Drug-food interaction

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A drug-food interaction is an adverse drug event that may include delayed, decreased, or enhanced absorption of the drug. Food may also affect the bioavailability, metabolism, and excretion of certain medications. Drugs may also have adverse effects on food and nutrition.


The patient may experience an adverse drug side effects or drug toxicity, or may not receive the full therapeutic benefit of the medication.

Elderly patients may be at a greater risk for drug-food interactions because they typically consume more medications for their chronic medical conditions. A study of drug-nutrient interactions in long-term care facilities found a significant relationship between the number of medications a resident consumed and the number of drug-nutrient interactions for which a resident was at risk.3

Food may affect drug absorption in the GI tract by altering gastric pH, secretion, gastrointestinal motility, and transit time. This may result in a change in the rate of absorption or extent of drug absorption, or both. For example, azithromycin absorption is decreased when it is taken with food, resulting in a 43% reduction in bioavailability.4,5

Sustained-release theophylline products such as Theo-24 and Uniphyl when taken with high-fat foods may cause a sudden release (dose dumping) of theophylline, resulting in increased theophylline concentrations and possible toxicity. Children are more prone to this interaction than adults.6 Ingestion of food or beverages other than plain tap water significantly affects the absorption of alendronate sodium (Fosamax), a bisphosphonate indicated for the treatment of osteoporosis and Paget’s disease and now also for prevention of osteoporosis and osteoporotic fractures in postmenopausal women. The oral bioavailability of the 10 mg tablet is 0.59% for men and 0.78% for women when taken after an overnight fast and 2 hours before breakfast. Bioavailability is significantly reduced (>85%) when alendronate sodium is taken either concurrently with or 2 hours after breakfast. The bioavailability is reduced by 60% when the drug dose is taken with black coffee or orange juice.7

Components of food may directly interact with certain medications, forming complexes or chelates. These inactive structures are poorly absorbed from the gastrointestinal tract. For example, tetracycline forms chelates with the calcium in milk, dairy products, and antacids. Complexation reactions occur when iron binds with ciprofloxacin. The bioavailability of ciprofloxacin is reduced by 52% in the presence of iron.8

Patients taking digoxin should avoid taking bran fiber, pectin-containing foods such as apples or pears, or fiber-containing, bulk-forming laxatives at the same time, since these agents may bind to the digoxin, decreasing its absorption. This interaction could result in decreased serum concentrations of digoxin and therapeutic effectiveness.9

It is advisable to take some medications with food to reduce gastrointestinal irritation and possible nausea. Examples of these medications include potassium supplements, ferrous sulfate, nonsteroidal anti-inflammatory drugs, estrogen, prednisone, tacrine, terfenadine and nitrofurantoin.

Of the cholesterol-lowering agents, lovastatin (Mevacor) should be taken with food to enhance gastrointestinal absorption and bioavailability. Simvastatin (Zocor), pravastatin (Pravachol), and fluvastatin (Lescol) may be taken without regard to food.

Adverse Effects of Drugs on Food and Nutrition: (10, 11, 12)

While it is appreciated that foods and nutrients can interfere with drugs, it is less appreciated that drugs can compromise nutrition by interfering with nutrient intake, absorption, storage, excretion or metabolism in the body. With the notable exceptions of antibiotics and chemotherapy, these negative effects are most common and significant with chronic medications and polypharmacy. Malnutrition increases hospital length of stay and impairs immunity, wound healing, and recovery. There is an unaddressed need for informatics applications within computerized order entry systems which address clinically significant food-drug and drug-food interactions.

1. Drugs can alter food intake and nutrition status:

• Appetite increased or decreased, unusual food cravings

• Metabolic rate increased or decreased

• Taste/smell altered

• Oral side effects e.g. dry mouth/mouth pain

• Difficulty swallowing

• Nausea/Vomiting/Diarrhea: decreases intake, increases losses

• Drugs may increase mineral intake due to ingredients (e.g. large amounts of sodium in some antacids, this is declared on over-the-counter medications but not on prescription drugs).

• Polypharmacy is associated with malnutrition

2. Drugs can change nutrient absorption:

• Drugs may speed up gut transit; this reduces nutrient absorption from food.

• Drugs may slow down gut transit, this increases nutrient absorption and/or cause constipation, increasing the need for fiber and fluids.

• Drugs can increase the pH in the stomach (e.g. H2 receptor blockers and proton pump inhibitors) which will decrease the bioavailability of several nutrients (e.g. iron and vitamin B12) as well as alter the normal gut flora (also known as the microbiota).

• Drugs (e.g. antibiotics) can decrease and alter normal gut flora balance necessary for the absorption of vitamin K and B vitamins (B1, B2, B6, B12, and biotin) and the synthesis and absorption of short chain fatty acids. The alteration of vitamin K nutrition may in turn alter drug effect of warfarin, increasing risk of unwanted bleeding.

• Drugs can bind to nutrients (e.g. bile acid sequestrants impair absorption of fat soluble vitamins and fat soluble phytochemicals).

• Drugs can impair absorption (e.g. folic acid supplementation may be indicated if taking: metformin, triamterene, antacids, methotrexate, birth control pills, anti-inflammatory pain medicines, and anti-convulsants. However avoid excess folic acid if on anti-seizure medications, as it may trigger a seizure.)

3. Drugs can change nutrient excretion:

• Increase urinary excretion (e.g. Lasix increases losses of sodium, potassium, chloride, and magnesium, thiamin)

• Decrease urinary excretion (e.g. potassium sparing diuretics like spironolactone)

4. Drugs can change nutrient metabolism, for example:

• Isoniazid, used for tuberculosis treatment, causes vitamin B6 deficiency by impairing the metabolic activation of vitamin B6 to its active co-enzyme form.

• Anticonvulsants (e.g. phenytoin and phenobarbital) impair the 25-hydroxylation of vitamin D in the liver, leading to vitamin D deficiency and risk of rickets in children and osteomalacia/osteoporosis in adults. Anticonvulsants also increases need for vitamin K which also plays a role in bone health.

Submitted by Sara Lee Thomas


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  2. http://www.globalrph.com/drugfoodrxn.htm
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  7. Fosamax (alendronate sodium) product information. Merck & Co., West Point, PA: 1995.
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