The Body PRO Covers: The 8th Conference on Retroviruses and Opportunistic Infections

Drug-Drug Interactions

February 7, 2001

  • Garlic Supplements Decrease Saquinavir Plasma Concentrations (Poster 743)
    Authored by Authored by S. C. Piscitelli, A. H. Burstein, N. Welden, K. Gallicano, and J. Falloon
    View the original abstract

Many HIV-infected patients take alternative medicines with their anti-HIV medicines. These medicines can have significant interactions with antiretroviral medications and should be used with extreme caution. A couple of years ago the case of St. John's Wort was published. This herbal drug is used because of its mild anti-depressant properties. The problem is that it interacts with indinavir and decreases its efficacy thus predisposing to viral failure. The list of herbal preparations that interact with the p450 system is long:

  • St. John's Wort

  • Garlic

  • Ginseng

  • Melatonin

  • Milk Thistle (silymarin)

  • Geniposide

  • Skullcap

Dr. Piscitelli of the National Institutes of Health (NIH) has conducted several trials looking at this issue in HIV-positive individuals. In this poster, Piscitelli et al. looked at the interaction of garlic with saquinavir in healthy volunteers. One garlic capsule was administered twice a day and very careful pharmacokinetics studies were performed. The results were dramatic: garlic reduces the levels of saquinavir by 50%. No data was presented about other antiretrovirals, but this study questions the use of these supplements concomitantly with protease inhibitors. The therapeutic implications of this are unknown.

Saquinavir is used almost exclusively in combination with ritonavir, but no data was presented about the three-way interaction. It might be that ritonavir "compensates" for the effects of garlic.

In any case, it is important that both patients and doctors discuss the use of complementary therapies. This is something that it is not frequently done in our clinics. Doctors need to learn to listen and not "judge" about the use of these remedies and the information then should be captured. Patients need to tell their doctors about all the medicines they are taking, and this includes all herbs, vitamins and supplements.

One thing we've learned for this study is that even with something as harmless as garlic, caution is advised.

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