Pharmacodynamics in the Elderly: Drug Therapy in the Elderly: Merck Manual Professional

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Drug Therapy in the Elderly

Pharmacodynamics in the Elderly

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Pharmacodynamics in the Elderly

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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 atropineSome Trade Names
ATROPEN
ATROPINE-CARE
SAL-TROPINE
Click for Drug Monograph
-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

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Effect of Aging on Drug Response
Class	Drug	Action	Effect of Aging
Analgesics	AspirinSome Trade Names BUFFERIN ECOTRIN GENACOTE Click for Drug Monograph	Acute gastroduodenal mucosal damage	↔
	MorphineSome Trade Names DURAMORPH MS CONTIN MSIR ROXANOL Click for Drug Monograph	Acute analgesic effect	↑
	PentazocineSome Trade Names TALWIN Click for Drug Monograph	Analgesic effect	↑
Anticoagulants	HeparinSome Trade Names HEPFLUSH-10 Click for Drug Monograph	PTT	↔
	WarfarinSome Trade Names COUMADIN Click for Drug Monograph	PT	↑
Bronchodilators	AlbuterolSome Trade Names PROVENTIL VENTOLIN Click for Drug Monograph	Bronchodilation	↓
	IpratropiumSome Trade Names ATROVENT Click for Drug Monograph	Bronchodilation	↔
Cardiovascular drugs	AdenosineSome Trade Names ADENOCARD Click for Drug Monograph	Minute ventilation and heart rate response	↔
		Venodilation	↔
	Angiotensin II receptor blockers	Decreased BP	↑
	DiltiazemSome Trade Names CARDIZEM CARTIA DILACOR Click for Drug Monograph	Acute antihypertensive effect	↑
	DopamineSome Trade Names INTROPIN Click for Drug Monograph	Increased creatinine clearance	↓
	EnalaprilSome Trade Names VASOTEC Click for Drug Monograph	Acute antihypertensive effect	↑
	FelodipineSome Trade Names PLENDIL Click for Drug Monograph	Antihypertensive effect	↑
	Histamine	Venodilation	↔
	IsoproterenolSome Trade Names ISUPREL Click for Drug Monograph	Increased heart rate	↓
		Increased ejection fraction	↓
		Venodilation	↓
	NitroglycerinSome Trade Names NITRO-BID NITRO-DUR NITROL NITROQUICK Click for Drug Monograph	Venodilation	↔
	NorepinephrineSome Trade Names LEVOPHED Click for Drug Monograph	Acute vasoconstriction	↔
	PhenylephrineSome Trade Names NEO-SYNEPHRINE Click for Drug Monograph	Acute venoconstriction	↔
		Acute hypertensive effect	↔
	PrazosinSome Trade Names MINIPRESS Click for Drug Monograph	Acute antihypertensive effect	↔
	PropranololSome Trade Names INDERAL Click for Drug Monograph	Decreased heart rate	↔
	TimololSome Trade Names BLOCADREN TIMOPTIC Click for Drug Monograph	Decreased heart rate	↔
	VerapamilSome Trade Names CALAN ISOPTIN Click for Drug Monograph	Acute antihypertensive effect, cardiac conduction effects	↑
Diuretics	BumetanideSome Trade Names BUMEX Click for Drug Monograph	Increased urine flow and Na excretion	↓
	FurosemideSome Trade Names LASIX Click for Drug Monograph	Latency and size of peak diuretic response	↓
Oral hypoglycemics	GlyburideSome Trade Names DIABETA GLYNASE MICRONASE Click for Drug Monograph	Chronic hypoglycemic effect	↔
	TolbutamideSome Trade Names ORINASE Click for Drug Monograph	Acute hypoglycemic effect	↓
Psychoactive drugs	DiazepamSome Trade Names VALIUM Click for Drug Monograph	Sedation	↑
	DiphenhydramineSome Trade Names BENADRYL NYTOL Click for Drug Monograph	Psychomotor function	↑
	HaloperidolSome Trade Names HALDOL Click for Drug Monograph	Acute sedation	↑
	MidazolamSome Trade Names No US trade name Click for Drug Monograph	EEG activity	↑
		Sedation	↑
	TemazepamSome Trade Names RESTORIL Click for Drug Monograph	Postural sway	↑
		Psychomotor effect	↑
		Sedation	↑
	ThiopentalSome Trade Names PENTOTHAL Click for Drug Monograph	Anesthesia	↔
	TriazolamSome Trade Names HALCION Click for Drug Monograph	Sedation	↔
Others	AtropineSome Trade Names ATROPEN ATROPINE-CARE SAL-TROPINE Click for Drug Monograph	Impaired gastric emptying	↔
	Levodopa	Adverse effects	↑
	MetoclopramideSome Trade Names REGLAN Click for Drug Monograph	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.

Effect of Aging on Drug Response

Class

Drug

Action

Effect of Aging

Analgesics	AspirinSome Trade Names BUFFERIN ECOTRIN GENACOTE Click for Drug Monograph	Acute gastroduodenal mucosal damage	↔
	MorphineSome Trade Names DURAMORPH MS CONTIN MSIR ROXANOL Click for Drug Monograph	Acute analgesic effect	↑
	PentazocineSome Trade Names TALWIN Click for Drug Monograph	Analgesic effect	↑
Anticoagulants	HeparinSome Trade Names HEPFLUSH-10 Click for Drug Monograph	PTT	↔
	WarfarinSome Trade Names COUMADIN Click for Drug Monograph	PT	↑
Bronchodilators	AlbuterolSome Trade Names PROVENTIL VENTOLIN Click for Drug Monograph	Bronchodilation	↓
	IpratropiumSome Trade Names ATROVENT Click for Drug Monograph	Bronchodilation	↔
Cardiovascular drugs	AdenosineSome Trade Names ADENOCARD Click for Drug Monograph	Minute ventilation and heart rate response	↔
		Venodilation	↔
	Angiotensin II receptor blockers	Decreased BP	↑
	DiltiazemSome Trade Names CARDIZEM CARTIA DILACOR Click for Drug Monograph	Acute antihypertensive effect	↑
	DopamineSome Trade Names INTROPIN Click for Drug Monograph	Increased creatinine clearance	↓
	EnalaprilSome Trade Names VASOTEC Click for Drug Monograph	Acute antihypertensive effect	↑
	FelodipineSome Trade Names PLENDIL Click for Drug Monograph	Antihypertensive effect	↑
	Histamine	Venodilation	↔
	IsoproterenolSome Trade Names ISUPREL Click for Drug Monograph	Increased heart rate	↓
		Increased ejection fraction	↓
		Venodilation	↓
	NitroglycerinSome Trade Names NITRO-BID NITRO-DUR NITROL NITROQUICK Click for Drug Monograph	Venodilation	↔
	NorepinephrineSome Trade Names LEVOPHED Click for Drug Monograph	Acute vasoconstriction	↔
	PhenylephrineSome Trade Names NEO-SYNEPHRINE Click for Drug Monograph	Acute venoconstriction	↔
		Acute hypertensive effect	↔
	PrazosinSome Trade Names MINIPRESS Click for Drug Monograph	Acute antihypertensive effect	↔
	PropranololSome Trade Names INDERAL Click for Drug Monograph	Decreased heart rate	↔
	TimololSome Trade Names BLOCADREN TIMOPTIC Click for Drug Monograph	Decreased heart rate	↔
	VerapamilSome Trade Names CALAN ISOPTIN Click for Drug Monograph	Acute antihypertensive effect, cardiac conduction effects	↑
Diuretics	BumetanideSome Trade Names BUMEX Click for Drug Monograph	Increased urine flow and Na excretion	↓
	FurosemideSome Trade Names LASIX Click for Drug Monograph	Latency and size of peak diuretic response	↓
Oral hypoglycemics	GlyburideSome Trade Names DIABETA GLYNASE MICRONASE Click for Drug Monograph	Chronic hypoglycemic effect	↔
	TolbutamideSome Trade Names ORINASE Click for Drug Monograph	Acute hypoglycemic effect	↓
Psychoactive drugs	DiazepamSome Trade Names VALIUM Click for Drug Monograph	Sedation	↑
	DiphenhydramineSome Trade Names BENADRYL NYTOL Click for Drug Monograph	Psychomotor function	↑
	HaloperidolSome Trade Names HALDOL Click for Drug Monograph	Acute sedation	↑
	MidazolamSome Trade Names No US trade name Click for Drug Monograph	EEG activity	↑
		Sedation	↑
	TemazepamSome Trade Names RESTORIL Click for Drug Monograph	Postural sway	↑
		Psychomotor effect	↑
		Sedation	↑
	ThiopentalSome Trade Names PENTOTHAL Click for Drug Monograph	Anesthesia	↔
	TriazolamSome Trade Names HALCION Click for Drug Monograph	Sedation	↔
Others	AtropineSome Trade Names ATROPEN ATROPINE-CARE SAL-TROPINE Click for Drug Monograph	Impaired gastric emptying	↔
	Levodopa	Adverse effects	↑
	MetoclopramideSome Trade Names REGLAN Click for Drug Monograph	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

Content last modified February 2012

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