St. John's wort undermines protease inhibitor

Results of a study conducted by researchers at the National Institutes of Health Clinical Center show that St. John's wort, an herbal product used to treat depression, could significantly undermine the effectiveness the antiviral drug indinavir, which is often prescribed to treat HIV infection.

"When St. John's wort and the protease inhibitor indinavir are taken together, the levels of indinavir in the blood drop dramatically," explained the study's principal investigator, clinical pharmacokineticist Dr. Stephen Piscitelli of the NIH Clinical Center's Pharmacy Department. "When the body eliminates the antiviral drug too quickly, there can be a loss of therapeutic benefit."

AIDS research clinician Dr. Judith Falloon of the Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, collaborated on the study, which is featured in The Lancet (vol. 355, no. 9203).

"St. John's wort's effects on indinavir concentrations are large enough to be clinically significant," Falloon said. "Patients and healthcare professionals need to be aware of this interaction. Most people taking medications to treat HIV infection should avoid using St. John's wort."

The NIH Clinical Center study, conducted among eight healthy volunteers, first measured the amount in the body of the drug indinavir when taken alone. Next, study participants were given only St. John's wort for two weeks. Finally, indinavir and St. John's wort were given together.

"The results were dramatically conclusive," Piscitelli said. "All the participants showed a marked drop in blood levels of indinavir after taking St. John's wort. The drop ranged from 49% to 99%."

Added Piscitelli, "Many people think that herbal products like St. John's wort are safe, but there can be dangerous interactions when taken with other medications prescribed to treat medical conditions. This study demonstrates how dangerous that interaction can be and how important it is for patients to keep their physician and pharmacist informed about any use of herbal products." PR