Pharmaceutical Drug Interactions

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I have been doing a lot of research lately, trying to help my Dad heal. In doing so, I have found some interesting articles. Blessings, Joy

Drug Interactions

The effect a drug has on a person may be different than expected because that drug interacts with

Another drug the person is taking (drug-drug interaction) Food, beverages, or supplements the person is consuming (drug-nutrient interaction) Another disease the person has (drug-disease interaction).

The effects of drug interactions are usually unwanted and sometimes harmful. Interactions may increase or decrease the actions of one or more drugs, resulting in side effects or failed treatment.

Drug-Drug Interactions

Drug-drug interactions can involve prescription or nonprescription (over-the-counter) drugs. Types of drug-drug interactions include duplication, opposition (antagonism), and alteration of what the body does to one or both drugs.

Duplication: When two drugs with the same effect are taken, their side effects may be intensified. Duplication may occur when people inadvertently take two drugs (often at least one is an over-the-counter drug) that have the same active ingredient. For example, people may take a cold remedy and a sleep aid, both of which contain diphenhydramine , or a cold remedy and a pain reliever, both of which contain acetaminophen . This type of duplication is particularly likely with the use of drugs that contain multiple ingredients or that are sold under brand names (thus appearing to be different but actually containing the same ingredients). Awareness of drug ingredients is important, as is checking each new drug to avoid duplication. For example, many prescription-strength pain relievers contain an opioid plus acetaminophen . People taking such a product who do not know its ingredients might take over-the-counter acetaminophen for extra relief, risking toxicity.

Some Trade Names TYLENOLSome Trade Names BENADRYLNYTOLSOMINEX

Similar problems with duplication can arise when two different drugs with the same effect are taken. This is most likely to occur when people see several doctors, obtain prescriptions at more than one pharmacy, or both. Doctors who are not aware of what others have prescribed may inadvertently prescribe similar drugs. For example, excessive sedation and dizziness can occur when two doctors both prescribe a sleep aid or when one prescribes a sleep aid and the other prescribes another drug (such as an antianxiety drug) that has similar sedative effects. People can reduce this risk by keeping each doctor informed about all drugs being taken and by using one pharmacy to obtain all prescriptions. It is helpful to keep an up-to-date written list of all drugs being taken and to bring the list along on each doctor visit. Also, people should not take previously prescribed drugs (such as a sleeping pill or pain reliever) without checking with the doctor or pharmacist because that drug may duplicate or otherwise interact with one of their current drugs.

Opposition (Antagonism): Two drugs with opposing actions can interact, thereby reducing the effectiveness of one or both. For example, nonsteroidal anti-inflammatory drugs (NSAIDs—see Pain: Nonsteroidal Anti-Inflammatory Drugs), such as ibuprofen , which are taken to relieve pain, may cause the body to retain salt and fluid. Diuretics, such as hydrochlorothiazide and furosemide , help rid the body of excess salt and fluid. If a person takes both types of drug, the NSAID may reduce the diuretic's effectiveness. Certain beta-blockers (such as propranolol ), taken to control high blood pressure and heart disease, counteract beta-adrenergic stimulants, such as albuterol , taken to manage asthma. Both types of drugs target the same cell receptors—beta-2 receptors (see ), but one type blocks them, and the other stimulates them.

Some Trade Names INDERALSome Trade Names ADVILMOTRINNUPRINSome Trade Names LASIXSome Trade Names ESIDRIXHydroDIURILORETIC

Some Trade Names PROVENTILVENTOLIN

Alteration: One drug may alter how the body absorbs, distributes, metabolizes, or excretes another drug.

How to Reduce the Risk of Drug-Drug Interactions

Consult the doctor or pharmacist before taking any new drugs, including over-the-counter drugs and dietary supplements, such as medicinal herbs. Keep a list of all drugs being taken. Periodically discuss this list with the doctor or pharmacist. Keep a list of all disorders. Periodically discuss this list with the doctor. Select a pharmacy that provides comprehensive services (including checking for possible interactions) and that maintains a complete drug profile for each person. Have all prescriptions dispensed in this pharmacy. Learn about the purpose and actions of all drugs prescribed. Learn about the possible side effects of the drugs. Learn how to take the drugs, what time of day they should be taken, and whether they can be taken during the same time period as other drugs. Review the use of over-the-counter drugs with the pharmacist. Discuss any disorders present and any prescription drugs being taken. Take drugs as instructed. Report to the doctor or pharmacist any symptoms that might be related to the use of a drug. If seeing more than one doctor, make sure each doctor knows all the drugs being taken.

Acid-blocking drugs, such as histamine-2 (H2) blockers and proton pump inhibitors, raise the pH of the stomach and decrease absorption of some drugs, such as ketoconazole , a drug for fungal infections.

Some Trade Names NIZORAL

Many drugs are broken down and inactivated (metabolized) by certain enzymes in the liver. Some drugs affect these liver enzymes, either increasing or decreasing their activity, and may cause another drug to be inactivated more quickly or more slowly than usual. For example, by increasing the activity of liver enzymes, barbiturates such as phenobarbital cause the anticoagulant warfarin to be inactivated more quickly and thus to be less effective when taken during the same time period.

Some Trade Names LUMINAL

Conversely, by decreasing the activity of the enzyme system, drugs such as erythromycin and ciprofloxacin can increase the activity of warfarin , risking bleeding. When drugs that affect liver enzymes are used in people taking warfarin , doctors monitor the people more closely and adjust the dose of warfarin to compensate for this effect. The warfarin dose is adjusted again when other drugs are stopped. Many other drugs affect liver enzymes.

Some Trade Names CILOXANCIPROSome Trade Names E-MYCINERYTHROCINILOSONE

Some Trade Names COUMADIN

Chemicals in cigarette smoke can increase the activity of some liver enzymes. As a result, smoking decreases the effectiveness of some drugs, including propoxyphene (an analgesic) and theophylline (a drug that widens the airways called a bronchodilator).

Some Trade Names DARVONDOLENE

Some Trade Names BRONKODYLTHEOLAIR

Some drugs affect the rate at which the kidneys excrete another drug. For example, large doses of vitamin C increase the urine's acidity and thus may change the rate of excretion and activity of certain drugs. For example, the rate of excretion may be decreased for acidic drugs such as aspirin but may be increased for basic drugs such as pseudoephedrine .

Some Trade Names AFRINOLSUDAFEDSome Trade Names ECOTRINASPERGUM

Because there are so many drug interactions, many doctors and pharmacists reduce the risk of problems by checking reference books and computer software programs when prescribing or dispensing prescriptions for additional drugs. In most pharmacies, drug orders and prescriptions are reviewed using a computer system that automatically checks for drug interactions.

Drug-Nutrient Interactions

Nutrients include food, beverages (including alcohol), and dietary supplements. Consumption of these substances may alter the effects of drugs the person takes.

Food: Like food, drugs taken by mouth must be absorbed through the lining of the stomach or the small intestine. Consequently, the presence of food in the digestive tract may reduce absorption of a drug. Often, such interactions can be avoided by taking the drug 1 hour before or 2 hours after eating.

Dietary Supplements: Dietary supplements, including medicinal herbs, are products (besides tobacco) that contain a vitamin, mineral, herb, or amino acid and that are intended as a supplement to the normal diet (see Medicinal Herbs and Nutraceuticals: Introduction). Supplements are regulated as foods, not as drugs, so they are not tested as comprehensively. However, they may interact with prescription or over-the-counter drugs. People who take dietary supplements should tell their doctors and pharmacists, so that interactions can be avoided.

Alcohol: Although many people do not consider alcohol a nutrient, it affects body processes and interacts with many drugs. For example, taking alcohol with the antibiotic metronidazole can cause flushing, headache, palpitations, and nausea and vomiting. Doctors or pharmacists can answer questions about possible alcohol and drug interactions.

Some Trade Names FLAGYL

Some Drug-Food Interactions

Affected Drug

Interacting Food

Interaction

Bisphosphonates (such as alendronate , ibandronate, and risedronate)Some Trade Names FOSAMAX

Any food

Food, even orange juice, coffee, or mineral water, may markedly reduce the absorption and effectiveness of these drugs. Alendronate and risedronate must be taken with plain water at least ½ hour before the first food, beverage, or drug of the day is taken, and ibandronate must be taken at least 1 hour before.

AnticoagulantsSome Trade Names COUMADIN

Foods high in vitamin K (such as broccoli, brussels sprouts, spinach, and kale)

Such foods may reduce the effectiveness of anticoagulants (such as warfarin ), increasing the risk of clotting. Intake of such foods should be limited, and the amount consumed daily should remain constant.

Certain benzodiazepines (such as triazolam) Calcium channel blockers (such as felodipine, nifedipine, and nisoldipine) Cyclosporine Estrogen and oral contraceptives Certain statins (such as atorvastatin, lovastatin, and simvastatin)

Grapefruit juice

Grapefruit juice inhibits enzymes involved in drug metabolism and thereby intensifies the effect of certain drugs, many of which are not listed here.

Digoxin

Some Trade Names LANOXIN

Oatmeal

The fiber in oatmeal and other cereals, when consumed in large amounts, can interfere with the absorption of digoxin .

MAO inhibitors (such as phenelzine and tranylcypromine )Some Trade Names PARNATESome Trade Names NARDIL

Foods high in tyramine, including many cheeses (such as American processed, cheddar, blue, brie, mozzarella, and Parmesan), yogurt, sour cream, cured meats (such as sausage and salami), liver, dried fish, caviar, avocados, bananas, yeast extracts, raisins, sauerkraut, soy sauce, fava beans, red wine, certain beers, and products containing caffeine

Severe headache and a potentially fatal increase in blood pressure (hypertensive crisis) can occur if people taking an MAO inhibitor (used most often to treat depression) consume these foods. These foods must be avoided.

Tetracycline

Some Trade Names ACHROMYCIN VTETRACYNSUMYCIN

Calcium or foods containing calcium, such as milk and other dairy products

These foods can reduce the absorption of tetracycline , which should be taken 1 hour before or 2 hours after eating.

MAO = monoamine oxidase.

Drug-Disease Interactions

Sometimes, drugs that are helpful in one disease are harmful in another disorder. For example, some beta-blockers taken for heart disease or high blood pressure can worsen asthma and make it hard for people with diabetes to tell when their blood sugar is too low. Some drugs taken to treat a cold may worsen glaucoma. People should tell their doctor all of the diseases they have before the doctor prescribes a new drug. Diabetes, high or low blood pressure, an ulcer, glaucoma, an enlarged prostate, poor bladder control, and insomnia are particularly important, because people with such diseases are more likely to have a drug-disease interaction.

Drug-disease interactions can occur in any age group but are common among older people, who tend to have more diseases (see Aging and Drugs).

Last full review/revision April 2007 by A. Hussar, PhD

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