of adverse drug reactions leading to admission (Pirmohamed et al., 2004). At the other extreme, children — and especially neonates — are recognized as a population in whom limited age-specific evidence and developmental physiology heighten uncertainty about drug safety.

History

Attention to age in drug safety grew from the recognition that infants are not small adults and that older patients accumulate risk through declining organ function and accumulating medications. The articulation of geriatric syndromes as a unifying concept and the development of explicit lists of potentially inappropriate medications marked the consolidation of age as a formal pharmacovigilance concern (Inouye et al., 2007; American Geriatrics Society Beers Criteria Update Expert Panel, 2023).

Debates

How useful are explicit 'potentially inappropriate medication' lists?

Criteria such as the Beers list provide a transparent reference for medications carrying heightened risk in older adults, but they are explicitly advisory and their direct effect on outcomes and their applicability across settings remain discussed.

Seminal works

• mangoni-2003
• inouye-2007
• beers-2023

Frequently asked questions

Why are older adults more likely to have adverse drug reactions?

Ageing reduces drug clearance and changes drug sensitivity, and older patients more often take several medicines for several conditions at once, so interactions and accumulated risk are more common.

Why is drug safety treated differently in children?

Children's organs and body composition are still developing, so they handle drugs differently from adults, and age-specific safety evidence is often more limited.