Interactions of food, nutrition, and drugs
Particular drugs can affect the nutritional state, changing the results of biochemical tests or even leading on occasions to clinical undernutrition, overnutrition, or malnutrition.
Appetite may be decreased
by anorectic drugs, bulking agents, dexamphetamine, metformin, cardiac glycosides, glucagon, morphine, phenylbutazone, indometacin, cyclophosphamide, fluorouracil, methylphenidate, salbutamol, levodopa, etc, and by drugs that alter taste (griseofulvin, penicillamine, and lincomycin).
Appetite may be increased
by sulphonylureas, oral contraceptives, cyproheptadine, chlorpromazine, androgens, anabolic steroids, corticosteroids, insulin, lithium, amitriptyline, pizotifen, clomipramine, benzodiazepines, and metoclopramide.
for more than one nutrient may be induced by neomycin, kanamycin, paromomycin, colchicine, phenindione, chlortetracycline, cholestyramine, colestipol,
cyclophosphamide, indometacin, liquid paraffin (fat soluble vitamins), methotrextate, and methyldopa.
Energy metabolism may be stimulated by caffeine, smoking, and some sympathomimetic drugs.
—Increased blood glucose concentrations may be produced by corticosteroids, thiazide diuretics, diazoxide, oral contraceptives, and phenytoin. Hypoglycaemia may be produced by propranolol and by alcohol (as well as by sulphonylureas, metformin and insulin).
Plasma total cholesterol may be raised by thiazides (for example, chlorthalidone, hydrochlorothiazide), by phenobarbital, chlorpromazine, some oral contraceptives, and large intakes of boiled coffee. As well as specific cholesterol lowering drugs, aspirin, colchicine, prazosin, clonidine, neomycin, phenformin, and sulphinpyrazone may lower total cholesterol.
Plasma high density lipoprotein cholesterol
may be raised by phenytoin, ethanol, cimetidine, valproate, carbamazine, terbutaline, and prazosin. It may be lowered by danazol, propranolol, and oxprenolol.
may be raised by propranolol, ethanol, and (oestrogenic) oral contraceptives. They may be lowered by norethisterone.
Nitrogen balance may be made negative by corticosteroids, vaccines, and tetracyclines. It may be made positive by insulin or anabolic steroids.
Plasma amino acids
may be increased by tranylcypromine and lowered by oral contraceptives. Plasma phenylalanine may be raised by trimethoprim and methotrexate.
absorption can be reduced by ethanol.
status may be lowered by oral contraceptives and by chlorpromazine.
may be antagonised by isoniazid.
may be antagonised by isoniazid, hydralazine, cycloserine, penicillamine, oral contraceptives, oestrogens, hydrocortisone, imipramine, levodopa, piperazine, and pyrazinamide.
may be antagonised by ethanol, phenytoin, oral contraceptives (uncommonly), cycloserine, triamterine, and cholestyramine. In addition several drugs owe their antibacterial action to antagonism of folate metabolism—more in microbial than mammalian cells— pyrimethamine, trimethoprin, and pentamidine. Methotrexate is a potent folate antagonist which has more effect on rapidly dividing cells—for example, cancer cells.
absorption may be impaired by slow K, cimetidine, ranitidine, metformin, colchicine, trifluroperazine, and by high doses of vitamin C, cholestyramine, and methotrexate. Prolonged nitrous oxide anaesthesia oxidizes vitamin B-12 . Smoking and oral contraceptives reduce the plasma concentration.
Plasma concentrations are lowered by oral contraceptives, smoking, aspirin, and tetracycline. Ascorbate excretion is increased by corticosteroids, phenylbutazone and sulfinpyrazone.
plasma concentration is increased by oral contraceptives. Absorption may be reduced by liquid paraffin and cholestyramine.
status is lowered by anticonvulsants—for example, phenytoin, phenobarbitone, and when these are taken in high dose for long periods rickets can occur.
is antagonised by iron in premature newborns. Fish oils (refined) increase requirements.
Coumarin drugs—for example warfarin—are antimetabolites. Purgatives and intestinal antibiotics, such as neomycin, tetracyclines, and sulphonamides, may remove the contribution from colonic bacteria. Salicylates and cholestyramine may reduce absorption, and some cephalosporin antibiotics antagonise the vitamin K-epoxide cycle.
—Drugs are important causes of potassium depletion: purgatives and laxatives increase faecal loss; thiazide diuretics and frusemide and ethacrynic acid increase renal loss.
Other drugs that may increase urinary potassium are penicillin, glucocorticoids, liquorice, outdated tetracycline, gentamicin, and alcohol. Insulin can lower serum potassium. Drugs that
raise serum potassium include ACE inhibitors, spironolactone, succinylcholine, triamterene, and potassium compounds.
—Absorption may be increased by aluminium hydroxide or by cholestyramine and decreased by phosphates and corticosteroids. Thiazide diuretics decrease urinary calcium excretion. Gentamicin, dactinomycin, frusemide, and ethacrynic acid increase it.
—Gastrointestinal bleeding from aspirin depletes the body’s iron. Allopurinol, fructose, and ascorbic acid increase absorption. Antacids, phosphates, and tetracycline decrease it. Oral contraceptives tend to increase serum iron.
—Sulphonylureas, phenylbutazone, amiodorone, and lithium can cause goitre; they interfere with iodine uptake in the gland. Serum protein bound iodine is increased by oral contraceptives, x-ray contrast media, and potassium iodide, and decreased by phenytoin.
absorption is decreased by aluminium or calcium compounds.
Zinc depletion from increased urinary excretion may be produced by thiazide diuretics and frusemide, by cisplatin, penicillamine, and alcohol.
depletion from increased urinary loss may be produced by thiazides and frusemide, cisplatin, alcohol, aminoglycosides, amphotericin, ciclosporin, and gentamicin.
Nutrients, foods, and drugs can interact in several ways
Foods can affect drugs, for example, by affecting absorption, an acute effect of single meals. Grapefruit juice inhibits one of the cytochrome P450s that metabolises drugs such as
calcium-channel blockers, statins, carbamazepine, and terfenadine.
Nutrition can affect drugs. The nutritional state can affect drug metabolism and hence dosage and toxicity, for example, in Kwashiorkor.
Particular drugs can affect the nutritional state. Appetite, absorption, metabolism, and concentration of nutrients can be affected, positively or negatively, by different drugs.
Drugs can cause unpleasant reactions to minor components in some foods whose metabolism we normally take for granted— for example, hypertension from tyramine in cheese in patients taking monoamine oxidase inhibitors.
A few drugs are used as drinks, as part of the usual diet: alcoholic drinks, coffee, tea, and carbonated cola beverages.
Some nutrients are used as drugs. The nutrients are all obtainable in pure form. They may, in doses above the nutrient requirement, sometimes have a useful pharmacological action—for example, nicotinic acid for hyperlipidaemia.
When to take medicines
Most drugs are best taken with or just after meals, because this is the easiest way to remember to take any drug and some are gastric irritants. Absorption of several drugs is a little delayed but this is unimportant and a few are better absorbed when taken with meals—for example, griseofulvin, metoprolol, and labetalol.
Plenty of water should be taken with uricosurics (to prevent renal precipitation) and with cholestyramine and bulk formers like methyl cellulose.
A few drugs should be taken half an hour before meals: antibiotics which are labile in acid—ampicillin, benzylpenicillin, cloxacillin, erythromycin, lincomycin, tetracycline, rifampicin,
and isoniazid. So should one of the antidiabetic agents— glipizide—and, of course, appetite suppressant drugs.