Drugs and Aging
Older people tend to take more drugs than younger people because they are more likely to have several, often chronic disorders. On average, an older person takes four or five prescription drugs and two over-the-counter drugs each day. Also, older people are more than twice as susceptible to side effects of drugs as younger people (see Section 2, Chapter 15). Side effects are also likely to be more severe, affecting quality of life and resulting in visits to the doctor and in hospitalization.
As people age, the amount of water in the body decreases and the amount of fat tissue relative to water increases. Thus, in older people, drugs that dissolve in water reach higher concentrations because there is less water to dilute them, and drugs that dissolve in fat accumulate more because there is relatively more fat tissue to store them. Also, as people age, the kidneys are less able to excrete drugs into the urine, and the liver is less able to metabolize many drugs (see Section 2, Chapter 11). Because of all these age-related changes, many drugs tend to stay in an older person's body much longer than they would in a younger person's body, prolonging the drug's effect and increasing the risk of side effects. For these reasons, older people need to take smaller doses of certain drugs or perhaps fewer daily doses. Also, other, safer drugs can often be substituted.
Older people are more sensitive to the effects of many drugs. For example, older people tend to become sleepier and are more likely to become confused when using sleep aids or antianxiety drugs. Drugs that lower blood pressure by widening (dilating) arteries and reducing the amount of work the heart has to do tend to lower the pressure much more dramatically in older people than in the young.
Many commonly used drugs, such as some antidepressants and diphenhydramine (used in the treatment of insomnia), have anticholinergic effects. Older people are particularly susceptible to these effects, which include confusion, blurred vision, constipation, dry mouth, light-headedness, and difficulty with urination or loss of bladder control. Some anticholinergic effects, such as reduction of tremor (as in the treatment of Parkinson's disease) and reduction of nausea, are desirable, but most are not.
Drugs may produce a side effect because of interaction between the drug and a disease other than the one for which the drug is being taken (drug-disease interaction) or between the drug and another drug (drug-drug interaction), food (drug-food interaction), or a medicinal herb (drug-medicinal herb interaction (see Section 2, Chapter 19)). Because older people tend to have more diseases and to take more drugs than younger people, they are more likely to have drug-disease and drug-drug interactions. Patients, doctors, and pharmacists can take steps to reduce the risk of these interactions (see Section 2, Chapter 13).
Not following a doctor's directions for taking a drug (noncompliance or nonadherence) can be risky (see Section 2, Chapter 16). Old age alone does not make a person less likely to take drugs as directed; however, 40% of older people do not do so. Not taking a drug, taking too little, or taking too much can cause problems. Taking less of a drug because it causes side effects may seem reasonable, but people should talk to a doctor before they make any changes in the way they take a drug.
See the table Some Drugs With Increased Risk for Older People.
See the sidebar Anticholinergic: What Does It Mean?
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