Chapter VI DRUG THERAPIES FOR THE
ELDERLY CLIENT
DRUG THERAPY IN THE ELDERLY
PHYSIOLOGIC CHANGES AFFECTING DRUG ACTION
As a person ages, gradual changes occur in the human physiology. Age-related changes may alter therapeutic and toxic effects of drugs.
1. BODY COMPOSITION
Proportions of fat, lean tissue and water in the body change with age. Total body mass and lean body mass tend to decrease. The proportion of body fat tends to increase. Varying from person to person, these changes in body composition affect the relationship between a drug’s concentration and solubility in the body. For example, a water-soluble drug, such as gentamicin, is not distributed to fat. Since there is relatively less lean tissue in an elderly person, more drug remains in the blood, and toxic levels can result. Likewise, pentobarbital, which is distributed to fat, may produce lower levels.
2. GASTROINTESTINAL FUNCTION
In the elderly, decreases in gastric acid secretion and gastrointestinal motility, slow the emptying of stomach contents and movement of intestinal contents through the entire tract. Furthermore, although inconclusive, research shows the elderly may have more difficulty absorbing medications. This is a particularly significant problem with drugs having a narrow therapeutic range, such as digoxin, in which any change in absorption can be crucial.
3. HEPATIC FUNCTION
The liver’s ability to metabolize certain drugs decreases with age. This is probably due to diminished blood flow to the liver. This results from the age-related decrease in cardiac output. When an elderly patient takes certain sleep medications, such as secobarbital, his/her liver’s reduced ability to metabolize the drug, may produce a hangover effect due to central nervous system depression. Elimination of these medications is highly dependent on the liver.
Decreased hepatic function may cause:
- More intense drug effects due to higher blood levels
- Longer-lasting drug effects due to:
Prolonged blood concentrations
- Greater incidence of drug toxicity
4. RENAL FUNCTION
Most elderly persons’ renal function is usually sufficient to eliminate excess body fluid and waste. However, his/her ability to eliminate some medications may be reduced by 50% or more.
Many medications commonly used by the elderly, such as digoxin, are excreted primarily through the kidneys. If the kidney’s ability to excrete the drug is decreased, high blood concentrations may result. Digoxin toxicity, therefore, is relatively common.
Drug dosages can be modified to compensate for age-related decreases in renal function. Aided by laboratory tests, such as BUN and serum creatinine, clinical pharmacists and doctors can adjust medication dosages to provide the expected therapeutic benefits without the risk of toxicity. Patients should be observed for signs of toxicity. A patient taking digoxin, for example, may experience anorexia, nausea and vomiting.
5. ADVERSE DRUG REACTIONS
As compared with younger people, the elderly reportedly experience twice as many adverse drug reactions. This fact might be due to greater drug consumption, poor compliance and physiologic changes.
Signs and symptoms of adverse drug reactions; confusion, weakness and lethargy; are often mistakenly attributed to senility or disease. If the adverse reaction isn’t identified, the patient may continue to receive the drug. Furthermore, he/she may receive unnecessary additional medications to treat complications caused by the original medication. Although any medication can cause adverse reactions, most of the serious reactions in the elderly are caused by a relatively few medications: diuretics, digoxin, corticosteroids, sleep medications and nonprescription drugs. Patients who take these drugs should be carefully observed for toxicities.
Diuretic toxicity
Because total body water decreases with age, normal doses of potassium wasting diuretics, such as hydrochlorothiazide and furosemide, may result in fluid loss and even dehydration in the elderly patient. These diuretics may deplete serum potassium, causing weakness in the patient; and they may raise blood uric acid and glucose levels, complicating pre-existing gout and diabetes mellitus.
Digoxin toxicity
As the body’s renal function and rate of excretion decline, digoxin concentrations in the blood may build to toxic levels, causing nausea, vomiting, diarrhea and most serious, cardiac arrhythmias. Severe toxicity may be prevented by observing the patient for early signs such as appetite loss, confusion or depression.
Corticosteroid toxicity
Elderly patients on corticosteroids may experience short-term effects including fluid retention and psychological manifestations ranging from mild euphoria to acute psychotic reactions. Long-term toxic effects, such as osteoporosis, can be especially severe in elderly patients who have been taking prednisone or related compounds for months or even years. To prevent serious toxicity, especially observe for subtle changes in appearance, mood, mobility, as well as for signs of impaired healing and fluid and electrolyte disturbances.
Sleep medication toxicity
In some cases, sedatives or sleeping aids, such as flurazepam, cause excessive sedation or residual drowsiness.
Nonprescription drug toxicity
When aspirin and aspirin-containing analgesics are used in moderation, toxicity is minimal, but prolonged use may cause gastrointestinal irritation and gradual blood loss resulting in severe anemia. Although anemia from chronic aspirin consumption can affect all age groups, the elderly are most vulnerable to it because of their already reduced iron stores.
Laxatives may cause diarrhea in elderly patients who are extremely sensitive to drugs such as bisacodyl. Chronic oral use of mineral oil as a lubricating laxative may result in lipid pneumonia due to aspiration of small residual oil droplets in the patient’s mouth.
Patient noncompliance
Approximately one third of the elderly fail to comply with their prescribed doses or to follow the correct schedule. They may take medications prescribed for previous disorders, discontinue medications prematurely or use PRN medications indiscriminately.
The medication regimen should be reviewed with him/her. The patient must clearly understand the dose and the time and frequency of doses. Also, he/she should know how to take each medication, that is, with food or water or by itself.
The patient should be given whatever help is necessary to avoid drug therapy problems, and referred to a physician or pharmacist if further information is needed.
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