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January 14, 2002
BETHESDA, Md.--Garlic supplements may reduce the efficacy ofsaquinavir, a pharmaceutical HIV medication, announced researchers from theNational Institute of Allergy and Infectious Diseases, a division of theNational Institutes of Health (NIH). According to a study published in theonline version of Clinical Infectious Diseases (www.journals.uchicago.edu)on Dec. 5, garlic supplements reduced subjects' blood levels of saquinavir bymore than half.
Researchers studied the correlation between garlic and saquinavir becauseprotease inhibitors and garlic share the same pathway into the body--a metabolicroute known as the CYP450 enzyme system. In addition, garlic is commonly used tolower blood pressure, which makes it a popular alternative therapy for HIVpatients. "The popularity of garlic supplements in our clinic populationmay be related to claims that garlic has anticholesterol activity, becausehypercholesterolemia is a common side effect of antiretroviral therapy,"wrote the authors.
Researchers evaluated nine HIV-negative volunteers who received saquinavir, aprotease-inhibiting drug that has been shown to slow the progression of HIVinfection. For the first four days of the study, subjects took saquinavir (Fortovase,Roche Laboratories) at a dosage of 1,200 mg three times daily with meals. Ondays five to 25 of the study, subjects received a commercially sourced form ofsaquinavir, as well as two doses per day of garlic (GarliPure, Maximum AllicinFormula, Natrol). The garlic capsules, tested by Research Triangle ParkLaboratories in Raleigh, N.C., contained 4.64 mg/caplet allicin and 11.2mg/caplet allin--roughly equivalent to two 4-g cloves of garlic per day. Bothtreatments were discontinued for a 10-day washout period, and saquinavir wasadministered 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 afterdosing decreased by just under half (49 percent), and the mean maximumconcentrations decreased by 54 percent. After the 10-day washout period, allblood values increased to 60 to 70 percent of their baseline values. However,scientists did not determine the reason garlic was able to reduce blood levelsof saquinavir.
"Our study design was unable to define the mechanism for the alterationsin saquinavir levels, but the similarity in the magnitude of the decreases ...suggests that garlic affected the bioavailability of saquinavir rather than itssystemic clearance," noted the authors. "Because the AUC forsaquinavir did not return to baseline values after the washout period, it seemslikely that this effect is not caused by impairment of absorption in thegastrointestinal tract."
Researchers concluded that HIV patients should be cautious with garlicsupplements when saquinavir is being used as the sole protease inhibitor. JudithFalloon, M.D., a researcher on the study, noted that HIV patients are usuallygiven a combined drug regimen, and it is unknown at this point how garlic wouldaffect the efficacy of combination therapy. "More research is needed inthis area," she said. "But it's clear from this study that any patientusing saquinavir as the sole protease inhibitor should avoid using garlicsupplements."
"The study needs to be replicated in a larger population," saidMark Blumenthal, founder and executive director of the American BotanicalCouncil in Austin. "Also, these were HIV-negative patients so we don't knowif this will work the same way on HIV-positive patients. Just as a skeptic wouldnot accept the benefits of an herbal product based on the power of one study, wecan only ask for additional validation of this study in future research. It iscertainly interesting and of potential concern for HIV patients taking [saquinavir],but the research has to be reconfirmed."
This study was challenged by the American Institute of Biosocial and MedicalResearch (AIBMR) in mid-December. AIMBR expressed concern over the publicitythat resulted from the small study. "The recent attention given to anine-subject pharmacokinetic study modeling the effect of garlic on saquinaviramong HIV patients is very disturbing," said Alexander Schauss, Ph.D.,director of natural and medicinal products research at AIBMR. "Saquinaviris not even approved by the FDA in the way it was used in the study."
Schauss also noted that saquinavir is not supported by the AIDS communitybecause of its dosage level, low bioavailability, high cost and significantinteractions with many other medications. "This study hardly warrants awarning to avoid the use of garlic in AIDS patients," Schauss continued."The very reason physicians recommend garlic to their AIDS patients is tocounteract the significant rise in lipid levels (hyperlipidemias) resulting fromtreatment with such antiretroviral drugs as saquinavir."
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