pharmacodynamics in elderly

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.

Table 2

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

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