Drug Interactions

with William Sala, M.D., internal medicine specialist, Columbia St. Mary’s

Last Updated: July 1, 2003

Seniors in the United States currently account for 13% of the population. However, they consume about 30% of prescription medication and 50% of over-the-counter drugs. So it’s no surprise that 15% of senior hospitalizations are due to adverse drug effects.

As we age, we generally suffer from more ailments that respond to drugs ranging from arthritis-strength pain relievers to the new statin drugs to control cholesterol.

William Sala, M.D., internal medicine specialist, Columbia St. Mary’s "Generally speaking, the older a person is the more likely it is that they are on many medications due to more medical problems. Literature suggests that elderly persons taking nine or more pills or more than twelve doses of medicine a day are at a greater risk of drug reactions or interactions."

"Literature suggests that elderly persons taking nine or more pills or more than twelve doses of medicine a day are at a greater risk of drug reactions or interactions. And the older you are the more likely it is," said Dr. William Sala, an internal medicine specialist with Columbia St. Mary’s.

The aging metabolism
Another cause of drug reactions among seniors is changes in the body as it ages. These changes affect absorption, distribution, metabolism and excretion of drugs.

Absorption, or how well the drug is taken into the body, is generally the least affected although, for example, changes in the PH level in the stomach may affect the speed at which a drug is absorbed.

Distribution is definitely affected by aging. As the body ages, the muscle mass and water content decreases while the amount of fat increases. As a result, a fat-soluble drug will take longer to eliminate.

For example, a normal dose of valium in a younger person will take about 24 hours to decrease by half, in the elderly it may take up to 90 hours – a huge difference, and one that can easily result in unwanted side effects such as confusion, unsteady gait and, in extreme cases, lethargy.

Drugs that are metabolized by the liver are also affected by aging, becoming more or less effective. If they are metabolized too quickly, the patient will not see a therapeutic effect. If too slowly, they can become toxic as they build up in the system.

Renal excretion is also highly affected by aging. "Generally, kidney function decreases by 50% between ages twenty-five and eighty-five," Doctor Sala said.

The main overdose or reaction problems in people with renal dysfunction occur with drugs with a narrow therapeutic index – drugs which are toxic at doses very close to the therapeutic ones.

This is why drugs with narrow windows are always closely monitored until the correct dose is established for individual patients. This also explains why someone who has tolerated a drug for years may start showing side effects from it if their renal function is decreased.

A common drug reaction
One of the most common problems for seniors is pain. The usual remedies – aspirin and ibuprofen – can cause problems in some individuals, particularly if taken at high doses over longer periods of time.

"These drugs can affect the kidneys in such a manner as to cause high blood pressure, renal failure and, in those already at risk for congestive heart failure, actually exacerbate the problem. Even the COX-2 inhibitors can cause some gastrointestinal bleeding or renal failure. Generally most of these problems promptly resolve themselves when the offending drug is discontinued," Dr. Sala said.

Dr. Sala noted that of the pain relievers, acetaminophen is the best tolerated by most people. "It is safe up to one gram three times a day and studies have shown it has great analgesic properties. I prefer to start my patients on this," the doctor said.

Monitoring drugs
Dr. Sala attributes many drug reactions to the fact that it isn’t easy to remember to take too many medications on schedule. To aid in prescription scheduling, he recommends a seven-day pillbox with compartments for morning, afternoon and evening medications. In that way, patients or family members need only sort the pills once a week, and the danger of doubling a dose is greatly diminished.

In addition, seniors and family members should acquaint themselves with the side effects of each medicine, especially new ones.

Dr. Sala stresses that it also is important to review all medications, including over-the-counter and dietary supplements, at every doctor’s appointment and to bring the actual bottles to the office.

"I find it useful to actually review the medications each time I see a patient and to talk about the risks associated with supplements and over-the-counter medications and from drug interactions," the doctor said.

"If a new drug is introduced, I follow it very closely. I try to follow the motto – one disease, one drug, once a day – whenever possible," he concluded.

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