NIH Cautions HIV Patients Against Taking Garlic Supplements

BETHESDA, Md.--Garlic supplements may reduce the efficacy of saquinavir, a pharmaceutical HIV medication, announced researchers from the National Institute of Allergy and Infectious Diseases, a division of the National Institutes of Health (NIH). According to a study published in the online version of Clinical Infectious Diseases (www.journals.uchicago.edu) on Dec. 5, garlic supplements reduced subjects' blood levels of saquinavir by more than half.

Researchers studied the correlation between garlic and saquinavir because protease inhibitors and garlic share the same pathway into the body--a metabolic route known as the CYP450 enzyme system. In addition, garlic is commonly used to lower blood pressure, which makes it a popular alternative therapy for HIV patients. "The popularity of garlic supplements in our clinic population may be related to claims that garlic has anticholesterol activity, because hypercholesterolemia is a common side effect of antiretroviral therapy," the authors wrote.

Researchers evaluated nine HIV-negative volunteers who received saquinavir, a protease-inhibiting drug that has been shown to slow the progression of HIV infection. For the first four days of the study, subjects took saquinavir (Fortovaser, Roche Laboratories) at a dosage of 1,200 mg three times daily with meals. On days five to 25 of the study, subjects received a commercially sourced form of saquinavir, as well as two doses per day of garlic (GarliPure, Maximum Allicin Formula, Natrol). The garlic capsules, tested by Research Triangle Park Laboratories in Raleigh, N.C., contained 4.64 mg/caplet allicin and 11.2 mg/caplet allin--roughly equivalent to two 4-g cloves of garlic per day. Both treatments were discontinued for a 10-day washout period, and saquinavir was administered again on days 36 to 38.

With garlic supplementation, mean saquinavir area under the curve (AUC) decreased by more than half (51 percent), trough levels at eight hours after dosing decreased by just under half (49 percent), and the mean maximum concentrations decreased by 54 percent. After the 10-day washout period, all blood values increased to 60 to 70 percent of their baseline values. However, scientists did not determine the reason garlic was able to reduce blood levels of saquinavir.

"Our study design was unable to define the mechanism for the alterations in saquinavir levels, but the similarity in the magnitude of the decreases suggests that garlic affected the bioavailability of saquinavir rather than its systemic clearance," the authors noted. "Because the AUC for saquinavir did not return to baseline values after the washout period, it seems likely that this effect is not caused by impairment of absorption in the gastrointestinal tract."

Researchers concluded that HIV patients should be cautious with garlic supplements when saquinavir is being used as a sole protease inhibitor. Judith Falloon, M.D., a researcher on the study, noted that usually HIV patients are given a combined drug regimen, and it is unknown at this point how garlic would affect the efficacy of combination therapy. "More research is needed in this area," she said. "But it's clear from this study that any patient using saquinavir as the sole protease inhibitor should avoid using garlic supplements."

"The study needs to be replicated in a larger population," said Mark Blumenthal, executive director of the American Botanical Council (ABC) (www.herbalgram.org) in Austin, Texas. "Also, these were HIV-negative patients so we don't know if this will work the same way on HIV-positive patients. Just as a skeptic would not accept the benefits of an herbal product based on the power of one study, we can only ask for additional validation of this study in future research. It is certainly interesting and of potential concern for HIV patients taking [saquinavir], but the research has to be reconfirmed."

At press time, Natrol was preparing a statement, which will be published at a later date.