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Avoiding Drug Interactions

Drugs with Other Drugs

Two out of every three patients who visit a doctor leave with at least one prescription for medication, according to a 2007 report on medication safety issued by the Institute for Safe Medication Practices. Close to 40 percent of the U.S. population receive prescriptions for four or more medications. And the rate of adverse drug reactions increases dramatically after a patient is on four or more medications.

Drug-drug interactions have led to adverse events and withdrawals of drugs from the market, according to an article on drug interactions co-authored by Shiew-Mei Huang, Ph.D., deputy director of FDA's Office of Clinical Pharmacology. The paper was published in the June 2008 issue of the Journal of Clinical Pharmacology.

However, market withdrawal of a drug is a fairly drastic measure. More often, FDA will issue an alert warning the public and health care providers about risks as the result of drug interactions.

Examples of drug interactions with other drugs …

Cordarone (amiodarone): FDA issued an alert in August 2008, warning patients about taking Cordarone to correct abnormal rhythms of the heart and the cholesterol-lowering drug Zocor (Simvastatin). Patients taking Zocor in doses higher than 20 mg while also taking Cordarone run the risk of developing a rare condition of muscle injury called rhabdomyolysis, which can lead to kidney failure or death. "Cordarone also can inhibit or reduce the effect of the blood thinner Coumadin (warfarin)," said Huang. "So if you're using Cordarone, you may need to reduce the amount of Coumadin you're taking."

Lanoxin (digoxin): "Lanoxin has a narrow therapeutic range. So other drugs, such as Norvir (ritonvair), can elevate the level of Lanoxin," says Huang. "And an increased level of Lanoxin can cause irregular heart rhythms." Norvir is a protease inhibitor used to treat HIV, the virus that causes AIDS.

Antihistamines: Over-the-counter (OTC) antihistamines are drugs that temporarily relieve a runny nose, or reduce sneezing, itching of the nose or throat, and itchy watery eyes. If you are taking sedatives, tranquilizers, or a prescription drug for high blood pressure or depression, you should check with a doctor or pharmacist before you start using antihistimines. Some antihistamines can increase the depressant effects (such as sleepiness) of a sedative or tranquilizer. The sedating effect of some antihistamines combined with a sedating antidepressant could strongly affect your concentration level. Operating a car or any other machinery could be particularly dangerous if your ability to focus is impaired. Antihistamines taken in conjunction with blood pressure medication may cause a person's blood pressure to increase and may also speed up the heart rate.

Tips to Avoid Problems

There are lots of things you can do to take prescription or over-the-counter (OTC) medications in a safe and responsible manner.

  • Always read drug labels carefully.
  • Learn about the warnings for all the drugs you take.
  • Keep medications in their original containers so that you can easily identify them.
  • Ask your doctor what you need to avoid when you are prescribed a new medication. Ask about food, beverages, dietary supplements, and other drugs.
  • Check with your doctor or pharmacist before taking an OTC drug if you are taking any prescription medications.
  • Use one pharmacy for all of your drug needs.
  • Keep all of your health care professionals informed about everything that you take.
  •  Keep a record of all prescription drugs, OTC drugs, and dietary supplements (including herbs) that you take. Try to keep this list with you at all times, but especially when you go on any medical appointment.

For more information about topics for your health, visit the FDA Consumer Information Center (www.fda.gov/consumer). 

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