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Geriatrics and pharmacology


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Geriatrics and pharmacology

  1. 1. Slide 1 © 2001 By Default! Pharmacologic Considerations Geriatrics
  2. 2. Slide 2 © 2001 By Default! Introduction  In the US, the elderly (>65y/o) constitute ~12% of the total population, but account for almost 30% of total drug expenditure  Age-related physiologic changes make the elderly susceptible to adverse effects  Understanding the influence these changes have on the pharmacokinetics and pharmacodynamics of the elderly is essential to prevent harm
  3. 3. Slide 3 © 2001 By Default! Physiologic Changes of Aging Affecting Absorption  Physiologic change – Decreased gastric acidity – Decreased gastrointestinal blood flow – Delayed grastric emptying – Slowed intestinal transit time  General clinical effect – None on passive diffusion or bioavailability for most drugs – Decreased active transport: Decreased bioavailability for some drugs – Decreased first-pass effect: Increased bioavailability for some drugs  Special considerations – Antacids decrease absorption of acidic drugs: digitalis, phenytoin, tetracycline – Anticholinergics: Slow GI motility and absorption rate
  4. 4. Slide 4 © 2001 By Default! Physiologic Changes of Aging Affecting Distribution  Decreased Total body water – Decreased Volume Distribution – Increased Plasma Conc. of water soluble drugs – Lower doses are required: Lithium, digoxin, ethanol, etc  Decreased Lean body mass and Increased body fat – Increased Volume Distribution, Longer (t½) of water soluble drugs – Accumulation into fat of lipid soluble drugs: Benzos, etc  Decreased Serum Albumin – Increased unbound fraction of highly protein bound drugs – Binds acidic drugs: warfarin, phenytoin, digitalis, etc  Decreased Alpha1 Acid glycoprotein – Increased unbound fraction of highly protein bound drugs – -Binds basic drugs: lidocaine and propranolol, etc
  5. 5. Slide 5 © 2001 By Default! Metabolism  Determined – Primarily by hepatic function and blood flow – Capacity of the liver to metabolize drugs does not appear to decline consistently with age for all drugs
  6. 6. Slide 6 © 2001 By Default! Elimination  Determined – Primarily by renal function – Declines with age and is worsened by co-morbidities – Decline is not reflected in an equivalent rise in serum creatinine since creatinine production is reduced due to lower muscle mass
  7. 7. Slide 7 © 2001 By Default! Physiologic Changes of Aging Affecting Elimination  Physiologic change – Decreased GFR – Decreased renal blood flow – Decreased renal mass  General clinical effect – Decreased clearance, Increased (t½) of renally eliminated drugs
  8. 8. Slide 8 © 2001 By Default! Pharmacodynamics  Pharmacodynamic changes in the elderly have been less extensively studied  Evidence of enhanced end-organ responsiveness or “sensitivity” to medications with aging  Enhanced “sensitivity” may be due – Changes in receptor affinity – Changes in receptor number – Post-receptor alteration – Age-related impairment of homeostatic mechanisms Example: decreased baroreceptor reflexes
  9. 9. Slide 9 © 2001 By Default! Major Drug Groups Requiring Monitoring  CNS drugs – Sedative-hypnotics: Benzodiazepines and barbiturates – Analgesics: Opioids – Antipsychotic, antidepressants: Haloperidol, lithium, TCAs  Cardiovascular drugs – Antihypertensives: Thiazides, beta-blockers  Antiarrhythmic drugs – Quinidine and procainamide: ↓ clearance and ↑ (t½)  Antimicrobial drugs – Beta-lactams and aminoglycosides: ↓ clearance  Anti-inflammatory drugs – NSAIDs: GI bleed and irritation
  10. 10. Slide 10 © 2001 By Default! Major Reasons for Adverse Drug Reactions in the Elderly  Positive relationship between number of drugs taken and incidence  Overall incidence is estimated to be at least twice that in the younger population  Prescribing errors – Polypharmacy – Drug interactions with other prescriptions – Unawareness of age related physiologic changes  Drug usage errors – “Hidden ingredients”: OTCs
  11. 11. Slide 11 © 2001 By Default! Compliance  There are several practical obstacles to compliance that the prescriber must recognize – Forgetfulness – Prior experience – Physical disabilities  Recommendations to improve compliance – Take careful drug history – Prescribe only for a specific and rational indication – Define goal of drug therapy – High index of suspicion regarding drug reactions and interactions – Simplify drug regimen