By: Sheri Waldrop
As a nation, we are aging. By the age of 65, two-thirds of us take one or more medications a day—and a lot of us take as many as three.
With roughly 20 percent of people over the age of 65 having diabetes and many in this group taking medication to control it, are there special concerns for this age group?
According to experts, the answer is “yes,” albeit a qualified one since aging is a unique process for each of us.
Each Person Responds Differently to Medication
Karen George, RN, CDE, of Baylor University’s Diabetes Center in Dallas, Texas, notes that “a person of 80 may respond physiologically like a person of 60, while another person that age may be completely different.”
We are still learning about how older people respond to diabetes medications. As you age, less blood flows to your organs, including the kidneys, liver and gastrointestinal tract. Medication absorption slows down as well.
In addition, as we grow older, our activity level and diet may change, and other disease states—such as congestive heart failure or kidney disease—can have an even stronger effect on how we handle medications.
Until recently, there weren’t many studies on aging and its effects on medication metabolism. In the past, when drug companies developed new medications, the majority of clinical trials used subjects younger than 75, while others limited the percentage of patients over age 65.
“This means that, for all practical purposes, the elderly were a ‘minority’ in clinical drug trials—and there is still much to learn about how medications affect this age group,” says Linda Jaber, PharmD, professor of pharmacy at Wayne State University in Detroit, Michigan.
Changes in Bioavailability
Many factors affect how long medication lasts in your body, how it is distributed, how the liver metabolizes it, and how it is excreted by your kidneys. With advancing age, all of these factors change to some degree.
As we age, blood albumin levels decrease by as much as 15 to 25 percent. This can affect medications, including some diabetes medications that bind to protein (albumin), by lowering the amount of medication that is absorbed. For that reason, the chance of hypoglycemia (low blood glucose) increases in people with diabetes.
“The sulfonylureas, and repaglinide (Prandin) and nateglinide (Starlix), will see the greatest effect,” says Jaber. “With them, it’s better to start low and slowly increase the medication. But in general, this isn’t a clinically significant factor—just an area to be aware of.”
Your liver metabolizes medications into forms that can be excreted from the body. By the age of 65, blood flow through the liver declines by roughly 40 percent. With less blood flowing through the liver, less medication is being passed through it to be broken down.
Jaber notes that medications that are metabolized mainly by the liver—including several diabetes drugs—should be given with caution, “and liver function should be assessed regularly in the older client.”
Kidney function also changes as we get older. The glomerular filtration rate (GFR)—the rate at which our kidneys filter blood—decreases by approximately 1 percent per year after age 40 in two-thirds of older adults. Some conditions, such as chronic hypertension, can accelerate this decline.
However, according to Barbara McClosky, PharmD, BCPS, CDE, and manager of the Diabetes Center at Baylor Medical Center in Irving, Texas, unless there is underlying kidney failure, the effect on the person usually is insignificant.
“Changes in kidney function are very gradual changes and usually do not affect how medications are prescribed,” she states. “But there are some medications that people can be more sensitive to because of decreased kidney function. This includes sulfonylureas, which are excreted by the kidneys.”
McClosky adds that serum creatinine level, a test used to check kidney function, can be misleading in the older person.
“With aging, muscle mass decreases. Since creatinine is a by-product of muscle breakdown, in the older person a ‘normal’ serum creatinine level could mean lowered kidney function, since we produce less creatinine to clear. Instead, the 24-hour creatinine clearance is a better test for measuring kidney function in the older person.”
Glucophage (metformin) is a diabetes medication that warrants caution in the older person if kidney function changes. One reason is the risk of lactic acidosis if the person can’t excrete the medication.
“I am especially careful to monitor kidney function in my older clients if they are on this medication,” says Philip Levin, MD, an endocrinologist and director of the diabetes program at Mercy Medical Center in Baltimore, Maryland.
While the manufacturer recommends that Glucophage not be prescribed for those over age 80, this medication does have the advantage of lowering the risk of hypoglycemia when used alone.
“This may make it a good choice in those ‘physiologically younger’ older clients with good kidney function as measured by a 24-hour creatinine clearance,” says Dr. Levin.
Drug Interactions: Multiple Medications a Growing Concern
Side effects from medications can include symptoms such as confusion, nausea, poor balance, change in bowel patterns, or sleep changes. These side effects may be mistaken for illness or “senility,” and then even more medications may be prescribed to treat the “illness”—thus compounding the problem.
As a person ages, the chance of having an adverse drug reaction increases. Some experts estimate that 3 to 10 percent of all hospital admissions of the elderly may be caused at least in part by adverse drug effects.
Taking multiple medications can make it difficult to determine exactly which one is causing side effects. Condit Steil, PharmD, CDE, associate professor at McWhorter School of Pharmacy at Samford University in Alabama and director of the Center for the Advancement of Pharmaceutical Care Development in Community, recommends introducing medications one at a time when possible. “Then, if adverse effects occur, you know which one is causing them,” he says.
Cardiac problems in the elderly may also mean that caution is needed when prescribing certain medications.
“Sensitizers such as Actos and Avandia can cause edema in an elderly person, especially if there is any heart failure present,” says Catherine Lindblad, PharmD, clinical assistant professor at the Institute for the Study of Geriatric Pharmacotherapy at the University of Minnesota College of Pharmacy. “For the first six months after starting on [these medications], a person needs to be carefully evaluated for edema and any other symptoms of heart failure—including sudden weight increase—along with liver function.”
Aging and the Risk of Hypoglycemia
Aging can increase the risk of hypoglycemia for several reasons. One is a change in our counter-regulatory response to hypoglycemia as we age.
“In the older person, the responsiveness of glucagon and epinephrine to changes in blood glucose is lessened,” Jaber explains. “If the person is taking medications that stimulate the release of insulin, there is a slightly higher risk of hypoglycemia. Hypoglycemic unawareness can also be aggravated in this age group, especially with long-standing diabetes.”
This risk of hypoglycemia un-awareness increases if the person is also being treated with beta blockers, which may mask some of the symptoms of low blood glucose.
Dr. Levin is aware of this risk.
“In general, the older the patient, the lighter the dose, because of the concern about potential problems, especially hypoglycemia,” he advises. “This is especially true for the older person with irregular eating habits, and it can definitely affect the type of medications prescribed.”
Good control is always the goal, though, and Dr. Levin and others note that while medications may be introduced cautiously in this age group, they are increased slowly until good control is achieved—without hypoglycemia.
Eating Patterns Affect Medications
Sometimes an older person with diabetes has irregular eating patterns. The reasons can range from budgetary problems to a diminished appetite. In this case, it becomes especially important to discuss eating habits with your healthcare provider or diabetes team.
Dr. Levin takes eating patterns into account when prescribing medications for his older clients.
“For instance, the thin elderly lady with type 2 diabetes who ‘nibbles’ or sometimes skips meals may do better with some of the new medications with a quick onset and quick end of action, such as Starlix or Prandin. I would give her a small amount to start with and suggest, ‘If you eat, take it; if you don’t eat, don’t take it.’ This can also help with remembering when to take it: Just take it when you eat.”
Insulin Use by Older People
Lindblad notes that insulin also carries a risk of hypoglycemia for the elderly.
“While insulin gives good control [for the older type 2], it also has the highest risk of hypoglycemia. For this reason, the risk of hypoglycemia versus good control needs to be taken into consideration in this age group.”
At times, health professionals are cautious about starting insulin in older clients with diabetes, a concern that isn’t always warranted, says Dr. Levin.
“In practice, my older clients normally do very well. I will often start with a low dose, if it’s needed for good glucose control, then increase it slowly to see how the person responds—and to prevent lows, which could be dangerous in this age group. If the person is on medications such as beta blockers, which can blunt the symptoms of hypoglycemia, I’m especially cautious. But normally there isn’t a problem.”
Karen George has recently seen a new trend in insulin dosing for older clients. “We’re seeing more older clients with type 1 diabetes on insulin pumps. This is exciting, since people are staying healthy and active later into life.”
Dr. Levin agrees that advances in pump technology have opened up the use of the pump to more people, including older clients.
“There is a lot more fear about prescribing [pumps] for this age group than is justified,” he says. “I have several older clients in their late 60s on pumps who have benefited greatly. This is especially true for the type 1 who has battled diabetes and frequent hypoglycemic reactions. They can of-ten obtain good control with a pump.”
Steil notes that older people may at times unknowingly take over-the-counter medications that could affect their diabetes.
“These include cold medicines and cough medication that can increase glucose levels slightly.”
Because of the effect these medications can have, it’s important to always let your doctor and pharmacist know about all the medications you are taking, including over-the-counter ones.
Be Your Own Advocate
Becoming your own advocate is vital if you are an older person with diabetes who is taking medication.
“An older person with diabetes might be seeing several physicians for different problems, and they might not communicate with each other,” George says. “They may prescribe the same medication by a different name, and the person doesn’t even know they are receiving a double dose.
“If you have all your medications filled at one pharmacy, your pharmacist will pick up on things like this, but if you fill your prescriptions at different pharmacies, this can be missed.”
George stresses the importance of giving a complete written list of all medications you are taking to both your physician and your pharmacist.
The U.S. Food and Drug Administration (FDA) has now asked that older subjects be included in clinical trials for new drugs. Today, almost every drug that comes through the FDA has been examined for its effects on the elderly.
Trends in treating diabetes in the older person are changing, with the advent of new medications and options. Whether this treatment is an insulin pump or oral medications whose dosage and type may partially depend on your age and how you respond to them, improved diabetes control is always the goal.
Clinical adviser’s note: Prandin (repaglinide) is highlighted by Dr. Levin for two safety factors: its short action and the fact that it needs to be taken only if and when a meal will be eaten, thereby lowering the risk of hypoglycemia in the elderly or anyone with erratic eating patterns. Prandin also has an additional property that makes it ideal for the elderly or anyone with im-paired kidney function: it has no significant kidney excretion and therefore may be the insulin secretagogue drug of choice for someone with mild to moderate renal failure.