Drug interaction --wlg 410
West Virginia University
Chris Raich, Pharm. D. candidate
; Marie Abate, Pharm. D.
Teri Dunsworth, Pharm. D.
, WVU School of Pharmacy
Drug interactions is a topic that usually conjures up
How big a problem are drug interactions?
feelings of fearfulness and helplessness. As a group leader,you can help others understand useful points about drug
Americans filled a record 2.4 billion prescriptions in 1996.
interactions and answer some important questions they
Although this may be seen as a good thing, it also can
may have. This information will help you inform
present problems. There has never before been so much
participants about harmful drug interactions. The goals of
opportunity for confusion, drug interactions, side effects,
and the improper use of medications. In addition:
• to help participants understand what drug interactions
Americans over age 65 comprise 12 percent of the
population, but they consume about 30 percent of all
• to help participants learn where they can get help and
prescription drugs and 40 percent of over-the-counter
• to give participants important tips to help prevent
When two to four different drugs are taken, the
potential for interaction is 6 percent, but the riskincreases to 50 percent with five drugs and to almost100 percent with eight drugs.
What is a drug interaction?
The average older person takes four or five drugs daily.
Drug interactions are responsible for 3 percent to 10
Before continuing, ask participants such questions as:
percent of admissions of older patients to the hospital,
“How would you define a drug interaction?” and “Do you
which costs an estimated $20 million annually in the
know of any specific drug interactions?” This will help
you to get an idea of what they may know or what they aremost interested in learning more about.
These facts illustrate the importance of everyone (andespecially older people) being knowledgeable about drug
Simply put, a drug interaction is a change in one drug’s
effect when administered with another drug, food, or othersubstance. For example, two or more drugs taken togethercan change the way a drug works in your body. This
How do drugs interact?
possibly could make one or more of the drugs less safe orcould cause them not to work as they should.
When we swallow a pill or tablet, most of us don’t thinkabout what happens to it. However, for a drug to work, it
It is important to know a little about the difference between
has to get into the bloodstream from the stomach and gut
a drug interaction and a side effect. A side effect, also
and then go to where it is needed in the body.
known as an adverse effect, is caused by a single
Side effects can occur with the normal use of a drug and
(It may help to draw a rough picture of the following
sometimes can be predicted and treated. A side effect, if
example for the participants: An example is the use of an
severe enough, may require your doctor to stop the drug or
antibiotic for pneumonia. After the pill is swallowed, it
lower the dosage. An example of a side effect is the
enters the gut. Here, it is absorbed through the gut lining
drowsiness caused by certain antihistamines.
and passes into the blood. Absorption is the way in which adrug travels from the gut into the bloodstream. Without
A drug interaction is caused by two or more
absorption, drugs taken by mouth would have no effect;
or other substances taken by the same person. A drug
the drugs would just pass right through the gut and out of
interaction may require your doctor to stop one or more of
the body. After the drug reaches the blood, it travels
the drugs. Always check with your doctor or pharmacist if
throughout the body and finally reaches the lungs, where it
you have any concerns, since it is often hard to tell if
symptoms are caused by a side effect, drug interaction,or disease.
During the time the drug travels in the blood, the body seesthe drug as something that normally doesn’t belong there.
As a result, the body tries to rid itself of the drug. This is
What are some factors that put one at
the reason why we have to take drugs every day,
higher risk for drug interactions?
sometimes many times a day. While a drug is going in, thebody is working to send it back out. The body has several
Not everyone is equally likely to experience a drug
methods for removing drugs. First, it can break down the
interaction when taking multiple drugs. Some people may
drug into parts, which then can be easily removed via the
get a serious reaction, but others may experience very mild
urine or feces. This action usually is performed by the
or no symptoms. Below are several reasons why some
liver. Second, the body can remove intact drugs by
experience drug interactions more than others
excreting them into the urine, which then is passed out.
do. It is important to watch for these factors in others or
This method is performed by the kidneys.
ourselves. For each risk factor, ask lesson participants whyit might help cause a drug interaction.
Some drugs can speed up or slow down the rate at whichthe liver and kidneys work to rid the body of other drugs.
1. Having multiple diseases
: People with many diseases
If a drug slows down the rate, the other drug will not be
and chronic problems are not likely to be as healthy as
removed as quickly and can build up in the blood, leading
the average person. Their bodies cannot deal with drug
to harmful effects. If a drug speeds up the rate, the other
interactions as well and are more sensitive to their effects.
drug will be removed more quickly from the blood and not
2. Taking multiple drugs
: As stated before, the more
enough drug may be left to work as it should.
drugs one is taking, the more likely it is that a druginteraction may occur.
Finally, if two drugs with opposite effects are taken
3. Being female
: It is not known why, but women do have
together, each will try to cancel out the other’s effects.
a slightly increased rate of drug interactions than men.
One can think of this as a tug-of-war between the two
However, this may be due to the fact that women are
drugs. An example would be using a blood pressure-
more likely to report drug-related problems.
lowering medication with another medication that has a
4. Having a previous drug interaction
: People who have
side effect of raising blood pressure. The end result of
had a previous drug interaction are at higher risk. The
using both drugs together probably would be continued
previous interaction could have been with the same or
5. Being very young or very old
: These age groups are at
higher risk because their bodies handle drugs in
1. increasing or decreasing drug absorption from the
different ways than other individuals. Newborns
haven’t fully developed the ways their bodies get rid of
2. increasing or decreasing the body’s rate of breaking
drugs. The ability of very old people’s bodies to get rid
of drugs is often impaired as a result of damage by
3. increasing or decreasing the body’s rate of excreting
disease. These age groups often have problems with
4. causing competing actions in the body.
6. Being overweight
: Some drugs like to enter the fat
cells in the body and stay there until they are slowlyremoved. People who have increased stores of fat also
What can drug interactions lead to?
will have larger amounts of these drugs remaining intheir bodies for longer periods than a normal-weight
If a drug interaction does occur, any one of the following
person. The longer the drug stays around, the more
scenarios may happen, depending on the drugs involved:
likely a drug interaction will occur.
1. Additive effects, leading to either beneficial results or
7. Being dehydrated
: There are two reasons why
: It seems odd to think of a drug interaction
dehydrated people are at higher risk. For a drug to
as being beneficial or helpful, but it can be. People with
work in the body, it must get into the bloodstream first.
high blood pressure or diabetes often are on multiple
It also must get into the bloodstream in the right
drugs to treat their condition. Often, these drugs will
amount. If too little drug enters the blood, the drug will
interact to give a greater overall effect than if used alone.
not be effective. If too much drug enters, side effects
Additive effects also can be harmful, such as taking two
and possible toxicity may occur. A dehydrated person
medications that have the side effect of drowsiness. When
has less water in the body. Because there is less water
used together, they may make the person extremely
in the blood, everything in the blood becomes more
sleepy, which may lead to a dangerous situation.
concentrated, including drugs. Concentrated drugs are
2. Lessened effects, leading to drug failure
: Using the
more likely to cause side effects and toxicity. Second, a
example of competing drugs from the section above,
dehydrated person is unable to pump as much blood to
one drug can cancel the helpful effects of another. The
the kidneys and liver as other people because the body
drug that is canceled out will fail to do the job it was
is low on water. The kidneys and liver are responsible
for removing drugs from the blood and ridding the
3. No effect, leading to no changes
: The majority of drug
body of them. A dehydrated person is unable to get rid
interactions are not life-threatening or serious. Most
often, no or only minor effects occur, and we usually
8. Having poor nutrition
: Undernourished people are more
sensitive to the effects of drug interactions and don’thave the nutritional stores to help combat those effects.
9. Having low blood pressure
: A person with low blood
This also is a partial list. Surprisingly, cigarette smoke can
pressure will not be able to pump as much blood to the
interact with many drugs. For this reason, it is important to
kidneys and liver as a person with normal blood
inform your doctor or pharmacist if you smoke.
pressure. Therefore, the body will get rid of drugsmore slowly. High blood pressure also increases therisk because it often damages the kidneys and liver,
What are some over-the-counter
making it harder for them to remove drugs.
(nonprescription) drugs that may have
10. Having congestive heart failure
: This person is at
higher risk for the same reason as the previous one. In
We tend to think of OTC drugs as safe. In addition to
this case, the heart is not pumping hard enough.
pharmacies, these drugs are available in grocery stores and
11. Having liver and/or kidney damage
: These organs are
convenience stores. At this point, you may want to ask
responsible for ridding the body of drugs. Damage to
participants what they think about the safety of these
these organs will slow their ability to perform this
drugs, the packaging information, and how to get informa-
function. Drugs may build up and put these people at a
tion about these kinds of drugs. While it is true these drugs
usually are safe as long as they are used as stated on thepackaging, they can interact with other drugs (both pre-
What are some drugs that can increase
scription and nonprescription) even when used as directed.
The partial list below is meant to give participants an idea
blood levels of other drugs?
of what types of commonly used OTC drugs may interact.
The following list is not complete, but is meant to give you
an idea of some of the most common interacting drugs.
Generic name (Brand name
, if applicable)
Most people don’t consider alcohol a drug, but it is. Beer,
wine, and liquor can interact greatly with a wide variety ofdrugs. The end effect depends on the timing and extent of
It is important to always inform your pharmacist and
the drinking. Drinking large amounts of alcohol over a short
doctor of all OTC medications that you are taking.
period of time (several hours to one day) can decrease
therate at which other drugs are removed from the body.
What are some drinks and food that may
Drinking moderate to large amounts of alcohol chronically
over a long period (months to years) can increase
the rateat which other drugs are removed from the body. It is
At this point, ask the participants if they ever have noticed
important to inform your doctor or pharmacist about alcohol
stickers on some prescription bottles that say, “Take medi-
use so he or she can look for possible drug interactions.
cation on an empty stomach.” This advice is given becausesome foods and beverages can interact with drugs (called
What are some drugs that can decrease
drug-food interactions). They can interact in several ways.
blood levels of other drugs?
First, food and drink can bind up some (but not all) drugsin the gut and prevent them from being absorbed into the
Generic name (Brand name
, if applicable)
blood. To avoid this with drugs known to interact with
food, don’t eat until at least a couple hours after taking the
drug, or vice-versa. Usually, the drug can be taken safely
this way. Certain drugs can also have increased absorption
and effects when taken with food. The second type of
food-drug interaction occurs with certain types of food or
both the drug and food have been absorbed into
What are some tips to remember about
the blood. After absorption, the food can change the rate at
which the body rids itself of the drug, by speeding it up orslowing it down. The food also can cancel out or add to the
• With each visit to the doctor, inform him or her of all the
effects of the drug. This second type of interaction is similar
medications (including prescription drugs, OTC drugs,
to the drug-drug interactions discussed earlier. Because
home remedies, and herbal medicines) that you are taking.
this type of interaction occurs after both the drug and food
• Get all prescriptions filled at the same pharmacy.
pass into the blood, it cannot be avoided by taking them at
• Read the drug labels very carefully.
different times. To avoid this type of interaction, it is
• Read directions, warnings, and interaction precautions
usually recommended that the specific type of food or
drink not be taken. Below are some examples of types of
• Take only drugs prescribed for you.
food or drink that may interact with drugs.
• Have your medications thoroughly reviewed by your
Can bind up some drugs in the gut. An example
• Know what to do if you have new symptoms or side
of such a drug is Sumycin® (Tetracycline), which
effects. Know whom to contact and how to reach them.
• Take medicine with a full glass of water.
• Grapefruit juice:
Can slow down the rate at which other
• Don’t stir medicine into your food or take capsules apart
drugs are removed from the body. An example is
• Don’t take vitamin pills at the same time you take
• Vitamins and minerals:
Different ones can bind drugs in
medication without checking first with your doctor
the gut, can cancel out drug effects, or can add to drug
effects. An example is vitamin K and Coumadin®
• Don’t mix medicine into hot drinks.
(Warfarin), a blood thinner. Vitamin K will promote
• Never take medicine with alcoholic drinks.
formation of substances that thicken the blood, which
• Don’t stop taking a drug without checking with
is the opposite effect of the drug Warfarin.
• High-fat meals:
Can increase absorption of some drugs
• Don’t keep old or expired medicines in your medicine
and decrease the absorption of others.
• Don’t be afraid to ask questions
. This is the most
important tip of all and cannot be stressed enough!
Where can one get more information
about drug interactions?
Ask participants where they get their drug information.
Any of the following are good places to get information
Anastasio, G.D., Cornell, K.O., Menscer, D. “Drug
about drugs, including drug interactions.
interactions: Keeping it straight.” American FamilyPhysician
Most accessible. Also, pharmacists have the
Cerrato, P.L. “Vitamins and minerals.” RN
greatest knowledge about interactions.
A good source, but often not available and not as
Drake, A.C., Romano, E. “How to protect your older
For prescription drugs:
Look at the label and any
Haddad, A.R., O’Brien, D. “Counseling patients on drug-
accompanying information, such as brochures or fact
food intractions.” US Pharmacist
Lee, M. “Drugs and the elderly: Do you know the risks?”
For over-the-counter drugs:
Look at “warnings” or
American Journal of Nursing
“drug interaction precaution” section on label. It often
Stein, B.E. “Avoiding drug reactions: Seven steps to writing
will say which drugs or foods may interact with the
safe prescriptions.” Geriatrics
product or which drugs or foods to avoid.
Listed below are some examples
of drug information books written for the public.
1. The Complete Drug Reference
, published by
Consumer Reports. For more information, call
Trade or brand names are mentioned only for educational purposes.
The West Virginia University Extension Service intends no endorsement
2. The USP Guide to Medicines
, published by Avon
nor implies discrimination to the exclusion of other products that also
Books. For more information, call (800) 238-0658.
3. What Do I Take? A Consumer Guide to
Programs and activities offered by the West Virginia University.
, published by the American
Extension Service are available to all persons without regard to race,color, sex, disability, religion, age, veteran status, sexual orientation or
Pharmaceutical Association. For more information,
national origin. Issued in furtherance of Cooperative Extension work,
Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture. Director, Cooperative Extension Service,West Virginia University.
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