Nutrition For Dummies
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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. This table lists the medicines known to be affected by grapefruit juice.

Grapefruit Juice versus Meds
Condition Drug Class Drug (Brand Name)
Allergy Antihistamine fexofenadine (Allegra)
Cough Cough suppressant dextromethorphan (DXM)
Depression Antidepressant fluvoxamine (Luvox, Faverin)
Diabetes, Type 2 Meglitinide (lowers blood sugar) repaglinide (Prandin)
Erectile dysfunction Enzyme inhibitor (increases blood flow) sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra)
High cholesterol Statins atorvastatin (Lipitor), lovastatin (Mevacor), simvastatin Zocor. Note: Pravastatin (Pravachol) is not affected.
HIV Antiretoviral ritonavir (Novir), saquinavir (Invirase, Fortovase)
Hypertension Calcium channel blocker felodipine (Nitrendipine, Plendil), losartan (Cozaar), nicardipine (Cardene), nimodipine (Nimotop), nisoldipine (Sular), verapamil (Verelan)
Insomnia Sleep aid zolpidem (Ambien)
Irregular heartbeat Antiarrhythmic amiodarone (Cordarone), carvedilol/verapamil (Calan SR, Covera HS, Isoptin SR, Verelan), dronedarone (Multaq), disopyramide (Norpace), quinidine (Quinidex, Cardioquin, Quinora)
Migraine Ergot alkaloid ergotamine, ergotamine & caffeine (Cafergot, Ergomar), OCD
Pain Narcotics codeine, methadone, morphine, oxycodone
Psychosis Anti-psychotic quetiapine (Seroquel)
Seizures Anti-seizure carbamazepine (Tegretol)
Transplants, severe Immunosuppressant cyclosporine (Neoral, Sandimmune), tacrolimus (Prograf)
Source:; 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: The table is not a complete list of medicines subject to the grapefruit effect. Check with your doctor or pharmacist whenever a new medicine is prescribed.

About This Article

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Carol Ann Rinzler is a former nutrition columnist for the New York Daily News and the author of more than 30 health-related books, including Controlling Cholesterol For Dummies, Heartburn and Reflux For Dummies, The New Complete Book of Food, the award-winning Estrogen and Breast Cancer: A Warning for Women, and Leonardo’s Foot, which the American Association for the Advancement of Science described as “some of the best writing about science for the non-scientist encountered in recent years.”

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