By William Simonson, PharmD, FASCP, CGP
Vol. 1 No. 4 P. 28
Sheer numbers of medications taken by older adults, often coupled with multiple prescribers, increase the likelihood of detrimental drug interactions.
A drug interaction is defined by the American Heritage Medical Dictionary as “the pharmacological result, either desirable or undesirable, of drugs interacting with themselves or with other drugs, with endogenous chemical agents, with components of the diet, or with chemicals used in or resulting from diagnostic tests.”
With that rather all-inclusive definition, it is obvious that this can be an extremely technical and complex topic. But it can be distilled down to a few important concepts that make the subject of drug interaction more understandable. What drug interactions are, how and why they occur, and ways they can be prevented are subjects of significant importance as related to elders.
Types of Drug Interactions
There are three major categories of drug interactions of primary concern for older adults: drug-drug interactions that occur between prescription, nonprescription, or over-the-counter (OTC) medications; drug-nutrient interactions that occur between a medication and a nutrient provided either in food or a nutritional supplement; and drug-herbal interactions that occur between a prescription or OTC medication and an herbal product.
What makes this topic so complex is that there are thousands of prescription and OTC medications and herbal products. Another confusing factor is that the occurrence of a specific drug interaction is not absolute. That is, the same combination of medications that may result in a harmful interaction in one individual may have little or no effect in another individual.
Mechanisms of Drug Interactions
Drug interactions may occur by different mechanisms. Most oral medications are primarily absorbed into the bloodstream in the first part of the small intestine. Certain medications or nutrients may alter the absorption of one or more medications if taken at the same time. If the medication’s absorption is increased, higher levels of the drug in the body could result in adverse effects. Conversely, if the medication’s absorption is decreased, the beneficial effect of the medication may be minimized or negated.
Taking numerous medications may influence the way one particular medication is eliminated from the body, generally via metabolism in the liver and/or excretion by the kidneys. Decreases in the function of these organs from a health condition or simply the process of aging may influence the level of these medications in the body, possibly resulting in toxicity.
Some medications may interact with certain nutrients, such as calcium, that may inhibit the absorption of the medication into the body, thus diminishing its effect.
Consequences of Drug Interactions
Drug-drug interactions can be life threatening and even lethal. Some of the most serious drug-drug interactions involve the blood thinner warfarin (Coumadin), a product that has the potential to interact with many different products, including aspirin. When an individual is stabilized on warfarin and unknowingly adds aspirin to his or her regimen, a serious bleeding episode can develop due to the effect that the aspirin has on increasing, sometimes dramatically, the anticoagulant effect of the warfarin.
However, most drug interactions are less dramatic in their presentation and may even go unnoticed; yet even minor interactions can have significant consequences. For example, the class of orally administered osteoporosis drugs known as bisphosphonates (e.g., Fosamax, Actonel, and Boniva) are essentially inactivated when they are taken with any nutrients, including juice or coffee.
If an older adult prescribed one of these medications takes it with anything other than water, the potential beneficial effects will be negated. This interaction doesn’t cause any harm or symptoms so, initially, the individual won’t even know that this interaction is occurring. However, the individual may be placed at higher risk of experiencing a fracture that the medication might have prevented had it been taken correctly with a glass of water rather than with food or other beverage.
In addition to the negative effects of drug interactions, there may also be a beneficial effect, as seen with the prescription weight loss medicine orlistat (Xenical), which works on the basis of a drug-nutrient interaction. This particular medicine helps individuals lose weight through its ability to reduce the intestinal absorption of dietary fat, thus reducing the number of calories absorbed.
If a drug interaction negates or reduces the effectiveness of another medication, additional expenditures may result from added physician visits needed to modify the therapy. Adverse health outcomes such as hospitalization from serious drug interactions may also add considerable expense.
Clinical complications may also be caused by an interaction. For example, while adverse symptoms caused by a drug interaction may be serious, they may not initially be recognized as being caused by an interaction. This may result in additional interventions from healthcare professionals, including physician visits (possibly even specialists), hospitalization, and perhaps being prescribed additional medications that could cause further interactions.
Risk Factors for Drug Interactions
A number of risk factors that increase the likelihood of drug interactions have been identified, and many of these factors apply to older adults, putting them at a higher risk of experiencing one or more drug interactions, particularly as compared with the general population.
Number of Medications Consumed
The biggest factor influencing the likelihood of older adults experiencing a drug interaction is the number of medications they take since medication consumption increases with age. It makes sense that the more medicines an elder takes, the greater the risk that the medications will interact with each other. The chance of a drug interaction occurring when someone is taking only a few medications is small, but it is disproportionately larger if the number of medications taken is doubled. When an older adult takes more than 10 different medications, the individual is at least theoretically at risk for a minimum of one drug interaction.
Types of Medications Consumed
Certain medications such as blood thinners, those for high blood pressure, and psychoactive medications, including antidepressants or sleep medicines, are well known for their increased risk of interaction. Typically, medications from these classes are more commonly used by older adults, again putting this population at an increased risk of drug interactions. For example, older men are more likely to be taking prescription nitrate medications for the management of angina. If they also take an erectile dysfunction medication such a Viagra, Levitra, or Cialis, a severe lowering of their blood pressure could result.
Visiting More Than One Physician
Older adults often see one or more specialists in addition to their primary care physicians, and these specialists often prescribe medications. Because of this, an older adult may be taking 10 or more different medications prescribed by multiple physicians, most likely without extensive communication between prescribers.
Age-Related Changes in Physiology
As an individual ages, subtle changes in kidney and liver function and body makeup occur that may impact how a particular medication is metabolized and eliminated from the body, as well as how the medication is distributed throughout the different body tissues. These changes may contribute to drug interactions through various mechanisms.
Presence of Health Conditions
While many older adults remain healthy and vigorous well into their advanced years, the fact is that various health conditions, including high blood pressure, glaucoma, and lipid abnormalities, occur more frequently in older adults. The presence of these and other health conditions could predispose an older individual to various drug interactions due to the effect that such conditions can have on the body, as well as the likelihood that these conditions could be treated with additional medications.
Interactions With Herbal Medications
The increasing popularity of herbal or complementary medicines has raised the question of whether the multitude of available herbal products may interact with FDA-approved prescription and OTC medications.
Because these products are not prescription medications, they do not receive the regulatory scrutiny of the FDA that is required for prescription drug products. Consequently, there are no requirements for manufacturers of herbal products to research the possibility that their product(s) may interact with other medications or with nutrients.
Even though research studies on herbals are lacking, there is anecdotal information that certain herbal products can indeed interact with prescription and OTC medications and that these interactions can be significant. For example, it has been found that concurrent use of the blood thinner warfarin and the herbal product ginseng can result in significant increases in warfarin’s anticoagulant effect. Other herbals, including ginkgo, can increase the risk of bleeding and bruising in individuals taking warfarin.
Interactions Involving Alcohol
Alcohol can interact with a number of medications through various mechanisms. The most common concern arises when alcohol, itself a central nervous system depressant, is taken with other central nervous system depressants such as opioid pain medications (including morphine and related medications), sedatives, or tranquilizers. This combination of two or more central nervous system depressant medications can cause a variety of symptoms, ranging from drowsiness that could impair work function and driving ability to unconsciousness and possibly even coma or death, depending on the amount of alcohol and the number and type(s) of interacting medications.
Alcohol can also interact with medications via other mechanisms, including increasing stomach irritation when taken with medications that can cause this irritation, as with nonsteroidal anti-inflammatory medications such as ibuprofen.
When alcohol is ingested by an individual who is also taking certain oral antidiabetic medications, a potentially serious reduction in blood sugar occurs. Alcohol may also cause additional interactions based on other mechanisms.
Reducing the Chance of Drug Interaction
Admittedly, the topic of drug interactions is highly technical, but there are some steps and precautions that older adults can take to reduce the chance of such an interaction occurring.
Purchase All Prescription Medications From One Pharmacy
Prescription drugs are expensive, and older adults may be tempted to price shop and purchase each prescription from the pharmacy offering the lowest price. But this practice deprives elders of valuable pharmacy services that are designed to detect potential drug interactions and alert both the elder and the prescriber. Pharmacies use sophisticated software that can identify such interactions, but it works only if all of an individual’s prescriptions are in the database. It’s best if elders identify and use a pharmacy based on overall value, including price and other services such as patient counseling.
Older adults or caregivers should read and heed any auxiliary labels that may be affixed to prescription containers. If a prescription medication has a well-known interaction, a small auxiliary label will be affixed to the prescription container. When such a warning is given, elders should be sure to pay attention to it.
They should read any information such as handouts and leaflets that accompany their prescriptions. When they receive a new prescription or refill one, the pharmacy may provide them with a very detailed information sheet, including medications with which the prescription may interact. They should read this valuable information and compare it with other medications they may be taking.
Also, elders or caregivers should read the labels of nonprescription medications for drug interaction precautions. Just because a medication is available without a prescription doesn’t mean that it can’t be involved in a drug interaction. In fact, many OTC medications were formerly available only by prescription.
Older adults or caregivers with Internet access can go online and locate numerous drug interaction screening tools. These can be helpful for identifying potential interactions but they don’t give a definite answer since interactions may vary depending on a medication’s dosage, when the medications are taken with respect to each other, and patient variability.
It is important that older adults take a complete list of medications with them each time they visit their doctors, so they can consider possible interactions with any other prescriptions.
Also, it is important for elders to talk with the pharmacist about possible drug interactions, including nonprescription drugs. If using a mail order plan that doesn’t have access to a pharmacist, they may consider hiring the services of a senior care pharmacist. These professionals specialize in providing information rather than dispensing medications. They typically work in an office, though some make house calls so they can perform a detailed review of all medications to look for potential problems, including drug interactions. These professionals can be located through the Web site www.seniorcarepharmacist.com.
Be Proactive With Medications
Wise consumers must be aware that medications have the potential to interact with other medications, both prescription and OTC, as well as with nutrients and herbal products.
With a general understanding of drug interactions and their potential impact, older adults can play an important role in identifying and, ideally, preventing this potentially serious problem.
— William Simonson, PharmD, FASCP, CGP, is a certified geriatric pharmacist based in Suffolk, VA. His Web site is www.AskDrSi.com.