Core33: Special groups - drug interactions: ageing

👴 High-yield / 要点：Elderly patients have altered PK + PD, reduced homeostatic reserve, multimorbidity, and polypharmacy → higher ADR/drug interaction risk.

Why elderly patients differ / 高齢者で注意する理由

• PK changes:
  • ↓ GI motility → absorption may change.
  • ↓ total body water and ↓ serum albumin → distribution changes.
  • ↓ hepatic metabolism.
  • ↓ GFR and renal elimination.
• Homeostatic changes:
  • Orthostatic hypotension tendency.
  • Weakened thermoregulation.
  • Cognitive decline → adverse effects can occur at lower doses.
• PD changes:
  • β-receptors respond less to bronchodilators.
  • Benzodiazepine receptors are more sensitive.
• Multimorbidity + polypharmacy → drug interactions increase.

Drugs requiring caution / 注意すべき薬

Drug/group	Main risk
Antihypertensives: ACE-I, ARB, β-blockers, CCB, diuretics	Postural hypotension
Sedatives: benzodiazepines, opioids	Hypothermia, cognitive worsening, falls, paradoxical agitation
Anticholinergics	Cognitive decline
Antipsychotics	Increased stroke risk in dementia
NSAIDs, aminoglycosides	Kidney damage
Digoxin	Adverse effects at lower doses due to increased sensitivity
Tricyclic antidepressants, e.g. amitriptyline	Cognitive decline, orthostatic hypotension, cardiotoxicity

Remember / 覚え方

• Elderly = less reserve + slower clearance
• Start low, go slow
• Sedatives/anticholinergics/NSAIDs/digoxin are high-yield caution drugs