Types of Drug Interactions

by Food and Drug Administration (FDA)

(Page 4 of 4)

Communication Needed

The large number of drugs on the market, combined with the common use of multiple medications, makes the risk for drug interactions significant. "Consumers need to tell doctors what they're taking and ask questions, and health professionals could do a better job at trying to get the information they want," says Timothy Tracy, Ph.D., a professor in the school of pharmacy at the University of Minnesota, Twin Cities campus. He says there is a pervasive attitude that the term "medications" only refers to prescription drugs. "So rather than asking patients what medications they take, doctors should make the questions specific: 'Are you taking any over-the-counter medication? Are you taking any herbal treatments or vitamins?'"

At the same time, Tracy suggests that consumers remind doctors of everything they take when they are prescribed a new medication. So a patient might say: "Now remember, I'm also taking birth control pills. Is there a risk of interaction with this new medicine?"

"Consumers also tend to think that just because something can be bought over the counter, it is without risk," Tracy says. In a study published in the April 2003 issue of the American Journal of Obstetrics and Gynecology, Tracy and his colleagues interviewed 578 pregnant women and found that some of them took medications that should not be used in pregnancy.

"We were surprised that close to 15 percent of the women took ibuprofen during pregnancy, including in the third trimester when ibuprofen is contraindicated," Tracy says. Ibuprofen should not be used in the third trimester because it could cause problems to the unborn child or complicate delivery.

Nearly 60 percent of the women in the study received a prescription medication other than prenatal vitamins, and many medications were prescribed by a physician other than the obstetrician. "We found that women taking long-term medication such as psychotropic agents don't always tell the obstetrician," Tracy says.

In a companion study of non-pregnant women, Tracy and his colleagues found that of 567 study participants, 92 percent took prescription medication, more than 96 percent self-medicated with OTC medications, and almost 60 percent used herbal medicine. The researchers found instances where the pain reliever codeine was taken with the antidepressant Paxil (paroxetine), a combination that can lower codeine's effectiveness. Some patients taking central nervous system (CNS) depressants also were taking the herb kava, which also acts as a CNS depressant.

"We discovered several women taking St. John's wort and SSRIs for depression," Tracy says. "They just had no idea of the interaction potential. Clearly, consumers and health professionals need to work together to prevent potential drug interactions."

Types of Drug Interactions

Drugs with other drugs: This includes both prescription and over-the-counter medicines. Tricyclic antidepressants such as Elavil (amitriptyline) and Pamelor (nortriptyline) can interfere with blood pressure-lowering Catapres (clonidine). Taking the antibiotic Cipro (ciprofloxacin) with antacids lowers Cipro's effectiveness. Some antibiotics, such as rifampin, can lower the effectiveness of birth control pills. Sildenafil, the active ingredient in the erectile dysfunction drug Viagra, should not be taken with nitrates for heart treatment because of the potential for dangerously low blood pressure.

Drugs with dietary supplements: This includes herbs and vitamins, which can interact with drug-metabolizing enzymes. St. John's wort is an herb commonly used by people with cancer to improve mood, but research has shown it interferes with the metabolism of irinotecan, a standard chemotherapy treatment. Vitamin K (in dietary supplements or food) produces blood-clotting substances that may reduce the effectiveness of blood-thinning medicines like warfarin.

Drugs with food and beverages: Taking quinolone antibiotics such as ciprofloxacin with food and drinks such as colas, coffee, and chocolate that contain caffeine may cause excitability and nervousness. There can be a potentially fatal increase in blood pressure if food containing tyramine is eaten when taking monoamine oxidase inhibitors, drugs that treat mood disorders. Examples of food with tyramine are cheese and soy sauce. Grapefruit juice should not be taken with certain blood pressure-lowering drugs or cyclosporine for the prevention of organ transplant rejection. Alcohol should not be taken with pain relievers such as Tylenol (acetaminophen) or ibuprofen because of the increased risk of liver damage or stomach bleeding.

Reduce Your Risk

• Always read drug labels carefully.
• Learn about the warnings for all the drugs you take.
• Make sure all of your doctors know about all prescription drugs, over-the-counter (OTC) drugs, and dietary supplements (including herbs) that you take.
• Keep good records of the medications you take and keep a list in your wallet and at home. Tell a family member where you keep the lists.
• Ask your doctor whether there are any foods or beverages you need to avoid when you are prescribed a new medication.
• Mention the medications you are taking to your doctor when you are prescribed a new medication.
• Check with your doctor or pharmacist before taking an OTC drug if you are taking any prescription medication.
• Use one pharmacy for all of your drug needs.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.