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Drug Interaction 'Pearls': Asking the Right Questions
by Diane B. Crutchfield, D.Ph., C.G.P.
Geriatric Times January/February 2001 Vol. II Issue 1
(This article is the first in a two-part series. Part II is scheduled to appear in the March/April issue-Ed.)Of the thousands of known potential drug interactions, how many are significant? Which patients will suffer an adverse outcome? Which outside factors that may impact drug interactions, such as lifestyle, are unknown to the health care professional?
Numerous articles have been written on the topic of adverse drug reactions (ADRs), many of them in previous issues of Geriatric Times. Drug interactions are typically considered one type of ADR, also known as therapeutic misadventures or drug-related problems. This article is the first of two that will provide "pearls" regarding drug-food interactions, drug-lifestyle interactions and drug-drug interactions.
The elderly make up 12.7% of the U.S. population but consume approximately 34% of total prescription medications and up to 30% of nonprescription medications. It is well known that the elderly population is at greater risk of negative outcomes from drug interactions due to polypharmacy and the physiological changes of aging. On average, individuals 65 to 69 years old take nearly 14 prescriptions per year, and individuals aged 80 to 84 take an average of 18 prescriptions per year (American Society of Consultant Pharmacists, 2000).
A complete review of drug interactions is beyond the scope of this article, but by sharing cases found in my own consulting practice, I hope to provide the reader with useful drug interaction information. My intent is twofold. First, I want to increase awareness among health care providers of the importance of information gathering from the geriatric patient and/or caregiver and sharing that information with other health care providers. Second, I want to emphasize the significance of recognizing drug interactions based on pharmacological activity and other factors that are dependent on the individual patient and cannot be ascertained by use of drug interaction software alone.
Mrs. M, a 72-year-old female, was sent to the hospital with exacerbation of chronic obstructive pulmonary disease (COPD). Her theophylline dose was continued at 400 mg tid, as given in the nursing home where her level was within normal limits. A few days after hospital admission, she had severe vomiting and increased agitation. Her serum theophylline level was 24 mcg/ml.
Pearl No.1
Remember to inquire about lifestyle, such as smoking. In this case, smoking significantly inhibits the metabolism of the-ophylline. Although most nursing homes provide a smoking area for patients, hospitals typically do not. The theophylline dose was adjusted based on this patient's heavy tobacco use, and when it was suddenly stopped, her levels became toxic.
In an outpatient anticoagulant clinic, a change of seasons can have an impact on patients' International Normalized Ratio (INR) values. When patients consume more green, leafy vegetables, which are abundant in the summer months, the warfarin (Coumedin) may have to be adjusted due to the anticoagulant effect of vitamin K found in these and other foods.
Pearl No.2
Ask about diet, specific types of food and quantity. I have found that dietary managers in some institutional settings may not be aware of this drug-food interaction or may not be aware that the patient is taking warfarin, for example. An effort to provide the patient with requested foods also complicates the situation.
Diet is also significant for those patients on monoamine oxidase inhibitors. Outpatients should be provided with a list of foods with high tyramine content to prevent a potential hypertensive crisis. In the nursing home, pharmacy and nursing should ensure that the dietary department is aware of dietary restrictions based on medication use.
A resident of an assisted-living facility once asked for a review of her medications. She named only three prescription drugs, including ranitidine (Zantac), digoxin (Lanoxin) and zolpidem (Ambien). At final count, however, she was routinely taking 10 medications; there were several potential drug interactions.
Pearl No.3
Possible questions about interactions for this patient are indicated below. An alternative to asking the patient for a list of over-the-counter medications is to be specific.
- What do you take when you have a headache or other pain? Do you take it every day? One or more times/week? (Ibuprofen increases risk of dyspepsia.)
- What medicine do you buy at the drug store or grocery store without a prescription when you need a laxative? Do you need to take it every day? (Bulk-forming laxatives decrease absorption of digoxin.)
- What kind of vitamins do you take every day? (Multiple vitamin with iron can pose a risk.)
- Do you take any herbal or natural supplements? (St. John's wort can pose problems.)
- Do you take anything to help you sleep? (Tylenol PM contains diphenhydramine, additive with Ambien.)
- What do you take for cough/cold/sinus symptoms? (Tylenol Sinus Nighttime also contains diphenhydramine.)
- What do you take for indigestion? (Antacids may interfere with absorption of ranitidine and digoxin but with minimal effect.)
How much alcohol is the patient consuming? This is an important lifestyle factor to consider when encouraging the use of acetaminophen. Warnings on the product labeling indicate patients should notify their physician if they consume more than three to four alcoholic drinks per day, due to the potential for hepatic toxicity. Ask patients about alcohol use without patronizing them.
Medication compliance is an issue for anyone taking medications, but it is a particular concern for elderly patients whose quality of life may be dependent on appropriate and necessary medications. Too often we fail to recognize the potential for a drug interaction or toxicity resulting from placement in an institutional setting. Mr. M, an 83-year-old male, was admitted to the nursing facility with an extensive list of medications, including digoxin 0.25 mg daily; warfarin 2 mg daily; propanolol (Inderal) 20 mg three times daily; albuterol (Proventil) inhaler two puffs, four times daily; and St. John's wort daily, among others. After less than one week, he became anorexic, nauseated and complained of nervousness.
Pearl No.4
Although a fairly accurate list of the resident's current medications was provided by the spouse, no one asked if the patient was taking all of the medications as ordered when he was at home. To add to the problem, the pharmacy did not stock St. John's wort, and the patient did not receive any for about a week. Drug interactions with herbal supplements are not well defined, but some sources indicate that digoxin levels may be reduced by St. John's wort. As a result of not taking the supplement at the facility and receiving the medication daily from the nursing staff, the patient was digoxin toxic. We did not know that the albuterol inhaler was being used only as needed at home, and the routine use of the b-agonist around the clock likely contributed to his nervousness. This could have been even more prominent if he had not also been taking propanolol, a b-blocker. The b-blocker would also reduce the clinical effects of the inhaler, while still allowing side effects to be observed.
Hopefully, compliance is improved for the institutionalized elderly, but it cannot be assumed. Ask if the patient has been taking the prescribed medications as ordered.
As stated earlier, the intent of this article is to increase awareness about drug interactions and the importance of interdisciplinary communication among health care providers and with the patient in order to get answers to key questions. In the next column, I will look more specifically at drug-drug interactions and how to avoid, or at least minimize, them in the elderly population.
Dr. Crutchfield is president of Pharmacy Consulting Care, an independent consultant pharmacy practice located in Knoxville, Tenn.
References
American Society of Consultant Pharmacists (2000), Senior care pharmacy facts. Alexandria, Va: American Society of Consultant Pharmacists.
