Article Archive

Fall 2008

Dangerous Food-Drug Interactions
By Carol M. Bareuther, RD
Aging Well
Vol. 1 No. 4

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
Warfarin (Coumadin) is a blood-thinning medication that helps treat and prevent blood clots. Eating certain foods, especially those rich in vitamin K, can diminish warfarin’s effectiveness. The highest concentrations of vitamin K are found in green leafy vegetables such as kale, collards, spinach, turnip greens, Brussels sprouts, broccoli, scallions, asparagus, and endive.

“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
An alcoholic drink can increase or prolong the effects of insulin or oral diabetic agents (pills) and thus lead to hypoglycemia or low blood sugar. The glucose-lowering action of alcohol can last as long as eight to 12 hours. Symptoms of hypoglycemia include nervousness, sweating, trembling, intense hunger, weakness, palpitations, confusion, drowsiness, and ultimately coma.

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
Digoxin (Digitalis, Digitek, Lanoxin) is used to strengthen the contraction of the heart muscle, slow the heart rate, and promote the elimination of fluid from body tissues.

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
Statins are highly effective cholesterol-lowering drugs. Unfortunately, says Zive, “Drinking grapefruit juice or eating fresh grapefruit can increase the amount of some statins in your blood and lead to potentially greater side effects of these drugs.”

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
Calcium channel blockers are prescribed for high blood pressure. A natural element found in grapefruit latches onto the intestinal enzyme called CYP3A4, which alters the breakdown of the calcium channel blockers, possibly resulting in excessively high blood levels of the drug, along with an increased risk of serious side effects.

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
Although unproven, evidence points to the likely fact that grapefruit juice gives a boost to blood levels of erectile dysfunction drugs such as sildenafil (Viagra). This may seem like a boon to some men, but it could trigger headaches symptomatic of fatal or near fatal conditions, flushing, or low blood pressure.

7. Acetaminophen and Alcohol
The over-the-counter pain reliever acetaminophen (Tylenol) and alcohol don’t mix.
“Two or more alcoholic drinks per day can increase the liver toxicity of Tylenol,” says Zive. “This toxicity can happen even if a patient takes less than the maximum 4 grams, or eight tablets, of Tylenol per day.”

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
Dairy products such as milk, yogurt, and cheese can delay or prevent the absorption of antibiotics such as tetracyclines and ciprofloxacin (Cipro). This occurs because the calcium in such foods binds to the antibiotics in the stomach and upper small intestine to form an insoluble compound.

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
Monoamine oxidase inhibitors are an older type of antidepressant still prescribed, albeit less frequently, due to their serious side effects.

“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 are compounds that interfere with the body’s production of thyroid hormones, thereby reducing the symptoms of hyperthyroidism. According to a broad body of research, Americans’ high-iodine diets account for the lower remission rate of hyperthyroidism in those who are prescribed antithyroid drugs.

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.