Fact Sheet Number 419
- WHAT ARE DRUG INTERACTIONS?
- HOW DOES THE BODY PROCESS DRUGS?
- HOW DO DRUGS INTERACT?
- WHY DOES FOOD MATTER?
- WHAT DRUGS CAUSE THE MOST INTERACTIONS?
- WHAT OTHER DRUGS NEED SPECIAL ATTENTION?
- WHAT ABOUT HERBAL PRODUCTS?
- THE BOTTOM LINE
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PrintINTERACTIONS?
The amount of a prescription medication needs to be
high enough to help fight a specific disease, and low enough to
avoid causing too many side effects. Other medications, non-prescription
(over-the-counter) drugs or recreational drugs, herbal products
or even food sometimes cause large changes in the amount of a
medication in your bloodstream. An overdose can cause serious
side effects. An under-dose can mean that the medication will
not work.
BODY PROCESS DRUGS?
Our body recognizes drugs as “foreign substances.” It
removes them, usually in urine or in bowel movements. Many drugs
are removed unchanged by the kidneys. They leave the body in urine.
Other drugs have to be processed by the liver. Chemicals in the
liver (enzymes) change drug molecules. Then they are eliminated
in urine or in bowel movements.
When you take a pill, the drug goes from the stomach into the
intestine. Then it goes to the liver before it is circulated to
the rest of the body. If the drug is easily broken down by the
liver then very little of the drug reaches the body.
INTERACT?
A few drugs slow down the kidneys. This increases the blood levels
of substances that are normally removed by the kidneys.
The most common drug interactions involve the liver. Several
drugs can slow down or speed up the action of liver enzymes. This
can cause big changes in the blood levels of other drugs that
are broken down by the same enzyme.
MATTER?
Any pills that you take go through the stomach. Most drugs are
absorbed faster if the stomach is empty. For some medications,
this is a good thing, but it can also cause more side effects.
Some medications need to be taken with food so that they are broken
down more slowly or to reduce their side effects. Other medications
are taken with fatty foods because they dissolve in fat and are
absorbed better.
Stomach acid breaks down some drugs, including ddI (didanosine,
Videx®). ddI tablets include an antacid buffer that protects
the drug from stomach acid. The buffer, however, interferes with
the absorption of indinavir (Crixivan®), so these drugs should
not be taken at the same time. Newer versions of the drugs should
be easier to take.
THE MOST INTERACTIONS?
Protease inhibitors and non-nucleoside reverse transcriptase inhibitors
are processed by the liver and cause many drug interactions. Everyone
taking anti-HIV drugs needs to be very careful about drug interactions.
Some other types of drugs that are likely to cause interactions
include:
- Antifungal drugs with names that end in “-azole”
- Some antibiotics (names end in “-mycin”)
- The antacid cimetidine (Tagamet®)
- Some drugs that prevent convulsions, including Dilantin®
and Tegretol®.
NOTE: This is not a complete list. Other drugs may also
cause interactions.
DRUGS NEED SPECIAL ATTENTION?
With some drugs, just a little too much in the bloodstream can
cause a dangerous overdose, and if the amount is just a little
too low, the drug might not work. This is called having a “narrow
therapeutic index”. If you are taking this type of drug,
any interactions could be dangerous or possibly fatal.
Drugs with a narrow therapeutic index include:
- Some antihistamines, including Seldane® and Hismanal®
- Drugs to control heart rhythm
- Some pain killers derived from opium
- Propulsid®, which increases bowel activity
- Some sedatives, including Versed® and Halcion®
- Drugs to thin the blood, including Coumadin®
Other drugs to watch out for include recreational drugs.
There are no careful studies of interactions with recreational
drugs, but there have been reports of overdoses and death caused
by taking recreational drugs while taking anti-HIV drugs. A web
site with more information is Party Smarty Marty’s HIV/Recreational
Drugs Interactions at http://www.hafci.org/drugs/
Women taking birth control pills should talk to their
doctor about drug interactions. Some anti-HIV drugs can lower
the levels of these drugs. This could result in an unwanted pregnancy.
WHAT ABOUT HERBAL PRODUCTS?
There has been very little research on interactions between
herbal products and medications. Recent studies have shown that
St. John’s Wort and garlic can both reduce blood levels of anti-HIV
drugs. See fact sheet #729 for
more information on St. John’s Wort.
Garlic supplements, or possibly large amounts of garlic in food,
might cause problems for someone using the protease inhibitors
saquinavir, nelfinavir, indinavir, or amprenavir as the only protease
inhibitor in their regimen.
Many drugs to treat HIV can interact with other medications, drugs,
or herbal products. These interactions can lead to serious or
fatal overdoses of some drugs, or can drop drug levels too low
to do any good. You and your physician should carefully
review the information that comes with each medication (the “package
insert”). Ask for this information for each drug that you
are taking. Also, be sure that a doctor reviews ALL medications,
drugs and herbs you are taking.
Revised October 18, 2002
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New Mexico AIDS Education and Training Center
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