Dangerous Food-Drug Interactions
Consider these surprising facts: Older adults comprise 13% of the population but account for 34% of all prescriptions and 30% of all over-the-counter drugs used in the United States. In addition, a survey of 17,000 Medicare beneficiaries conducted in 2007 found that two of every five patients reported taking five or more prescription medications. This same survey also revealed that older patients often have more than one prescribing physician, making it difficult to track the total number and types of medications elders take. At the same time, physiological changes related to aging affect the absorption, distribution, metabolism, and excretion of drugs, as well as food.
What these facts add up to, says Joel Zive, PharmD, vice president of Zive Pharmacy & Surgical, Inc in Bronx, NY, and a spokesman for the American Pharmacists Association, “is a greater risk of food-drug interactions in older Americans.”
Below are the ill-advised combinations that Zive believes comprise the top 10 types of drug-nutrient interactions affecting older adults, along with his recommendations for preventing potentially deadly problems.
1. Warfarin and Vitamin K
“It’s not that patients should avoid foods that contain vitamin K,” advises Zive. “Rather, they should keep their intake consistent from day to day.”
He describes a scenario that could spell trouble for an older adult: “If a doctor tells a patient that they should lose weight and they, in turn, start to eat more greens, their vitamin K intake will go up, and this will counteract the anticlotting action of warfarin.”
2. Insulin, Oral Diabetic Agents, and Alcohol
With a doctor’s approval, and in the absence of other health conditions such as pancreatitis, elevated triglycerides, and neuropathy, older adults with diabetes may be able to enjoy up to two drinks per day. A drink is defined by the American Diabetes Association as a 12-ounce beer, a 5-ounce glass of wine, or 1.5 ounces of a distilled beverage such as whiskey, vodka, or gin. Individuals can reduce the risk of low blood sugar by having alcoholic drinks at mealtime or by having a snack along with the drink.
In addition, certain oral diabetic medications such as chlorpropamide (Diabinese) can cause dizziness, flushing, and nausea when taken along with alcohol.
3. Digoxin, High-Fiber Diets, and Herbs
Dietary fiber, specifically insoluble fiber such as wheat bran, can slow down the absorption of digoxin and lessen its effectiveness. To prevent this, elders should take digoxin at least one hour before or two hours after eating a meal.
Herb use can also affect digoxin. For example, ginseng can elevate blood levels of digoxin by as much as 75%, while St. John’s Wort decreases blood levels of this drug by 25%.
“It’s important for the patient to recognize signs of digoxin toxicity,” says Zive. “These include a yellow tint to vision and the appearance of halos around objects, as well as weakness, confusion, dizziness, and nausea and vomiting.”
4. Statins and Grapefruit
Side effects of statins include muscle soreness and liver abnormalities reflected in high transaminase levels (serum glutamic-oxaloacetic transaminase and serum glutamic pyruvic transaminase) on a blood test.
This interaction is especially strong with simvastatin (Zocor) and lovastatin (Altoprev), milder with atorvastatin (Lipitor), and nonexistent for pravastatin (Pravachol), so it’s important for elders to check whether their prescribed statin drugs do interact before giving up vitamin C-rich grapefruit.
5. Calcium Channel Blockers and Grapefruit
It doesn’t take a jumbo serving of grapefruit to produce a deleterious effect either. For example, a single 6-ounce glass of juice can reduce levels of CYP3A4 by nearly 50%. This effect dissipates slowly. One study indicated that one third of the impact on CYP3A4 from grapefruit juice was still evident a full 24 hours later.
The interaction between grapefruit and calcium channel blockers is strongest, for example, with felodipine (Plendil), nicardipine (Cardene), and nisoldipine (Sular) and weaker with amlodipine (Norvasc), diltiazem (Cardizem), and nifedipine (Adalat).
Tangelos, a cross between a tangerine and grapefruitlike pomelo and Seville oranges, a bitter citrus fruit used to make marmalades, can have the same deleterious effects as grapefruit on both statins and calcium channel blockers.
6. Erectile Dysfunction Drugs and Grapefruit
7. Acetaminophen and Alcohol
This interaction can be especially problematic in older adults, says Zive, since the liver’s ability to diminish drugs decreases with age. “The liver of a 65 year old doesn’t function the same way it did at age 25,” he says.
8. Antibiotics and Dairy Products
To avoid problems, Zive recommends taking an antibiotic one hour before or two hours after a meal.
However, there’s no need to avoid milk and dairy with all antibiotics. For example, it’s recommended that metronidazole (Flagyl) should be taken with water or milk to prevent stomach upset.
9. MAOIs and Tyramine-Containing Foods
“Foods containing tyramines, such as some red wines, malt beer, smoked fish, aged cheeses, and dried fruits, can cause a hypertensive crisis or severe and dangerous elevation in blood pressure when taken with this class of antidepressants,” says Zive.
10. Antithyroid Drugs and Iodine-Rich Foods
Antithyroid drugs work by preventing iodine absorption in the stomach. A high-iodine diet requires higher doses of antithyroid drugs. The higher the dose of antithyroid drugs, the greater the incidence of side effects that include rashes, hives, and liver disease.
The richest dietary sources of iodine are seafood and seaweed, such as kelp and nori. Iodine is also found in iodized salt and to a lesser extent in eggs, meat, and dairy products.
— Carol M. Bareuther, RD, is a St. Thomas, U.S. Virgin Islands-based writer who contributes to a variety of regional, national, and international publications.