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Avoiding Drug Interactions

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Drugs with Dietary Supplements continued...

Examples of drug interactions with dietary supplements …

St. John's Wort (Hypericum perforatum): This herb is considered an inducer of liver enzymes, which means it can reduce the concentration of medications in the blood. St. John's Wort can reduce the blood level of medications such as Lanoxin, the cholesterol-lowering drugs Mevacor and Altocor (lovastatin), and the erectile dysfunction drug Viagra (sildenafil).

Vitamin E: Taking vitamin E with a blood-thinning medication such as Coumadin can increase anti-clotting activity and may cause an increased risk of bleeding.

Ginseng: This herb can interfere with the bleeding effects of Coumadin. In addition, ginseng can enhance the bleeding effects of heparin, aspirin, and nonsteroidal anti-inflammatory drugs such as ibuprofen, naproxen, and ketoprofen. Combining ginseng with MAO inhibitors such as Nardil or Parnate may cause headache, trouble sleeping, nervousness, and hyperactivity.

Ginkgo Biloba: High doses of the herb Ginkgo biloba could decrease the effectiveness of anticonvulsant therapy in patients taking the following medications to control seizures: Tegretol, Equetro or Carbatrol (carbamazepine), and Depakote (valproic acid).

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."