Dietary Supplements and Serious Drug Interactions

by Food and Drug Administration (FDA)

(Page 3 of 4)

Interactions With Dietary Supplements

The FDA focus has been mainly on drug-drug interactions, but interactions between drugs and dietary supplements are gaining more and more attention. A recent Institute of Medicine report, sponsored by the FDA, estimated that Americans spend close to $16 billion each year on dietary supplements, which includes vitamins, minerals, herbs, and other plant-derived substances. Their widespread use poses health risks because, unlike new drugs, dietary supplements don't generally have to go through clinical testing and FDA approval before they can be marketed.

Under the 1994 Dietary Supplement Health and Education Act, once a dietary supplement is marketed, the FDA is responsible for showing it's unsafe before the agency can take action to restrict its use. The challenge is that some dietary supplements can interact with enzymes that metabolize drugs. The FDA and the American Society of Clinical Pharmacology and Therapeutics discussed the significance of the problem during a workshop on herb-drug interactions in 2002. The National Center for Complementary and Alternative Medicine, part of the National Institutes of Health, coordinates much of the federal research in this area.

The FDA released a public health advisory in 2000 on the risk of drug interactions when St. John's wort is taken with Crixivan (indinavir), a drug used to treat people infected with HIV, the virus that causes AIDS. St. John's wort is an herb commonly taken to ease the symptoms of depression. An NIH study showed the combination of the two lowered concentrations of Crixivan in the blood, thereby lowering the drug's effectiveness. Based on those results, the FDA determined that St. John's wort may decrease blood concentrations of other drugs that are metabolized in a way similar to Crixivan. St. John's wort increases activity of the CYP3A enzyme.

This can also make other drugs less effective. For example, there are reports of bleeding between menstrual periods and pregnancy in people taking St. John's wort with oral contraceptives. There are also reports of hypertension and a potentially fatal condition called serotonin syndrome when St. John's wort is used with selective serotonin reuptake inhibitors (SSRIs) for depression. Examples of drugs that have St. John's wort listed in the labeling as possibly lowering blood levels are Kaletra (lopinavir and ritonavir) for HIV/AIDS treatment, Mifeprex (mifepristone, RU486) for pregnancy termination, Nuvaring (etonogestrel/ethinyl estradiol) for contraception, Gleevec (imatinib) for cancer treatment, and drugs that prevent rejection of organ transplants such as Neoral (cyclosporine), Rapamune (sirolimus), and Prograf (tacrolimus).

Keeping Up With Drug Interactions

In addition to having a good grasp of drugs and their effects, doctors take medication histories, and they consult with other members of their team to guide them in making decisions about drug interactions. They also use concise drug summaries and resources on pharmacological principles. Flockhart has created a Web site that allows health professionals to identify drug interactions by better understanding how the drugs are metabolized and which enzyme in the CYP450 family is involved.

Health professionals also use computer systems with drug-interaction screening software, electronic prescribing, and other technology. Mark Langdorf, M.D., chair of the department of emergency medicine at the University of California, Irvine, says, "In a busy emergency room, you have to quickly find out what a patient is taking and how those drugs could interact with other treatments."

He and his colleagues considered software programs available to emergency physicians a few years ago. "We found two types: one that checked for interactions but didn't write prescriptions, and one that wrote prescriptions but didn't check for interactions," Langdorf says. "None did both." In a chart review, he found that as many as 17 percent of emergency department patients were taking drug combinations that posed potential interactions. His findings prompted him to work with a software company to design a program.

"Rather than writing a prescription and having to wait until it's checked for drug interactions at the pharmacy," Langdorf says, "we wanted to see a standard computer system that identifies significant drug interactions before the prescription is written."

One challenge is that in an attempt to be comprehensive and avoid liability problems, software screening programs for drug interactions tend to flag every possible interaction, even those that aren't significant, says Daniel Malone, Ph.D., associate professor in the College of Pharmacy at the University of Arizona in Tucson. "Previous research has shown that health professionals are overburdened with alerts that aren't meaningful," Malone says. "We want to prevent useless alerts happening when physicians are trying to write a prescription so they don't get frustrated with the technology and abandon it."

In a CDC-sponsored study, Malone and his colleagues developed a list of 25 clinically important drug-drug interactions likely to occur in community and ambulatory settings. Their findings were published in the March-April 2004 issue of the Journal of the American Pharmacists Association.

"It's just not possible for health professionals to memorize or be aware of every drug interaction," Malone says. "The goal then becomes making the system of preventing drug interactions more efficient."

About the Author

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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.