Aging & Health A to Z
Basic Facts & Information
Most older people take several medications for the treatment of chronic illnesses. Medicines are also sometimes used to prevent many diseases of older adults. People 65 years old and older are prescribed medications more frequently than any other age group in the United States.
Why Medications Work Differently In the Older Adult
For medications to be successfully used, the correct drug must be administered for the correct condition, for the correct patient, and at the right dose for the right period of time. Unfortunately, this is not always easy. Many factors influence drug treatment. For example, a person may be on medications for other conditions, in addition to the one currently being treated. This could result in the new drug not working the way it should, or there may be an interaction between the various medications.
Medication dosages are generally determined by clinical trials done in relatively young, healthy people. These dosages may not be appropriate in older adults because changes associated with age can affect how our bodies deal with drugs. This in turn can affect how the drug works as well as the appropriate dosage. These age-related changes include changes in metabolism and body composition, as well as in the effects of conditions that develop as we age and the medications we take for these conditions.
Changes in the Body
To work effectively, medications must be:
- absorbed into the body (usually through the stomach and intestines)
- distributed to where they are needed
- metabolized (chemically changed for elimination from the body)
- eliminated from the body (usually through the urine)
Changes in the body as we age can affect any of these factors. For example, weight gain often occurs with age, while muscle mass decreases. This affects how medications are distributed to different parts of the body. Liver and kidney function also decrease with age, which can slow down drug metabolism and elimination from the body.
These bodily changes associated with aging can change the appropriate dosage for any particular person. When age-related changes decrease absorption or distribution of the drug, a higher dosage may be needed. On the other hand, age-related changes that decrease drug metabolism and elimination may mean that a lower dosage may reach the same effect.
Older adults often have more than one medical condition at the same time. This can affect how dugs are absorbed, eliminated, or metabolized. For example, liver or kidney disease may slow down drug elimination, which is why lower dosages are often prescribed for patients with these conditions. Obesity and diseases that cause fluid retention also change drug distribution. Older adults with memory problems may have increased sensitivity or unusual reactions to certain drugs.
Food or Medications
Medications can also be affected by food and other drugs that are being taken at the same time. For example, some antibiotics are not absorbed as well when they are taken with things that contain a lot of calcium, magnesium, or iron (such as antacids, vitamins, or dairy products).
Some drugs can slow down the metabolism of other medications, while others can speed up the process. And certain foods, such as grapefruit juice, can also slow down the metabolism of medications, making the medication build up in the body.
Different medications can also interact with each other, sometimes with serious consequences. When drug interactions happen, dosages of a new medicine that are usually correct may be too high or too low. Also, if a new drug interacts and slows down the metabolism of a drug that you are already taking, you may begin to have side effects without having had these problems before.
You should read all prescription labels carefully for warnings on how to take the medication, what it should or should not be taken with, and the potential for drug interactions. Ask your healthcare professional if you have any questions or concerns on potential interactions.
Other factors also affect how the body deals with medications. For example, cigarette smoking, caffeinated or alcoholic beverages, changes in diet, and viral infections seem to affect drug metabolism.
Updated: March 2012
Posted: March 2012