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• Nutrition: General Considerations
4

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, amiodaroneSome Trade Names
CORDARONE
Click for Drug Monograph
, carbamazepineSome Trade Names
TEGRETOL
Click for Drug Monograph
, cyclosporineSome 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, metoclopramideSome 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 digoxinSome 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 prednisoneSome Trade Names
DELTASONE
Click for Drug Monograph
, prednisoloneSome Trade Names
ORAPRED
PRELONE
Click for Drug Monograph
, and some other corticosteroid analogs. Sulfonylureas and lithiumSome Trade Names
ESKALITH
LITHOBID
LITHONATE
Click for Drug Monograph
can impair the uptake or release of iodine by the thyroid. Oral contraceptives can lower blood 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 isoniazidSome Trade Names
INH
NYDRAZID
Click for Drug Monograph
interferes with niacin and pyridoxine metabolism. Ethanol and oral contraceptives inhibit folate absorption. Most patients receiving phenytoinSome Trade Names
DILANTIN
Click for Drug Monograph
, phenobarbitalSome Trade Names
LUMINAL
Click for Drug Monograph
, primidoneSome Trade Names
MYSOLINE
Click for Drug Monograph
, or phenothiazines develop folate (folic acid) deficiency, probably because hepatic microsomal drug-metabolizing enzymes are affected. Folate supplements may make phenytoinSome 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, colchicineSome Trade Names
No US trade name
Click for Drug Monograph
, trifluoperazineSome 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, dronabinolSome Trade Names MARINOL Click for Drug Monograph , insulinSome Trade Names HUMULIN NOVOLIN Click for Drug Monograph , megestrolSome Trade Names MEGACE Click for Drug Monograph acetate, mirtazapineSome Trade Names REMERON Click for Drug Monograph , many psychoactive drugs, sulfonylureas, thyroid hormone Decreases appetite Antibiotics, bulk agents (methylcellulose, guar gum), cyclophosphamideSome Trade Names CYTOXAN Click for Drug Monograph , digoxinSome Trade Names DIGITEK LANOXIN Click for Drug Monograph , glucagon, indomethacinSome Trade Names INDOCIN Click for Drug Monograph , morphineSome Trade Names DURAMORPH MS CONTIN MSIR ROXANOL Click for Drug Monograph , fluoxetineSome Trade Names PROZAC SARAFEM Click for Drug Monograph Decreases absorption of fats OrlistatSome Trade Names ALLI XENICAL Click for Drug Monograph Increases blood glucose levels OctreotideSome Trade Names SANDOSTATIN Click for Drug Monograph , opioids, phenothiazines, phenytoinSome Trade Names DILANTIN Click for Drug Monograph , probenecidSome Trade Names No US trade name Click for Drug Monograph , thiazide diuretics, corticosteroids, warfarinSome Trade Names COUMADIN Click for Drug Monograph Decreases blood glucose levels ACE inhibitors, aspirinSome Trade Names BUFFERIN ECOTRIN GENACOTE Click for Drug Monograph , barbiturates, β-blockers, insulinSome Trade Names HUMULIN NOVOLIN Click for Drug Monograph , monoamine oxidase inhibitors (MAOIs), oral antihyperglycemic drugs, phenacetin, phenylbutazoneSome Trade Names No US trade name , sulfonamides Decreases blood lipid levels AspirinSome Trade Names BUFFERIN ECOTRIN GENACOTE Click for Drug Monograph and p-aminosalicylic acid, l-asparaginaseSome Trade Names ELSPAR , chlortetracycline, colchicineSome Trade Names No US trade name Click for Drug Monograph , dextrans, glucagon, niacinSome Trade Names NIACOR NIASPAN SLO-NIACIN Click for Drug Monograph , phenindione, statins, sulfinpyrazoneSome Trade Names No US trade name , trifluperidol Increases blood lipid levels Adrenal corticosteroids, chlorpromazineSome Trade Names THORAZINE Click for Drug Monograph , ethanol, growth hormone, oral contraceptives (estrogen-progestin type), thiouracil, vitamin D Decreases protein metabolism ChloramphenicolSome Trade Names CHLOROMYCETIN Click for Drug Monograph , tetracyclineSome 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