As we grow older, we become more sensitive to medications and may experience adverse drug reactions or increased side effects. Reasons for this include:
Increased risk of chronic illness. Older adults are more likely than any other age group to have one or more chronic illnesses, including heart disease, high blood pressure, diabetes, and arthritis. With some chronic medical conditions, the body may metabolize drugs less effectively.
Multiple medications. Because 30% of prescription drugs are dispensed to people over 60 years of age, it is not unusual for an older person to be taking five or more medications sometimes several times per day. The more medications a person takes, however, increases a risk for interaction with other medication, food, or alcohol. Risk of adverse drug effects increases dramatically with each additional drug.
Complex dosage schedules. When multiple medications are taken at different times each day, dosage schedules can often be complicated. This complication increases the risk of making a mistake, for example, taking a dose twice or forgetting to take a medication when prescribed.
Types of medication. Older adults are more likely to be taking medications that have greater potential for causing adverse reactionsfor example, cardiac, diuretic, antihypertensive, anticoagulant, and central nervous system depressant medications.
Age-related changes. With age, there are certain physiological changes that can affect the way drugs interact with the body. Normal aging can alter the way drugs are absorbed, metabolized, distributed, and removed from the body.
Physical Changes That Affect How Drugs Act
Increase in Percentage of Body Fat
As a person ages, the ratio of lean body mass to body fat tissue changes. Although total weight may remain the same, the percentage of body fat does increase.
Result: Drugs distributed in fat have a broader and prolonged distribution. In other words, some medications may remain in the system for a longer period of time.
Decrease in Body Fluid
The percentage of body weight consisting of water decreases as an individual ages.
Result: Drugs may become more highly concentrated, possibly exaggerating the medication’s effect. Reducing the medication dosage can prevent this problem.
Decrease in Action of the Gastrointestinal Tract
The emptying of the stomach slows down and food moves through the intestines at a slower rate, as we grow older.
Result: The action of a medication may be decreased or delayed. Usually this change does not present a significant problem.
Decrease in Liver Function
As individuals age, the liver decreases in size, blood flow to the liver decreases, and enzymes (in the liver) that break down medications decline.
Result: Drugs can collect in the liver, causing toxicity. Reducing dosage can prevent this problem.
Decrease in Kidney Function
Similar to the liver, changes in kidney function occur as we age. The kidneys often become smaller, blood flow to the kidneys decreases, and our kidneys become less effective at filtering toxins. Certain medical conditions such as heart failure, anemia, or dehydration may also contribute to impaired kidney function.
Result: Medications are filtered through the kidney more slowly; therefore these drugs may remain in the kidney for longer periods of time.
In general, older adults should approach medications differently than young and middle-aged individuals.
- Taking multiple medications at varying times increases the likelihood of making a mistake. Older adults taking more than one medication may consider using medication reminders such as daily or weekly pill dispensers or color-coded regimens to assist them with taking their medication as prescribed.
- Age-related physical changes can lead to greater drug sensitivity and exaggerated effects. Seniors need to practice caution and pay close attention to the types and amounts of medication they take. Asking specific questions to one’s physician AND pharmacist can help to reduce the chance of unnecessary drug reactions.
- Due to these age-related changes, the action of a drug may be less predictable than it is in a younger or middle-aged person. Therefore, the standard adult dose of some drugs may be altered or even reduced.
Senior Series Volume 2, The Center on Rural Elderly, University of Missouri System.