Copyright 2001
The Detroit News

One person's healthy eating can be another person's poison.

Take that lovely spinach salad you had for dinner. Though it's rich in iron and other nutrients, it would be dangerous for the millions of people who take anticoagulants (blood thinner medication). People on these kinds of medications need to avoid large servings of leafy green vegetables, because they can change the effect of the medication.

A warning also applies to people who take certain drugs for depression and eat cheese or sausage, and those who combine caffeine-rich coffee with the drug theophylline, an asthma medication.

Eating certain foods while taking medicine can change a drug's effectiveness, causing you to get more or less of the drug than prescribed. Some drugs can cause nutrient loss when taken over long periods of time. In some cases, these food-drug interactions can be harmful or even deadly.

"Most patients do receive the appropriate information about the drugs they're taking, and heed that advice about what foods to avoid," says Rozelle Dingle, a clinical pharmacist with the Nutrition Support Team with Henry Ford Hospital. "But some people are not aware that mixing certain foods with certain prescription drugs can cause serious interactions."

With prescription drug use continuing to rise, we all have cause for concern about our prescription medicines and how they may interact with food.

Last year, U.S. prescription drug sales grew 14.9 percent to $145 billion, according to the pharmaceutical tracking organization IMS America. Nearly two-thirds of that sales growth came from higher prescription volume as opposed to higher prices, according to the company.

"Approximately 85 million American adults take one or more prescription medicines," says Linda Golodner, president of the National Consumers League, an advocacy organization in Washington, D.C. "Yet, despite this widespread use, many consumers do not know about potential risks, side effects and possible drug interactions."

When you take a pill or swallow a liquid medication, a complex process begins.

Most medicines taken by mouth are not digested in the stomach. They travel into the small intestine, where they are broken down by enzymes. Then the drug is absorbed into the bloodstream through the walls of the small intestine and carried to your liver. There it is processed by enzymes and sent to the area of action, or where the drug's effect begins. Eventually, the remnants of the drug are eliminated through your urine or by breakdown in the liver.

But before this process can happen, the drug must be in your stomach with whatever else you're eating.

Sometimes the reaction between drugs and food is immediate. For example, taking the antibiotic tetracycline with food or milk quickly decreases the drug's effectiveness. That means you don't get as much drug as your doctor prescribed.

Other times, there is a buildup of the drug and chemicals found in food, and they react together and build to dangerous levels days or even weeks after you have started to combine them. Drugs called monoamine oxidase (MAO) inhibitors, often used to treat depression, can react with foods rich in the chemical tyramine. Tyramine is found in aged cheese, wine, beer and sauerkraut.

"If you eat those foods on a daily basis, tyramine can build up in your system," says Dingle. "You can have a high-blood pressure crisis that can lead to a stroke or a seizure."

Unfortunately, misinformation abounds. In the 1990s, doctors and pharmacists discovered grapefruit and grapefruit juice could influence how a drug works in the body. An erroneous press report said grapefruit juice reacted negatively with the popular prescription allergy antihistamines Claritin and Allegra and could cause serious heart problems. That report was repealed two days later.

However, grapefruit and grapefruit juice do interact with other medications. The scientists believe the contents of the juice or fruit inhibit enzymes in the small intestine that help to break down so many of the drugs we take. If those enzymes aren't available to break down the drug and render it inactive, that means more of the drug makes its way in to the bloodstream. Concentrations in the body are therefore higher.

"Doctors prescribe medications assuming this specific metabolic process is going to take place," says David Edwards, professor of pharmacy at Wayne State University's College of Pharmacy and Allied Health. "Taking grapefruit juice, for example, can circumvent this situation so that you get more drug absorbed than you usually would. So 10 mg of a medication could act more like 20 to 40 mg of the drug."

Many other foods fall into this class of causing interactions with medication. Eating onions or garlic while taking an anticoagulant, also called a blood thinner, can increase that drug's effect and lead to bleeding. And just as milk can decrease the effect of some antibiotics, eating highly acidic foods such as tomatoes or fruit juice causes a similar effect.

Some of the potential interactions are rather unremarkable. For example, the drug digitalis, prescribed to strengthen weak heart muscle contractions or correct irregular heartbeats, can be affected by high-fiber foods such as bran or prune juice. They cause the drug effect to be less than prescribed, meaning you don't get all of the medication your doctor wants you to have. Taking an antacid with your meal instead of one hour afterwards can decrease the effect of the medicine. Taking antibiotics such as tetracycline with dairy products can nullify the effect of the drug.

But other interactions can be severe -- even deadly.
* Combining the anti-asthma drug theophylline with caffeine can induce nausea, heart palpitations or seizures.
* The drug lithium, often used to normalize mood and behavior in bipolar disorder or treat alcohol addiction, is affected by salt. Too much salt, and the drug's effect is decreased. Too little, and the effect could increase.
* Following a high-protein diet can decrease the effect of levodopa, a drug used to treat Parkinson's disease. That means you may not see the desired effect for many weeks.
* Soybeans affect the cholesterol-lowering drug dextrothyroxine -- heavy consumption can interfere with thyroid function.
* Eating licorice while taking a diuretic (water pill) can cause excessive loss of the mineral potassium, which can lead to dangerous heart rhythms.
* When taken with tyramine-rich foods such as aged cheese or wine, the anti-cancer drug procarbazine can produce blood pressure high enough to kill.

The best advice to avoid these potentially dangerous situations is to become informed. Heed the warnings and dietary restrictions you receive from your doctor, nurse, pharmacist and dietitian, says Stephea Scheurer, a registered dietitian. She is the clinical nutrition and patient services manager at St. John Detroit Riverview hospital.

"In my experience, the patients are very receptive," says Scheurer, who counsels patients daily about their medications and diet. "People want to do whatever possible to maximize their health, and they all appreciate tips from a nutritional standpoint in order to do that."

Dietitians and pharmacists are specially trained in the reaction of drugs and food. Be sure to ask if you have any questions about what to eat or not eat while taking a medication.

Combinations to avoid
* Diuretic (water pill) + salt = body loses potassium and magnesium. Can lead to dangerous heart rhythms.
* Anticoagulants (blood thinners) + asparagus, spinach or other foods rich in vitamin K = more blood clotting, which can lead to heart attack or stroke.
* Anticoagulants (blood thinners) + onions/garlic = excess bleeding.
* Erythromycin or penicillin (antibiotics) + caffeine, tomatoes and/or fruit juices = increased acid production in stomach and decreased effectiveness of the drug.
* Monoamine oxidase inhibitors (antidepressant) + aged cheese, wine, sour cream = headaches, vomiting, potentially lethal increases in blood pressure.

Where to learn more
* www.drugfacts.com: Visitors can subscribe to newsletters, including a drug interaction newsletter. The site is meant for healthcare professionals, but much of the information is simple enough for the average reader.
* www.healthatoz.com: This site has a drug interaction database. Click on tools, then drug guide, and then drug interactions. Enter a drug name, and the site will bring up published interaction dangers.
* The National Consumers League offers a Food & Drug Interactions brochure. To receive a copy, send $2 for postage and handling to the National Consumers League, 1701 K St. NW, Suite 1200, Washington, DC 20006.

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