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Pharmacodynamics in the Elderly

by J. Mark Ruscin, PharmD, Sunny A. Linnebur, PharmD, FCCP, BCPS, CGP

Pharmacodynamics is defined as what the drug does to the body or the response of the body to the drug; it is affected by receptor binding, postreceptor effects, and chemical interactions (see Drug–Receptor Interactions). In the elderly, the effects of similar drug concentrations at the site of action (sensitivity) may be greater or smaller than those in younger people (see Effect of Aging on Drug Response). Differences may be due to changes in drug-receptor interaction, in postreceptor events, or in adaptive homeostatic responses and, among frail patients, are often due to pathologic changes in organs.

Elderly patients are particularly sensitive to anticholinergic drug effects. Many drugs (eg, tricyclic antidepressants, sedating antihistamines, urinary antimuscarinic agents, some antipsychotic drugs, antiparkinsonian drugs with atropine-like activity, many OTC hypnotics and cold preparations) have anticholinergic effects. The elderly, most notably those with cognitive impairment, are particularly prone to CNS adverse effects of such drugs and may become more confused and drowsy. Anticholinergic drugs also commonly cause constipation, urinary retention (especially in elderly men with benign prostatic hyperplasia), blurred vision, orthostatic hypotension, and dry mouth. Even in low doses, these drugs can increase risk of heatstroke by inhibiting diaphoresis. In general, older adults should avoid drugs with anticholinergic effects when possible.

Effect of Aging on Drug Response

Class

Drug

Action

Effect of Aging

Analgesics

Morphine

Acute analgesic effect

Pentazocine

Analgesic effect

Anticoagulants

Heparin

PTT

Warfarin

PT/INR

Bronchodilators

Albuterol

Bronchodilation

Ipratropium

Bronchodilation

Cardiovascular drugs

Angiotensin II

receptor blockers

Decreased BP

Diltiazem

Acute antihypertensive effect

Dopamine

Increased creatinine clearance

Enalapril

Acute antihypertensive effect

Felodipine

Antihypertensive effect

Isoproterenol

Increased heart rate

Increased ejection fraction

Venodilation

Nitroglycerin

Venodilation

Norepinephrine

Acute vasoconstriction

Phenylephrine

Acute venoconstriction

Acute hypertensive effect

Prazosin

Acute antihypertensive effect

Propranolol (and other β-blockers)

Decreased heart rate

Verapamil

Acute antihypertensive effect, cardiac conduction effects

Diuretics

Bumetanide

Increased urine flow and Na excretion

Furosemide

Latency and size of peak diuretic response

Oral hypoglycemics

Glyburide

Chronic hypoglycemic effect

Tolbutamide

Acute hypoglycemic effect

Psychoactive drugs

Diazepam

Sedation

Diphenhydramine

Psychomotor dysfunction

Haloperidol

Acute sedation

Midazolam

EEG activity

Sedation

Temazepam

Postural sway

Psychomotor effect

Sedation

Thiopental

Anesthesia

Triazolam

Sedation

Others

Atropine

Impaired gastric emptying

Levodopa

Adverse effects

Metoclopramide

Sedation

=unchanged; = increased; = decreased.

Adapted and updated from Cusack BJ, Vestal RE: Clinical pharmacology: Special considerations in the elderly. In Practice of Geriatric Medicine , edited by E Calkins, PJ Davis, and AB Ford. Philadelphia, WB Saunders Company, 1986, pp. 115–136; used with permission.

Resources In This Article

Drugs Mentioned In This Article

  • Drug Name
    Select Trade
  • LEVOPHED
  • REGLAN
  • LASIX
  • No US brand name
  • ATROPEN
  • PLENDIL
  • HALCION
  • ATROVENT
  • DIABETA, GLYNASE
  • CARDIZEM, CARTIA XT, DILACOR XR
  • HALDOL
  • CALAN
  • MINIPRESS
  • VALIUM
  • PANHEPRIN
  • INDERAL
  • COUMADIN
  • TALWIN
  • No US trade name
  • DURAMORPH PF, MS CONTIN
  • PROVENTIL-HFA, VENTOLIN-HFA
  • VASOTEC
  • ISUPREL
  • NITRO-DUR
  • RESTORIL

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