Have you noticed that as you get older you react differently to the medications that your doctor prescribes? Many of us do. In this health alert, Johns Hopkins doctors explain age-related physiological changes that can affect the way our bodies react to medications.
If you’re over 50, chances are you’re taking more medications and in greater quantities than you ever did in previous decades. Indeed, people between the ages of 55 and 64 are given an average of eight different prescription medications during the course of a year. And those over age 70 take an average of 6.5 medications per day. It’s only logical that the more medications you take concurrently, the more likely it is that an adverse drug reaction could occur. And for older people, such risks are further compounded by physiological changes that make the body more sensitive to the effects of medications.
Beginning sometime during our middle thirties and continuing throughout life, measurements of functional capacity of most major organ systems show a gradual decline. Such changes, which are natural and inevitable, do not necessarily have any noticeable effect on one’s quality of life. But they can affect the way that our bodies respond to medications, and make us more susceptible to untoward reactions and side effects of medications.
For one thing, there is an overall decrease in body fluid volume. This results in proportionally higher concentrations of medications or other substances in the bloodstream, thus increasing the risk of toxicity. This effect may be further compounded by an age-related decline in liver and kidney function. These organs are primarily responsible for metabolizing medications and eliminating toxins. Therefore, a decrease in their function means chemical substances remain in the body longer and are more likely to build up to potentially hazardous levels.
Conversely, a sluggish digestive system can slow the rate that medications are absorbed into the bloodstream, meaning that less of the medications is available to produce the desired therapeutic effect. Diminished blood flow to the brain may boost the likelihood that certain medications will cause dizziness, fainting, loss of coordination, forgetfulness, confusion, or other signs of cognitive impairment. In some people the heart functions less efficiently with age, which in turn may deprive other organs of an adequate blood supply, causing further disruptions in how medications are distributed in the body.
Finally, age-associated decrements in vision, hearing, and memory may affect an older person’s ability to properly understand prescription label, package inserts, or doctors' instructions. Bear in mind, however, that chronological age alone is not necessarily a good predictor of the degree of functional decline; there is considerable variability from one person to another in the rate at which such changes occur.
