How Aging Affects Drug Absorption
A guide to helping older adults avoid harmful drug effects
Perhaps you’re feeling frustrated because you can’t remember things. Or you find yourself exhausted after doing simple chores. Maybe you figure this is a normal part of aging as you move through your 60s, 70s, and beyond. But these and other symptoms could be side effects of medication you’ve taken routinely for years—only now they pose a problem as you reach older ages and your body changes the way it processes drugs.
Age-related changes in physiology, including metabolism, can make older adults prone to a tangle of medication issues: Some drugs might not be as powerful, some might pack an extra punch and raise the risk of toxicity, and some may cause side effects.
“All older people are at higher risk for medication-related problems. The risk is even greater when you are on a number of medications,” says Peggy Soule Odegard, PharmD, CDE, professor of pharmacy and associate dean at the University of Washington School of Pharmacy in Seattle.
Medha Munshi, MD, director of the Geriatric Diabetes Program at the Joslin Diabetes Center in Boston, urges patients 65 and older, and their caregivers, to be alert to possible drug-related problems, which can be mistaken for signs of growing old.
“Too often people think, ‘I’ve been on this medication for years, so it can’t be the cause,’ ” Odegard says. But even a longtime prescription may turn troublesome as you get older.
Due to physiological changes, plus the presence of chronic conditions, every older body truly is unique. So the correct dose of any oral medication depends on what’s happening in your own body. For many medications, the dose you need decreases over time and may be half of what you took in your 40s or 50s. Likewise, when starting a new medication, the initial dose may be less than half of the starting dose for a middle-aged person.
Here’s what generally happens as an aging body processes drugs:
Metabolism slows. Once in the body, medications travel to the liver, where many are metabolized or processed (though some are metabolized in the kidneys). The liver filters out much of the medication before releasing the rest into the bloodstream. It also chemically modifies drugs to permit elimination from the body. Because aging can bring decreases in enzyme activity, reducing the ability to break down and filter out drugs, more medication can remain in the bloodstream.
Elimination declines. The kidneys filter your blood, removing some drugs from the body through the urine. Kidneys function more slowly and less efficiently with age, so more of the drug remains in your system, and medication levels build. “With older patients, the critical system is the kidneys,” Odegard says. “For medications that rely solely on the kidneys for their elimination, you run the risk of having toxicity at the same dose you took when you were younger.” Kidney disease further reduces elimination of medications, potentially raising the risk for toxicity. That’s why people with kidney disease may require lower doses of medications and, in some cases, will even be prescribed a drug that doesn’t rely on the kidneys for elimination.
Because insulin is partly cleared by the kidneys, reduced kidney function can affect insulin levels: Decreased elimination from the body means insulin’s effects may last longer than usual. “That change is gradual … and would mostly be accounted for over the many months and even years that patients are using and adjusting their insulin,” says Craig Williams, PharmD, a pharmacist and professor at Oregon Health and Science University. But insulin doses may need to be adjusted in the short term when there’s a sudden decline in kidney function.
Drug effects increase or linger. The bloodstream delivers medication throughout the body. As you age, the amount of water in your body decreases, and body fat increases. So drugs that dissolve in water reach higher concentrations—they’re literally less watered down—and have greater effect. Drugs that dissolve in fat are distributed in greater volume, leading to an accumulation that makes the drug last longer.
What Could Go Wrong?
You play the leading role in medication safety. Contact your prescribing doctor or pharmacist if you suspect any of the following problems:
Side Effects. The risk and severity of side effects increases with age. For example, a statin prescribed to control cholesterol levels may be more likely to cause muscle aches in older adults. Beta blockers, which control blood pressure to prevent stroke and heart attack, can make it hard to detect low blood glucose. These drugs control the release of adrenaline, the hormone that creates the shaky sensation of hypoglycemia. In effect, they mute the body’s natural warning system. “If you’re on beta blockers, you have to be in touch with other signs of hypoglycemia, like feeling hungry, and be more diligent about checking your blood glucose throughout the day,” Odegard says.
Toxicity. When too much of a medication accumulates in your body, it might become poisonous. Depending on the drug, toxicity may cause symptoms similar to a side effect or something more severe, including organ damage—or a life-threatening overdose. For example, blood pressure medication may need to be reduced with age to prevent blood pressure from going too low, which can present as dizziness or light-headedness.
Drug interactions. One medication potentially can alter the effect of another, either reducing its effectiveness, making it toxic, or creating side effects. Over-the-counter meds, dietary supplements, and certain foods also can cause an interaction (see “Medication Interactions,” below).
The average older adult comes to Munshi with diabetes, assorted related ailments, and a list of 11 to 14 medications. Each additional prescription increases the risk of a medication problem, including drug interactions and adverse drug events, she says.
After seeing her patients struggle with numerous prescriptions, Munshi eventually concluded that the more complex the regimen, the more difficult it is for an older person to succeed at self-care. Now she strives to simplify treatment plans by eliminating nonessential medications, such as those that counter a mild side effect or provide minimal benefit.
Munshi and Odegard say your physician should monitor your medications and make adjustments, if necessary, at least once a year. They also made these suggestions:
- Use one pharmacy for all prescriptions. The pharmacist can help monitor your medications for drug interactions.
- Give each provider a list of your medications. Note the dose, and include over-the-counter drugs and dietary supplements. Discuss the list at every appointment.
- Understand your meds. Read the product information and ask questions so you understand the condition it treats, how and when to take it, and the possible side effects.
- Beware of dietary supplements. The Food and Drug Administration warns that using supplements with prescription or over-the-counter drugs could be dangerous. Ask your pharmacist which are safe to take with your meds.
- Speak up. Tell your provider and pharmacist if you suspect side effects or have other concerns.
Symptoms of side effects, drug reactions, and drug interactions include:
- memory loss
- blurred vision
- muscle aches and weakness
If you’re experiencing any of these problems, talk to your health care provider.
Prescription drugs. Every medication, including insulin, has potential for trouble when combined with certain other prescription meds. Among oral type 2 drugs, sulfonylureas, thiazolidinediones, meglitinides, and DPP-4 inhibitors are most susceptible.
Over-the-counter medications. Many antihistamines, common in nighttime pain-relief formulas, cough and cold remedies, and allergy drugs, have a sedating effect. If combined with a prescription sleep aid, they may cause drowsiness, dizziness, or unsteadiness that could lead to falls.
Dietary supplements. Melatonin, a natural hormone that helps regulate the sleep-wake cycle, may be useful for insomnia, jet lag, and other sleep disorders, but it also may increase blood glucose and interfere with diabetes drugs. Ginkgo biloba, used to improve memory, can alter the actions of medicines metabolized through the liver, including blood thinners and diabetes drugs.
Food. Alcohol can change the effect of many medications or cause a range of side effects. Milk products can neutralize the effect of many antibiotics. Grapefruit juice, which interferes with processing by the liver, can lead to higher medication levels in the bloodstream of certain drugs, such as statins.