Listing the foods that make some drugs less effective
Examining interactions between drugs, vitamins, and minerals
Pinpointing drugs to be taken with/without food
Foods nourish your body. Medicines cure (or relieve) what ails you. The two should work together in perfect harmony. Sometimes they do, but sometimes they fight. In some cases, the medicine prevents your body from absorbing or using the nutrients in food, or the food (or nutrient) incapacitates the medicine.
The medical phrase for this is adverse interaction. This chapter describes several adverse interactions and lays out some simple strategies that enable you to short-circuit them.
Following Food and Drug Interactions
When you eat, food moves from your mouth to your stomach to your small intestine, where the nutrients that keep you strong and healthy are absorbed into your bloodstream and distributed throughout your body. Take medicine by mouth, and it follows pretty much the same path from mouth to stomach to the small intestine for absorption. Nothing is unusual about that.
A problem may arise when a food or drug brings the process to a halt by behaving in a way that interferes with your ability to digest, absorb, or use either the drug or the food (see Figure 25-1). For example:
Some drugs or foods change the natural acidity of your digestive tract so that you absorb nutrients less efficiently. For example, your body absorbs iron best when your stomach is acidic. Taking antacids reduces stomach acidity — and iron absorption.
Some drugs or foods change the rate at which food moves through your digestive tract, which means that you absorb more (or less) of a particular nutrient or drug. For example, eating prunes (a laxative food) or taking a laxative drug speeds things up so that medicines, like foods, move more quickly through your body, giving you less time to absorb either the medicine or the nutrients in the food.
Some drugs and nutrients bond (link up with each other) to form insoluble compounds that your body can’t break apart. As a result, you get less of the drug and less of the nutrient. The best-known example: Calcium (in dairy foods) bonds to the antibiotic tetracycline so that both move swiftly out of your body.
Some drugs and nutrients have similar chemical structures. Taking them at the same time fools your body into absorbing or using the nutrient rather than the drug. One good example is Coumadin (the generic version of Warfarin, a drug that keeps blood from clotting) and vitamin K (a nutrient that makes blood clot). Eating lots of vitamin K–rich leafy greens while taking Warfarin counteracts the medicine’s ability to prevent blood clots.
Some foods contain chemicals that either lessen or intensify the natural side effects of certain drugs. For example, the caffeine in coffee, tea, and cola drinks reduces the sedative effects of antihistamines and some antidepressant drugs but increases the nervousness, insomnia, and shakiness common with pills such as cold medications containing caffeine or a decongestant (an ingredient that temporarily clears a stuffy nose).
FIGURE 25-1: Some foods may affect the way your body interacts with drugs.
Listing the Reactions of Drugs and Certain Foods
Sometimes the combinations of interacting foods and drugs are surprising. Astounding. Or breathtaking.
Everyone knows that people with asthma may find it hard to take a deep breath around the barbecue. The culprit’s the smoke, right? Yes. And no. Breathing in smoke does irritate air passages, but — the surprise — eating charcoal-broiled food speeds the body’s elimination of theophylline, a widely used asthma drug, reducing the drug’s ability to protect against wheezing. Take the drug, eat the food, and maybe end up wheezing.
Another potential troublemaker is an acidic beverage, such as fruit juice or soft drinks, which may inactivate the antibiotics erythromycin, ampicillin, and penicillin.
Grapefruit juice is a particularly potent offender.
In the mid-1990s, researchers tracking the effects of alcohol beverages on the blood pressure drug felodipine (Plendil) tripped across the Grapefruit Effect, a dramatic reduction in the ability to metabolize and eliminate certain drugs. Why? Because grapefruit juice contains substances that suppress the effectiveness of CYP 3A4, an intestinal enzyme required to convert many drugs to water-soluble substances you can flush out of your body; without the enzyme activity, you can’t get rid of the drug. The result may be an equally dramatic rise in the amount of medication in your body, leading to unpleasant side effects. Table 25-1 lists the medicines known to be affected by grapefruit juice.
MedicineNet.com; Rolfes, Sharon Rady, Kathryn Pinna, and Elie Whitney, Understanding Normal and Clinical Nutrition, Seventh Edition (Belmont, CA: Thomason Higher Education, 2006)
Caveat #1: Taking a slow-release medicine along with grapefruit juice may cause the entire dose of medicine in the pill or capsule to be released and metabolized at once. Caveat #2:Table 25-1 is not a complete list of medicines subject to the grapefruit effect. Check with your doctor or pharmacist whenever a new medicine is prescribed.
Discovering Drug Interactions with Nutrients
Like food, individual nutrients — vitamins and minerals — may also interact with medicines. Here are four examples:
Antacids containing aluminum compounds bind with the bone-building mineral phosphorous, carrying it right out of your body.
Antiulcer drugs cimetidine (Tagamet) and ranitidine (Zantac) can make you positively giddy. These drugs reduce stomach acidity, which means the body absorbs alcohol more efficiently. According to experts at the Mayo Clinic, taking ulcer medication with alcohol leads to twice the wallop. Drink one beer, and you feel as though you’ve had two.
Diuretics, commonly known as water pills, increase urination, which increases your loss of the mineral potassium. To make up what you lose, experts suggest adding potassium-rich bananas, oranges, spinach, corn, and tomatoes to your diet.
Oral contraceptives reduce the body’s absorption of the B vitamin folate and possibly B12.
Table 25-2 lists some common vitamin/mineral and drug interactions. (For more information on supplements, see Chapter 13.)
James J. Rybacki, The Essential Guide to Prescription Drugs 2002 (New York: Harper Collins, 2001); Brian L. G. Morgan, The Food and Drug Interaction Guide (New York: Simon and Schuster, 1986); Eleanor Noss Whitney, Corinne Balog Cataldo, and Sharon Rady Rolfes, Understanding Normal and Clinical Nutrition, 4th ed. (Minneapolis/St. Paul: West Publishing, 1994)
Using Food to Improve a Drug’s Performance
Not every food and drug interaction is an adverse one. Sometimes a drug works better or is less likely to cause side effects when you take it on a full stomach. For example, aspirin is less likely to upset your stomach if you take the painkiller with food, and eating stimulates the release of stomach juices that improve your ability to absorb griseofulvin, an antifungus drug.
Table 25-3 lists some drugs that may work better when your stomach is full.
Table 25-3 Drugs That Work Better on a Full Stomach
Purpose
Drug
Analgesics (painkillers)
Acetaminophen
Aspirin
Codeine
Ibuprofen
Indomethacin
Mefenamic acid
Metronidazole
Naproxen/naproxen sodium
Antibiotics, antivirals, antifungals
Ethambutol
Griseofulvin
Isoniazid
Ketoconazole
Pyrimethamine
Antidiabetic agents
Glipizide
Glyburide
Tolazamide
Tolbutamide
Cholesterol-lowering agents
Cholestyramine
Colestipol
Lovastatin
Probucol
Gastric medications
Cimetidine
Ranitidine
James J. Rybacki, The Essential Guide to Prescription Drugs 2002 (New York: Harper Collins, 2001)
A problem may arise when a food or drug brings the process to a halt by behaving in a way that interferes with your ability to digest, absorb, or use either the drug or the food (see Figure 25-1). For example:
Everyone knows that people with asthma may find it hard to take a deep breath around the barbecue. The culprit’s the smoke, right? Yes. And no. Breathing in smoke does irritate air passages, but — the surprise — eating charcoal-broiled food speeds the body’s elimination of theophylline, a widely used asthma drug, reducing the drug’s ability to protect against wheezing. Take the drug, eat the food, and maybe end up wheezing.