Drug-food interaction

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In providing drug information to patients, it is important to provide information on when to take their medications in relation to food intake. Consequences of drug-food interactions may include delayed, decreased, or enhanced absorption of the drug. Food may also affect the bioavailability, metabolism, and excretion of certain medications. 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.

Sources: 1. http://www.uspharmacist.com/oldformat.asp?url=newlook/files/feat/acf2f08.htm 2. http://www.globalrph.com/drugfoodrxn.htm 3. Lewis CW, Frongillo EA, Roe DA. Drug-nutrient interactions in three long-term care facilities. J Am Diet Assoc. 1995;95:309-315. 4. Drew RH, Gallis HA. Azithromycin-spectrum of activity, pharmacokinetics, and clinical applications. Pharmacotherapy. 1992;12:161-73. 5. Zithromax (azithromycin) product information. Pfizer Laboratories, New York, NY: April, 1995. 6. Jonkman JH. Food interactions with sustained-release theophylline preparations. A review. Clin Pharmacokinet. 1989;16:162-79. 7. Fosamax (alendronate sodium) product information. Merck & Co., West Point, PA: 1995. 8. Polk RE, Healy DP, Sahai J, Drwal L, Racht E. Effect of ferrous sulfate and multivitamins with zinc on absorption of ciprofloxacin in normal volunteers. Antimicrob Agents Chemother. 1989;33:1841-4. 9. Rodin SM, Johnson BF. Pharmacokinetic interactions with digoxin. Clin Pharmacokinet. 1988;15:227-44.