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, carbamazepine, cyclosporine, certain calcium channel blockers, statins). 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 tissue enzyme concentrations and may impair the response to drugs by reducing absorption or protein binding and causing liver dysfunction. Changes in the gastrointestinal tract can impair absorption and affect the response to a drug. Deficiency of calcium, magnesium, or zinc may impair drug metabolism. Vitamin C deficiency decreases activity of drug-metabolizing enzymes, especially in older people.
Many drugs affect appetite, food absorption, and tissue metabolism (see table Effects of Some Drugs). Some drugs (eg, metoclopramide) increase gastrointestinal motility, decreasing food absorption. Other drugs (eg, opioids, anticholinergics) decrease gastrointestinal motility. Some drugs are better tolerated if taken with food.
Effects of Some Drugs on Appetite, Food Absorption, and Metabolism
Drugs | Effect |
|---|---|
Alcohol, antihistamines, corticosteroids, dronabinol, insulin, megestrol acetate, mirtazapine, many psychoactive drugs, sulfonylureas, thyroid hormone | Increases appetite |
Some antibiotics, bulk agents (methylcellulose, guar gum), cyclophosphamide, digoxin, glucagon, indomethacin, morphine, fluoxetine | Decreases appetite |
Orlistat | Decreases absorption of fats |
Octreotide, opioids, phenothiazines, second-generation antipsychotics, phenytoin, probenecid, thiazide diuretics, corticosteroids, warfarin | Increases blood glucose levels |
Angiotensin-converting enzyme (ACE) inhibitors, aspirin, barbiturates, beta-blockers, insulin, monoamine oxidase inhibitors (MAOIs), oral antihyperglycemic drugs, phenacetin, phenylbutazone, sulfonamides | Decreases blood glucose levels |
Aspirin andp-aminosalicylic acid, L-asparaginase, chlortetracycline, colchicine, dextrans, glucagon, niacin, phenindione, statins, sulfinpyrazone, trifluperidol | Decreases blood lipid levels |
Adrenal corticosteroids, chlorpromazine, some second-generation antipsychotics, ethanol, growth hormone, oral contraceptives (estrogen-progestin type), thiouracil, vitamin D | Increases blood lipid levels |
Chloramphenicol, tetracycline | Decreases protein metabolism |
Certain drugs affect mineral metabolism (see table Possible Effects of Drugs on Mineral Metabolism). Certain antibiotics (eg, tetracyclines) reduce iron absorption, as can certain foods (eg, vegetables, tea, bran).
Possible Effects of Drugs on Mineral Metabolism
Drugs | Effects |
|---|---|
Diuretics, especially thiazides, and corticosteroids | Can deplete body potassium* |
Laxatives if used repeatedly | May deplete potassium* |
Cortisol, desoxycorticosterone, and aldosterone† | Cause marked sodium and water retention, at least temporarily |
Sulfonylureas and lithium | Impair uptake or release of iodine by the thyroid |
Oral contraceptives | Lower blood zinc levels, increase copper levels |
Certain antibiotics (eg, tetracyclines) | Reduce iron absorption |
*Depletion of potassium increases susceptibility to digoxin-induced cardiac arrhythmias. | |
†Retention of sodium and water is much less with prednisone, prednisolone, and some other corticosteroid analogs. | |
Certain drugs affect vitamin absorption or metabolism (see table Possible Effects of Drugs on Vitamin Absorption or Metabolism).
Possible Effects of Drugs on Vitamin Absorption or Metabolism
Drugs | Effects |
|---|---|
Ethanol | Impairs thiamin utilization |
Isoniazid | Interferes with niacinand pyridoxine metabolism |
Ethanol and oral contraceptives | Inhibit folate absorption |
Phenytoin, phenobarbital, primidone, or phenothiazines | In most patients, cause folate (folic acid) deficiency*, probably because hepatic microsomal drug-metabolizing enzymes are affected |
Antiseizure drugs (eg, carbamazepine, phenobarbital, phenytoin) | Can decrease vitamin D metabolism |
Aminosalicylic acid, slow-release potassium iodide, colchicine, trifluoperazine, metformin, ethanol, and oral contraceptives | Interfere with absorption of vitamin B12 |
Oral contraceptives with a high progestin dose | Can cause depression, probably because of metabolically induced tryptophan deficiency |
Proton pump inhibitors | Can decrease absorption of vitamin B12, vitamin C, iron, calcium, and magnesium |
*Folate supplements may make phenytoin less effective. | |
