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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 Pharmacodynamics: 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 Table 2: Drug Therapy in the Elderly: 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, most nonselective antihistamines, some antipsychotic drugs, antiparkinsonian drugs with atropine-like activity, many OTC hypnotics and cold preparations) are anticholinergic. The elderly, most notably those with dementia, 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.
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Table 2
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PrintOpen table in new window  |
 | | |
| Effect of Aging on Drug Response |
|
Class
|
Drug
|
Action
|
Effect of Aging
|
|
Analgesics
|
Aspirin
|
Acute gastroduodenal mucosal damage
|
↔
|
|
|
Morphine
|
Acute analgesic effect
|
↑
|
|
|
Pentazocine
|
Analgesic effect
|
↑
|
|
Anticoagulants
|
Heparin
|
PTT
|
↔
|
|
|
Warfarin
|
PT
|
↑
|
|
Bronchodilators
|
Albuterol
|
Bronchodilation
|
↓
|
|
|
Ipratropium
|
Bronchodilation
|
↔
|
|
Cardiovascular drugs
|
Adenosine
|
Minute ventilation and heart rate response
|
↔
|
|
|
|
Venodilation
|
↔
|
|
|
Angiotensin II
receptor blockers
|
Decreased BP
|
↑
|
|
|
Diltiazem
|
Acute antihypertensive effect
|
↑
|
|
|
Dopamine
|
Increased creatinine clearance
|
↓
|
|
|
Enalapril
|
Acute antihypertensive effect
|
↑
|
|
|
Felodipine
|
Antihypertensive effect
|
↑
|
|
|
Histamine
|
Venodilation
|
↔
|
|
|
Isoproterenol
|
Increased heart rate
|
↓
|
|
|
|
Increased ejection fraction
|
↓
|
|
|
|
Venodilation
|
↓
|
|
|
Nitroglycerin
|
Venodilation
|
↔
|
|
|
Norepinephrine
|
Acute vasoconstriction
|
↔
|
|
|
Phenylephrine
|
Acute venoconstriction
|
↔
|
|
|
|
Acute hypertensive effect
|
↔
|
|
|
Prazosin
|
Acute antihypertensive effect
|
↔
|
|
|
Propranolol
|
Decreased heart rate
|
↔
|
|
|
Timolol
|
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 function
|
↑
|
|
|
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 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.
|
|
Last full review/revision September 2009 by J. Mark Ruscin, PharmD
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