In contrast to pharmacokinetic effects, 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 older adults, the effects of similar drug concentrations at the site of action (sensitivity) may be greater or smaller than those in younger people (see table Effect of Aging on Drug Response). Differences may be due to changes in drug-receptor interaction, postreceptor events, or adaptive homeostatic responses and, among frail patients, are often due to pathologic changes in organs. However, clinical differentiation between pharmacodynamic and pharmacokinetic effects can sometimes be difficult.
Effect of Aging on Drug Response
Class | Drug | Action | Effect of Aging |
|---|---|---|---|
Analgesics | Acute analgesic effect | ↑ | |
Pentazocine | Analgesic effect | ↑ | |
Anticoagulants | PTT (partial thromboplastin time) | ↔ | |
PT/INR (prothrombin time/international normalized ratio) | ↑ | ||
Bronchodilators | Bronchodilation | ↓ | |
Bronchodilation | ↔ | ||
Cardiovascular drugs | receptor blockers | Decreased blood pressure | ↑ |
Acute antihypertensive effect | ↑ | ||
Acute antihypertensive effect | ↑ | ||
Antihypertensive effect | ↑ | ||
Increased heart rate | ↓ | ||
Increased ejection fraction | ↓ | ||
Venodilation | ↓ | ||
Venodilation | ↔ | ||
Acute vasoconstriction | ↔ | ||
Acute venoconstriction | ↔ | ||
Acute hypertensive effect | ↔ | ||
Acute antihypertensive effect | ↔ | ||
Decreased heart rate | ↓ | ||
Acute antihypertensive effect, cardiac conduction effects | ↑ | ||
Diuretics | Increased urine flow and sodium excretion | ↓ | |
Latency and size of peak diuretic response | ↓ | ||
Oral hypoglycemics | Chronic hypoglycemic effect | ↑ | |
Psychoactive drugs | Sedation | ↑ | |
Psychomotor dysfunction | ↑ | ||
Acute sedation | ↑ | ||
Electroencephalogram (EEG) activity | ↑ | ||
Sedation | ↑ | ||
Postural sway | ↑ | ||
Psychomotor effect | ↑ | ||
Sedation | ↑ | ||
Thiopental | Anesthesia | ↔ | |
Sedation | ↑ | ||
Others | Impaired gastric emptying | ↔ | |
Adverse effects | ↑ | ||
Sedation | ↔ | ||
↔ = unchanged; ↑ = increased; ↓ = decreased. * Older adults are particularly susceptible to the hypoglycemic action of glucose-lowering drugs. Hypoglycemia may be difficult to recognize in older adults. | |||
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. | |||
