Drug Interactions

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Drug interactions

Definition

Drug interactions are changes in the effect of one drug due to the effect of either another drug taken at the same time (drug-drug interactions) or food consumed while the drug is being taken (drug-food interactions).

Description

Some drugs are deliberately combined for administration because there are beneficial effects to be derived. Generally, drug interactions are unwanted and harmful. They may either serve to intensify or diminish the desired effect of a particular drug, or worsen its side effects. Although most drug-drug interactions involve prescription drugs, they can occur with nonprescription or over-the-counter (OTC) medications—the most common of these being aspirin, antacids , and decongestants.

**Common over-the-counter drug interaction warnings**
Category	Drug interaction information
(Illustration by GGS Information Services. Cengage Learning, Gale.)
Acid reducers	For products containing cimetidine, ask a doctor or pharmacist before use if you are:
H2 Receptor Antagonists (drugs that prevent or relieve heartburn associated with acid indigestion and sour stomach)	taking theophylline (oral asthma drug), warfarin (blood thinning drug), or phenytoin (seizure drug)
Antacids (drugs for relief of acid indigestion, heartburn, and/or sour stomach)	Ask a doctor or pharmacist before use if you are: allergic to milk or milk products if the product contains more than 5 grams lactose in a maximum daily dose taking a prescription drug Ask a doctor before use if you have: kidney disease
Antiemetics (drugs for prevention or treatment of nausea, vomiting, or dizziness associated with motion sickness)	Ask a doctor or pharmacist before use if you are: taking sedatives or tranquilizers Ask a doctor before use if you have: a breathing problem, such as emphysema or chronic bronchitis glaucoma difficulty in urination due to an enlarged prostate gland When using this product: avoid alcoholic beverages
Antihistamines (drugs that temporarily relieve runny nose or reduce sneezing, itching of the nose or throat, and itchy watery eyes due to hay fever or other upper respiratory problems)	Ask a doctor or pharmacist before use if you are taking: sedatives or tranquilizers a prescription drug for high blood pressure or depression Ask a doctor before use if you have: glaucoma or difficulty in urination due to an enlarged prostate gland breathing problems, such as emphysema, chronic bronchitis, or asthma When using this product: alcohol, sedatives, and tranquilizers may increase drowsiness avoid alcoholic beverages
Antitussives Cough medicine (drugs that temporarily reduce cough due to minor throat and bronchial irritation as may occur with a cold)	Ask a doctor or pharmacist before use if you are: taking sedatives or tranquilizers Ask a doctor before use if you have: glaucoma or difficulty in urination due to an enlarged prostate gland
Bronchodilators (drugs for the temporary relief of shortness of breath, tightness of chest and wheezing due to bronchial asthma)	Ask a doctor before use if you: have heart disease, high blood pressure, thyroid disease, diabetes, or difficulty in urination due to an enlarged prostate gland have ever been hospitalized for asthma or are taking a prescription drug for asthma
Laxatives (drugs for the temporary relief of constipation)	Ask a doctor before use if you have: kidney disease and the laxative contains phosphates, potassium, or magnesium stomach pain, nausea, or vomiting
Nasal decongestants (drugs for the temporary relief of congestion due to a cold, hay fever, or other upper respiratory allergies)	Ask a doctor before use if you: have heart disease, high blood pressure, thyroid disease, diabetes, or difficulty in urination due to an enlarged prostate gland
Nicotine replacement products (drugs that reduce withdrawal symptoms associated with quitting smoking, including nicotine craving)	Ask a doctor before use if you: have high blood pressure not controlled by medication have heart disease or have had a recent heart attack or irregular heartbeat, since nicotine can increase your heart rate Ask a doctor or pharmacist before use if you are: taking a prescription drug for depression or asthma (your dose may need to be adjusted) using a prescription non-nicotine stop smoking drug Do not use: if you continue to smoke, chew tobacco, use snuff, or use other nicotine-containing products

Individuals under the care of more than one health care practitioner are at highest risk for drug interactions because each practitioner may not be aware of drugs being prescribed by the other. The patient needs to make each practitioner fully aware of all medications being taken. This includes

**Common over-the-counter drug interaction warnings**
Category	Drug interaction information
Be sure to read the warnings on the actual product label before taking any over-the-counter drugs.
source: Council on Family Health, in cooperation with the National Consumers League and the Food and Drug Administration, U.S. Department of Health
(Illustration by GGS Information Services. Cengage Learning, Gale.)
Nighttime sleep aids (drugs for relief of occasional sleeplessness)	Ask a doctor or pharmacist before use if you are: taking sedatives or tranquilizers Ask a doctor before use if you have: a breathing problem such as emphysema or chronic bronchitis glaucoma difficulty in urination due to an enlarged prostate gland When using this product: avoid alcoholic beverages
Pain relievers (drugs for the temporary relief of minor body aches, pains, and headaches)	Ask a doctor before taking if you: consume three or more alcohol-containing drinks per day (The following ingredients are found in different OTC pain relievers: acetaminophen, aspirin, ibuprofen, ketoprofen, magnesium salicylate, and naproxen. It is important to read the label of pain reliever products to learn about different drug interaction warnings for each ingredient.)
Stimulants (drugs that help restore mental alertness or wakefulness during fatigue or drowsines)	When using this product: limit the use of foods, beverages, and other drugs that have caffeine. Too much caffeine can cause nervousness, irritability, sleeplessness, and occasional rapid heart beat be aware that the recommended dose of this product contains about as much caffeine as a cup of coffee

prescription and nonprescription medications, and herbal remedies. A practitioner may not think to ask a patient about OTC medications or herbal supplements, and the patient may not think to inform their practitioner they are taking these substances because they do not think of OTCs or herbals as medications. The more drugs being consumed, the greater the risk of developing a drug interaction. This risk also increases with the amount of drug taken and the tendency of particular drugs to interact adversely with each other. The incidence of adverse drug reactions increases with the age of the patient; the risk is three times greater for older people than for younger adults.

When the effect of one drug in the body is altered by the presence of another, one drug may increase or decrease the effects of the other with harmful results. Two drugs taken together may produce a new and dangerous reaction, or they may be in opposition to each other in their actions. Two similar drugs taken together may produce an effect that is greater than would be expected from one drug. This effect is called potentiation. One drug may also affect the rate at which the kidneys excrete another drug by altering the acidity of the urine. This, in turn, affects the excretion of other drugs. Vitamin C in large doses can do this. Although not considered a drug by some, alcohol is a drug that does affect bodily processes and is often responsible for drug interactions. OTC drugs can interact with each other as well as with prescription drugs. For example, many cough medicines contain alcohol which, if taken with antihistamine medications, could increase sleepiness and decrease alertness.

Examples of drug interactions include:

salt substitutes interacting with potassium-sparing diuretics (agents that promote urine secretion) to increase blood potassium levels and cause nausea, vomiting, diarrhea, muscle weakness, and possibly cardiac arrest
decongestants interacting with diuretics to increase blood pressure
antacids interacting with anticoagulants (blood thinning drugs) to slow down absorption of the prescribed drug or interacting with absorption of other drugs—such as the antibiotic tetracycline—and thus prolonging an infection
aspirin increasing the effect of blood thinning drugs
antihistamines increasing the sedative effects of barbiturates (sleeping pills), tranquilizers, and some pain relievers
iron supplements binding with antibiotics in the stomach, preventing absorption of the antibiotic into the bloodstream
antihypertensive medications mixed with digitalis (Lanoxin) resulting in abnormal heart rhythms
anticoagulants mixed with sleeping pills resulting in decreased effectiveness of the anticoagulant
antibiotics taken by women on the low-dose birth control pill causing decreased effectiveness of the pill
nonsteroidal antiinflammatory drugs (NSAIDs) causing the body to retain salt and fluid that can oppose or antagonize the effectiveness of a diuretic
beta-blockers, such as propanolol, counteracting certain drugs taken for asthma

Certain drug-food combinations can produce dangerous side effects as well. Food can speed up or slow down the action of a medication, and some drugs may prevent the absorption of vitamins and minerals from food. Drugs may also alter the way the body uses nutrients, as well as altering the taste sensation. Chemicals in cigarette smoke can increase the enzyme activity of some liver enzymes, which, in turn, reduces the effectiveness of some pain relievers and some drugs used for lung conditions. The antibiotic tetracycline is not absorbed appropriately if it is taken within an hour of drinking milk or eating other dairy products or foods containing calcium .

To help avoid drug interactions, patients should inform their health care practitioners of any medical problems they have or have had, maintain a list of drugs—both prescription and nonprescription—taken during the few weeks prior to their visit to their practitioner, and give the list to their practitioner. They should also advise their practitioner of any allergies or unusual reactions to drugs, food, or other substances, and make note of any special dietary or food restrictions. A woman should always inform her practitioner if she is pregnant, plans to become pregnant in the near future, and if breastfeeding.

Viewpoints

Although drug interactions can create serious health risks, they can be avoided with appropriate education (of the patient) and history-taking (by the health care practitioner). The health care practitioner needs to take the time to ask pertinent questions about an individual's history, including diet , nutritional intake, and medication regimen which should include nonprescription drugs and herbal remedies. Although it is often difficult for the practitioner to spend an appropriate amount of time with patients in this era of health care management, it could ultimately save time and money and prevent serious consequences to the health of the patient. Healthcare providers need to stay informed and up-to-date regarding drug-drug and drug-food interactions.

KEY TERMS

Potentiation —Making effective or active, or more effective or active; synergistically augmenting the activity of one drug with another.

Professional implications

Health care professionals are capable of exerting a measurable impact on the lives of individuals who are taking drugs for either medical or nonmedical reasons. Education is the foundation for patient care with regards to potential drug interactions. It is the responsibility of the care provider to take the time to inform patients of potential interactions with drugs and food, as well as to take a complete patient history.

A patient's family should be included in the educational process so they may recognizing possible interactions by changes in behavioral patterns or demeanor.