Drug Effects in the Aging Body

Ron Conte, Pharm.D.

As I realize the ways my own body is aging, I have thought about how both the desired and undesired effects from drug therapy may be altered. For example, if I take an antihistamine for my seasonal allergy, will I get the same effects as when I was in my 30’s? At my age now, will there be more exaggerated side effects, more harmful effects than when I was younger?

The effects of some drugs do change from the time we are infants to adolescence, then from young adulthood to midlife, and finally as older adults. The World Health Organization (WHO) has gratefully classified the elderly into a few categories: “young” old are the years from 60 to 80 while 80 to 100 years of age are referred to as the “oldest” old.

Those who reach 100 years of age and beyond are classified as “centenarians”. I use the word ‘gratefully’ because I am still classified as “young” old.

The desired effects from drugs are dependent upon many processes within the human body. As we age, some oral meds may not be adequately absorbed. The aging blood (circulatory) system may not be able to transport a med in sufficient amounts.

Various organ systems, e.g., lungs, liver, kidneys, etc., may not be able to accept or eliminate a med efficiently. With any of these organ systems having moderate to severe dysfunction, drug effects may be altered. These and additional changes in body systems as we age are known as geriatric pharmacokinetics.

If you remember my 2018 article about A Drug’s Journey Through the Human Body, the journey includes drug absorption, metabolism, distribution, and elimination processes. Changes as we age in any of these processes are unique for each of us. In addition, it is well known that stressors to the body accelerate decline in function of various body systems.

The more common stressors are illnesses, medications, significant life changes, and sudden changes in physical demand. No one stressor alone will determine how the body will age. Let me provide you with single examples of these stressors:

Illness: with kidney dysfunction, toxins and drugs may not be adequately eliminated from the body, causing harm or cell death to other systems

Medication: some drugs decrease blood (white) cells as a side effect, making it more difficult to ward off harmful bacteria and viruses; resultant infections may be severe enough to decrease one’s lifespan

Significant Life Change: death of a loved one is one example; from my personal experience, my dad died just three months after my mom had passed

Sudden Changes in Physical Demand: those of us who choose to exercise vigorously after months to years of no exercise, are at risk of causing more harm to our bodies; best to start with moderation

There are hundreds of examples of how stressors may modify a lifespan. But let us also keep in mind how body systems do age over a lifetime. At the age of thirty, the heart is capable of pumping ten times more than what is usually needed daily. Each year thereafter, that reserve decreases by 1%.

Liver cells over decades do not work as effectively as when we are younger. This usually results in protracted drug metabolism and more drug toxicity for older adults. Many drugs are stored in body fat then released over time.

From 25 to 75 years of age body fat may double. Therefore, drug amounts released from fat tissue may be slower resulting in a longer duration of drug effects including side effects.

As for muscle mass, most of us will experience a decrease in our twilight years. This results in a corresponding decrease in body weight. And, since many drug dosages are weight-based, a dosing regimen may need to be decreased as we age.

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Due to limited column space, I have barely touched the surface of this topic. If you seek additional information on this or any drug topic, you may contact me at my email address: rrxconte@gmail.com