Paging Dr. Frischer: Food and medication

What we eat and when we do it is significant for so very many reasons. Among the most important relates to our medications. You have likely heard warnings such as “Never drink grapefruit juice with cholesterol medication.”
Medication effectiveness is an especially important issue for older adults; while they make up roughly 13% of the population, they account for 34% of prescriptions and 30% of over-the-counter drugs taken in the United States. About two of every five people on Medicare report taking five or more prescription medications. Older patients often have more than one doctor prescribing for them, making it difficult to track all of the medications. Drugs might interact with each other, or with another disease process. To further complicate matters, as we age, physiological changes affect how a drug is absorbed, distributed, metabolized, and excreted.
On top of all of these factors, the way in which we consume our food and drink can significantly impact a medicine’s safety and effectiveness. Let’s take a look at some of the most common food/drug interactions.
Grapefruit is well known for interacting with a variety of different drugs, resulting in either a higher or lower concentration of the medication in the blood. This can lead to an increased risk of serious side effects. Grapefruit contains furanocoumarins, which can change the way that the body metabolizes a drug by inhibiting an enzyme. Grapefruit also contains bioflavonoids (as do Seville oranges, pummelos, rose hips and black currants). Bioflavonoids affect most calcium channel blockers (prescribed for high blood pressure), statins (cholesterol-lowering drugs), antihistamines, some antibiotics (including ciprofloxacin), thyroid medication, birth control pills, stomach acid drugs, and some cough suppressants. If you use any of these medicines, it is best to simply avoid grapefruit altogether.
Green leafy vegetables such as kale, collards, spinach, turnip greens, Brussels sprouts, broccoli, asparagus, and endive are high in vitamin K, which diminishes the effectiveness of Coumadin (warfarin), a commonly used blood thinner. Coumadin treats and prevents blood clots, and prevents strokes in patients with atrial fibrillation. Other foods that can affect Coumadin levels include cooked onions and soy. The trick is actually not to avoid greens, but rather to eat a consistent amount, so that Coumadin levels in the blood remains steady.
I am a fan of black licorice. In sufficient quantities, glycyrrhiza, contained in licorice root, can lead to low potassium, salt and water retention, edema, and high blood pressure. Glycyrrhiza can decrease the effectiveness of blood pressure medicines and the blood thinner Coumadin. By the way, did you know that most licorice root production is used for tobacco products?
Dairy products can decrease the effectiveness of some antibiotics, including tetracycline, ciprofloxacin, and azithromycin. The calcium and magnesium in dairy can bind to the antibiotics and prevent their absorption. (However, note that certain antibiotics, like metronidazole (Flagyl) should be taken with milk or water in order to prevent stomach upset.) Dairy can also decrease iron absorption.
Salt substitutes typically replace sodium with potassium. This can decrease the effectiveness of Lanoxin (digoxin), used to treat congestive heart failure; and ACE inhibitors, used to treat high blood pressure. Those with decreased kidney function already have a hard time eliminating potassium, and should avoid salt substitutes.
When is it important to have a full or an empty stomach? NSAID’s like Motrin, Advil, and Aleve should be taken with food because they can be irritating to the stomach lining. Tylenol is best taken on an empty stomach because food may slow its absorption. Antihistamines like Claritin, Zyrtec, and Allegra are also best taken on an empty stomach – they will be more effective. Certain antibiotics (including azithromycin and tetracycline) have poor absorption when taken with food.
Alcohol can be dangerous when combined with anti-anxiety medication like Xanax, Ativan, and Klonopin; antidepressants; or sleep medication, because it may add to the sedating effects of these drugs. Alcoholic can also increase or prolong the effects of insulin and oral diabetic medications, leading to low blood sugar. Alcohol and Tylenol are a bad combination; two or more drinks per day can increase liver toxicity.
Understanding of drug/drug, food/drug, and herb/drug interactions is rapidly growing. Further, genetic factors affecting pharmacokinetics and pharmacodynamics are being studied, which is expected to lead to improved drug safety and to enable individualized drug therapy. It’s extremely complex! I urge you to pay close attention to recommendations from your physician and your pharmacist.

Dr. Alan Frischer is former chief of staff and former chief of medicine at Downey Regional Medical Center. Write to him in care of this newspaper at 8301 E. Florence Ave., Suite 100, Downey, CA 90240.