How Age Increases the Risk for Medication Side Effects

As we age, changes in our body can affect the way medications are absorbed and utilized. We become more sensitive to medications, and we are more likely to experience increased side effects, drug interactions, and other adverse drug reactions.

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Effects of Medication Types, Interactions, and Dosing Schedules

Older adults are more likely to have one or more chronic illnesses, such as high blood pressure, high cholesterol, type 2 diabetes, coronary artery disease, arthritis, chronic obstructive pulminary disease (COPD), depression, etc. These chronic medical conditions may be treated with multiple medications, creating issues that drive up the risk of side effects. These issues can be related to the following:

Types of Medication: It is not uncommon for older adults to suffer from multiple related chronic conditions. For example, many older adults with type 2 diabetes also have high blood pressure, high cholesterol, and depression.

A typical medication cocktail for this group of people may include an oral diabetes medication (such as Glucophage [metformin]), a blood pressure medication (Diovan HCT [valsartan]), a medication to lower cholesterol (Zocor [simvastatin]) and an antidepressant (Zoloft [sertraline]).

Each type of medication has its own potential side effects, and these can effects add up.

Medication Interactions: Due to the increased risk of chronic illness as we age, many older people may be taking multiple medications. Taking five or more prescription medications is known as polypharmacy, which is associated with adverse medical outcomes. The more drugs you take, the more likely you are to have a drug interaction with other medications, food or alcohol.

Complicated Dosage Schedules: Some medications have specific timing requirements and may need to be taken before a meal, or along with food, or before bed, etc. Taking multiple medications at different times of the day can be complicated and increase your risk of making a mistake. For example, you may forget to take medication at the correct time or you may take a dose twice. You may eat something that blocks its absorption or amplifies its affect.

Effects of the Normal Aging Process

For medications to be effective, they have to be absorbed in to the body (usually through the intestine), distributed in the body to where they are needed (usually via the bloodstream), chemically changed or metabolized (often in the liver or kidneys) and then excreted or removed from the body (mostly through the urine).

The normal aging process can change the way medications are absorbed, metabolized, distributed and removed from the body, causing side effects to become more pronounced. These changes include the following:

Increase in the Percentage of Body Fat

As we age, our bodies have more fat relative to our bones and muscles. Although our weight may remain the same, the percentage of body fat increases while muscle mass decreases. Medications that dissolve in fat may get trapped in your body’s fat cells and remain in your system for a longer period of time even after discontinuing that medication.

Decrease in Body Fluid

You may have heard that the adult human body is comprised of approximately 70% water. In 1945, H.H. Mitchel studied the composition of various organs, and reported that the brain and heart are composed of 73% water, the lungs are about 83% water, the skin contains 64% water, muscles and kidneys are 79%, and even the bones are 31% water.

Muscle cells store more water than fat cells. This means, as we age and lose muscle mass, we also lose some of our water, and are less able to dissolve water-soluble medications. As a result, some medications may become too concentrated in the blood, possibly increasing the medication's effect.

Decrease in Digestive System Function

Digestive system changes as a result of getting older can affect how quickly medications enter our bloodstream. The movements in our stomach slow down, and it takes longer for medications to get into our intestines, where they are later absorbed. Also, our stomachs produce less acid, and it takes longer for some drugs to break down. These changes may cause the action of a medication to be decreased or delayed.

Decrease in Liver Function

The liver is one of the most important organs in our body for metabolizing or breaking down medications. As we age, the liver gets smaller, blood flow to the liver decreases, and the chemicals (enzymes) in the liver that break down medications decline. This can result in medications collecting in the liver, thereby causing unwanted side effects and possible damage to the liver.

Decrease in Kidney Function

Similar to the liver, changes in kidney function occur as we age. The kidneys may get smaller, blood flow to the kidneys may decrease, and they may become less effective at eliminating leftover medications as measured by glomerular filtration rate (GFR). Starting around age 40, kidney function declines approximately 1% each year. As a result, medication stays in the body longer, increasing the effect of the drug and the risk of side effects.

Decrease in Memory

Memory lapses are common in older adults, and as we age, the risk of Alzheimer’s disease and other types of dementia increases. Memory problems can cause people to forget to take medications, which can lead to poor control of their chronic illnesses. Furthermore, people with dementia may not be able to understand or follow a healthcare provider’s instructions, especially related to managing complex medication schedules.

Decrease in Vision and Hearing

Visual problems, such as diabetic retinopathy, glaucoma, and cataracts, are common in older adults and people with eye conditions, causing difficulty in reading labels on prescription medication containers and over-the-counter products. Hearing problems can make it difficult for people to hear instructions from their doctors and pharmacists.

Decrease in Dexterity

Many older people have arthritis, physical disabilities, and nervous system disorders, such as Parkinson’s disease. These conditions can make it difficult to open pill bottles, pick up small pills, or handle medications (eye drops, inhalers for asthma and COPD, and insulin injections).

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