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Chapter 19 Food-Drug Interactions Key Terms Bioavailability: degree to which a drug or other substance reaches the circulation and becomes available to the target organ or tissue Drug-nutrient interactions: the results of the action between a drug and a nutrient that would not happen with the nutrient or drug alone © 2004, 2002 Elsevier Inc. All rights reserved. Key Terms—cont’d Half-life: amount of time it takes for the blood concentration of a drug to decrease by one half of its steady state level Side effect: adverse effect/reaction or any undesirable effect of a drug © 2004, 2002 Elsevier Inc. All rights reserved. Pharmacology Terms Stages of Drug Action Pharmacokinetics: movement of a drug through the body by absorption, distribution, metabolism, and excretion Pharmacodynamics: physiologic and biochemical effects of a drug or combination of drugs © 2004, 2002 Elsevier Inc. All rights reserved. Pharmacology Terms—cont’d Pharmacogenomics: genetically determined variations that are revealed solely by the effects of drugs © 2004, 2002 Elsevier Inc. All rights reserved. Therapeutic Importance Therapeutically important interactions are those that: —Alter the intended response to the medication —Cause drug toxicity —Alter normal nutritional status © 2004, 2002 Elsevier Inc. All rights reserved. Other Terms Bioavailability: % free to function Absorption rate: % absorbed and time for absorption Transported: amount in blood (free or bound) Metabolized: altered by enzymes in tissues Mixed-function oxidase system (MFOS): enzyme system that metabolizes drugs, carcinogens, compounds in foods, etc. © 2004, 2002 Elsevier Inc. All rights reserved. Patients at Risk for Food-Nutrient Interactions Patient with chronic disease Elderly Fetus Infant Pregnant woman Malnourished patient © 2004, 2002 Elsevier Inc. All rights reserved. Drug Effects on Nutrition Decreased or increased intake —Appetite —Taste —Nausea —Dry mouth Alter metabolism —Anti-vitamins —Monoamine oxidase inhibitors © 2004, 2002 Elsevier Inc. All rights reserved. Drug Effects on Nutrition—cont’d Change absorption —GI pH —Transit time or motility —Bile acid secretion or activity —Drug-nutrient complexes —Muscosal damage Change excretion © 2004, 2002 Elsevier Inc. All rights reserved. Nutrient Effects on Drugs Absorption —Note if drug is taken with or without food —Note which foods to avoid Metabolism —Changes in diet may alter drug action —Malnutrition alters albumin level (blood binding) and MFOS enzyme activity level © 2004, 2002 Elsevier Inc. All rights reserved. Nutrient Effects on Drugs—cont’d Excretion —Fluid status —Urinary pH © 2004, 2002 Elsevier Inc. All rights reserved. Important Interactions Oral contraceptives —Folate Antihypertensives —Ca —K —Mg MAOIs —Tyramine in foods © 2004, 2002 Elsevier Inc. All rights reserved. Key Information 1. Physician’s Desk Reference – food and drug interactions—there are other drug indexes 2. Generic or chemical name differs from brand name 3. Drugs are classified by action, manufacturer, class, brand name, and generic name 4. Over-the-counter drugs may be bought without prescription © 2004, 2002 Elsevier Inc. All rights reserved. Examples of Drug Categories That May Cause Loss of Appetite Antiinfectives Antineoplastics Bronchodilators Cardiovascular drugs Stimulants © 2004, 2002 Elsevier Inc. All rights reserved. Examples of Drug Classes That Cause Diarrhea Laxatives Antiretrovirals Antibiotics Antineoplastics © 2004, 2002 Elsevier Inc. All rights reserved. Drugs That May Increase Appetite Anticonvulsants Hormones Psychotropic drugs —Antipsychotics —Antidepressants, tricyclics, MAOIs © 2004, 2002 Elsevier Inc. All rights reserved. Drugs That May Affect Glucose Levels Antidiabetic drugs Drugs that can cause hypoglycemia Antiretrovirals, protease inhibitors Diuretics, antihypertensives Hormones © 2004, 2002 Elsevier Inc. All rights reserved. Medical Nutrition Therapy for Food-Drug Interactions Prospective: all MNT offered when the patient first starts a drug Retrospective: evaluation of symptoms to determine if medical problems might be the result of food-drug interactions © 2004, 2002 Elsevier Inc. All rights reserved. Enteral Nutrition and Drugs Drugs put in feeding tubes may cause: —Diarrhea —Drug-nutrient binding —Blocked tube Avoid adding drug to formula When drugs must be given through tube: —Stop feeding, flush tube, give drug, flush —Use liquid form of drug —Avoid crushing tablets © 2004, 2002 Elsevier Inc. All rights reserved. Summary All drugs are metabolized ahead of nutrients. Most drugs have nutritional status side effects. Always look for potential interactions. Watch for use of multiple drugs (polypharmacy) especially among the elderly! © 2004, 2002 Elsevier Inc. All rights reserved.