Drug interactions
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## Who warns the patient?

Most people agree that patients need unbiased, accurate information about drugs they are taking. Who is providing that information? Certainly, physicians and pharmacists are, but pharmaceutical firms and a growing number of Internet prescription "services" are also taking a role. How much responsibility for informing consumers should rest with government agencies?

These questions were provoked by a recent report in the New York Times that the antihistamine Hismanal (astemizole) has - finally - been withdrawn from the US market. Astemizole and similar drugs such as terfenadine have potentially lethal interactions with certain drugs and foods. [1] We wondered how patients get information about drug interactions, and used terfenadine as a test case.

We began with a Web search. We couldn't locate a Canadian site for the manufacturer of terfenadine, and on the US site there was no listing for the drug, presumably because it has been withdrawn from the US market. We discovered that a growing number of Internet sites offer mail-order medication, often without a doctor's prescription. We were unable to find one that supplied terfenadine. (But almost all advertised bargain prices - including for sildenafil citrate "starter kits.") These sites do not look like they will provide unbiased, comprehensive information any time soon.

The FDA Web site [2] easily led us to 117 documents for consumers on terfenadine: several discussed side effects, contraindications and interactions with other drugs and food. Health Canada's site, [3] unfortunately, is not easy to use: despite 3 attempts using different strategies we couldn't find a single document related to terfenadine.

We called Health Canada to ask if we had missed something. Was there any information on their Web site on the hazards of terfenadine? No, there wasn't: this is a prescription drug. Apparently Health Canada considers its duty discharged now that terfenadine cannot be obtained over the counter. It is up to physicians and pharmacists to provide information. We were left with the not very reassuring remark that "The patient can always ask questions."

How are patients to know what questions to ask? Among the substances that can interact with terfenadine are the azole antifungals, erythromycin and the other macrolide antibiotics, selective serotonin reuptake inhibitors, HIV protease inhibitors, quinine and grape-fruit juice. Will every pharmacist, and every prescribing physician, remember each item on the list every time?

Then we visited 2 pharmacies and found that terfenadine is dispensed without product information from the manufacturer. In 1995 the FDA launched a program by which 90% of all prescription drugs will have a package insert giving information on side effects and potential drug interactions by the year 2005. With a few exceptions, there is no such requirement in Canada. The pharmacies we checked used commercially available software to generate information sheets for some drugs. Evidently, patient safety has moved into the marketplace, the realm of "value-added" customer service. When will Health Canada follow the FDA's lead in ensuring that consumer information on prescription drugs is comprehensive, reliable, and delivered every time? Health Canada should assume its responsibility to ensure that accurate and unbiased information is provided not only to doctors and pharmacists but also to patients.

## References

1.  1. Rangno R. Terfenadine therapy: Can we justify the risks? CMAJ1997;157(1):37-8.
    
    [FREE Full Text](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6MzoiUERGIjtzOjExOiJqb3VybmFsQ29kZSI7czo0OiJjbWFqIjtzOjU6InJlc2lkIjtzOjg6IjE1Ny8xLzM3IjtzOjQ6ImF0b20iO3M6MjA6Ii9jbWFqLzE2MS8yLzExNy5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30=) 

2.  2. www.fda.gov/cder/drug.htm (accessed 1999 June 29).
    
    

3.  3. www.hc-sc.gc.ca/hpb-dgps/therapeut (accessed 1999 June 29).