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Nutrition can affect the body's response to drugs; conversely, drugs can affect the body's nutrition.

Foods can enhance, delay, or decrease drug absorption. Foods impair absorption of many antibiotics. They can alter metabolism of drugs; eg, high-protein diets can accelerate metabolism of certain drugs by stimulating cytochrome P-450. Eating grapefruit can inhibit cytochrome P-450 34A, slowing metabolism of some drugs (eg, amiodarone Some Trade Names
CORDARONE
Click for Drug Monograph
, carbamazepine Some Trade Names
TEGRETOL
Click for Drug Monograph
, cyclosporine Some Trade Names
NEORAL
SANDIMMUNE
Click for Drug Monograph
, certain Ca channel blockers). Diets that alter the bacterial flora may markedly affect the overall metabolism of certain drugs. Some foods affect the body's response to drugs. For example, tyramine, a component of cheese and a potent vasoconstrictor, can cause hypertensive crisis in some patients who take monoamine oxidase inhibitors and eat cheese.

Nutritional deficiencies can affect drug absorption and metabolism. Severe energy and protein deficiencies reduce enzyme tissue concentrations and may impair the response to drugs by reducing absorption or protein binding and causing liver dysfunction. Changes in the GI tract can impair absorption and affect the response to a drug. Deficiency of Ca, Mg, or zinc may impair drug metabolism. Vitamin C deficiency decreases activity of drug-metabolizing enzymes, especially in the elderly.

Many drugs affect appetite, food absorption, and tissue metabolism (see Table 6: Nutrition: General Considerations: Effects of Some Drugs on Nutrition). Some drugs (eg, metoclopramide Some Trade Names
REGLAN
Click for Drug Monograph
) increase GI motility, decreasing food absorption. Other drugs (eg, opioids, anticholinergics) decrease GI motility. Some drugs are better tolerated if taken with food.

Certain drugs affect mineral metabolism. For example, diuretics, especially thiazides, and corticosteroids can deplete body K, increasing susceptibility to digoxin Some Trade Names
DIGITEK
LANOXIN
Click for Drug Monograph
-induced cardiac arrhythmias. Repeated use of laxatives may deplete K. Cortisol, desoxycorticosterone, and aldosterone cause marked Na and water retention, at least temporarily; retention is much less with prednisone Some Trade Names
DELTASONE
Click for Drug Monograph
, prednisolone Some Trade Names
ORAPRED
PRELONE
Click for Drug Monograph
, and some other corticosteroid analogs. Sulfonylureas and lithium Some Trade Names
ESKALITH
LITHOBID
LITHONATE
Click for Drug Monograph
can impair the uptake or release of iodine by the thyroid. Oral contraceptives can lower plasma zinc levels and increase copper levels. Certain antibiotics (eg, tetracyclines) reduce iron absorption, as can certain foods (eg, vegetables, tea, bran).

Certain drugs affect vitamin absorption or metabolism. Ethanol impairs thiamin utilization, and isoniazid Some Trade Names
INH
NYDRAZID
Click for Drug Monograph
interferes with niacin and pyridoxine metabolism. Ethanol and oral contraceptives inhibit folate absorption. Most patients receiving phenytoin Some Trade Names
DILANTIN
Click for Drug Monograph
, phenobarbital Some Trade Names
LUMINAL
Click for Drug Monograph
, primidone Some Trade Names
MYSOLINE
Click for Drug Monograph
, or phenothiazines develop folate deficiency, probably because hepatic microsomal drug-metabolizing enzymes are affected. Folate supplements may make phenytoin Some Trade Names
DILANTIN
Click for Drug Monograph
less effective. Anticonvulsants can cause vitamin D deficiency. Malabsorption of vitamin B₁₂ can occur with use of aminosalicylic acid, slow-release K iodide, colchicine Some Trade Names
No US trade name
Click for Drug Monograph
, trifluoperazine Some Trade Names
STELAZINE
Click for Drug Monograph
, ethanol, and oral contraceptives. Oral contraceptives with a high progestin dose can cause depression, probably because of metabolically induced tryptophan deficiency.

Table 6
Effects of Some Drugs on Nutrition Effect Drugs Increases appetite Alcohol, antihistamines, corticosteroids, dronabinol Some Trade Names MARINOL Click for Drug Monograph , insulin Some Trade Names HUMULIN NOVOLIN Click for Drug Monograph , megestrol Some Trade Names MEGACE Click for Drug Monograph acetate, mirtazapine Some Trade Names REMERON Click for Drug Monograph , many psychoactive drugs, sulfonylureas, thyroid hormone Decreases appetite Antibiotics, bulk agents (methylcellulose, guar gum), cyclophosphamide Some Trade Names CYTOXAN Click for Drug Monograph , digoxin Some Trade Names DIGITEK LANOXIN Click for Drug Monograph , glucagon, indomethacin Some Trade Names INDOCIN Click for Drug Monograph , morphine Some Trade Names DURAMORPH MS CONTIN MSIR ROXANOL Click for Drug Monograph , fluoxetine Some Trade Names PROZAC SARAFEM Click for Drug Monograph Decreases absorption of fats Orlistat Some Trade Names ALLI XENICAL Click for Drug Monograph Increases plasma glucose levels Octreotide Some Trade Names SANDOSTATIN Click for Drug Monograph , opioids, phenothiazines, phenytoin Some Trade Names DILANTIN Click for Drug Monograph , probenecid Some Trade Names No US trade name Click for Drug Monograph , thiazide diuretics, corticosteroids, warfarin Some Trade Names COUMADIN Click for Drug Monograph Decreases plasma glucose levels ACE inhibitors, aspirin Some Trade Names BUFFERIN ECOTRIN GENACOTE Click for Drug Monograph , barbiturates, β-blockers, insulin Some Trade Names HUMULIN NOVOLIN Click for Drug Monograph , monoamine oxidase inhibitors (MAOIs), oral antihyperglycemic drugs, phenacetin, phenylbutazone Some Trade Names No US trade name , sulfonamides Decreases plasma lipid levels Aspirin Some Trade Names BUFFERIN ECOTRIN GENACOTE Click for Drug Monograph and p-aminosalicylic acid, l- asparaginase Some Trade Names ELSPAR Click for Drug Monograph , chlortetracycline, colchicine Some Trade Names No US trade name Click for Drug Monograph , dextrans, glucagon, niacin Some Trade Names NIACOR NIASPAN SLO-NIACIN Click for Drug Monograph , phenindione, statins, sulfinpyrazone Some Trade Names No US trade name , trifluperidol Increases plasma lipid levels Adrenal corticosteroids, chlorpromazine Some Trade Names THORAZINE Click for Drug Monograph , ethanol, growth hormone, oral contraceptives (estrogen-progestin type), thiouracil, vitamin D Decreases protein metabolism Chloramphenicol Some Trade Names CHLOROMYCETIN Click for Drug Monograph , tetracycline Some Trade Names ACHROMYCIN V TETRACYN TETREX Click for Drug Monograph

Last full review/revision July 2007 by Margaret-Mary G. Wilson, MD

Content last modified July 2007