Combining the herbal therapy gingko biloba with efavirenz (found in Sustiva and Atripla) could result in efavirenz treatment failure, according to a single case report published in the June 1 issue of AIDS and reported by aidsmap.

Experts already recommend that people with HIV tell their providers about all of the medications, vitamins, herbs and supplements they take. This is critical, because when a person starts an HIV regimen it is important to understand the source of any potential side effects and to guard against drug interactions. The drug interaction potential between some herbs and HIV medications, however, is not well understood. This is the case for the herb gingko biloba, which is often used to boost concentration, memory and mood.

In a letter in AIDS, Dirk-Jan Wiegman, MD, from the Onze Lieve Vrouwe Gasthuis in Amsterdam and his colleagues describe the case of an HIV-positive patient who had developed resistance to both efavirenz and emtricitabine (Emtriva) despite excellent treatment adherence. Wiegman’s team asked the man about all other drugs and supplements he’d been taking during his time on efavirenz and found that the only other substance being used was gingko biloba.

Since gingko biloba is metabolized through a similar liver pathway as efavirenz, the P450 enzyme system, and has been found to interact with other drugs, the researchers turned to stored blood samples from the patient to determine how his efavirenz blood levels had been affected over time.

Wiegman and his colleagues found that the man’s efavirenz blood levels had initially been within normal levels when he first began his regimen in 2006, but then dropped significantly after he started taking gingko biloba. While it is not possible to draw firm conclusions from a single case report, the authors suggest: “An intake of [gingko biloba] can decrease [blood levels] of efavirenz, may result in virological failure and should be discouraged.”