Geriatric Pharmacology

Introduction — why the elderly are a special population

• Definition — geriatric pharmacology is the study of how the physiological changes of ageing alter drug handling (pharmacokinetics) and drug response (pharmacodynamics), and the consequent need to individualise drug choice, dose and regimen in older adults (conventionally ≥65 years, though functional decline is continuous from middle age).
• Age is a drug-modifying patient factor — age sits alongside body size, sex, genetics, route, disease and drug interactions as a factor that modifies drug action; its effects are usually quantitative (plasma level/effect shifts, correctable by dose adjustment) rather than qualitative.
• Why older adults are vulnerable — declining renal & hepatic clearance, altered body composition and lowered albumin combine with multimorbidity, polypharmacy and altered tissue sensitivity to widen the gap between effective and toxic drug exposure — a narrowed therapeutic margin.
• Excluded from pre-marketing trials — the elderly (with children, pregnant/lactating women and the organ-impaired) are routinely excluded from pre-marketing trials, so much geriatric dosing rests on extrapolation and Phase 4 / post-marketing surveillance rather than dedicated RCT data — a structural reason for cautious, individualised prescribing.