Don't take Ginkgo biloba with efavirenz

The herbal remedy Ginkgo biloba should not be taken with the anti-HIV drug efavirenz, Dutch investigators warn in the June 1^st edition of AIDS. They report the case of an individual whose viral load became detectable, with the development of drug resistance, because Ginkgo biloba interacted with efavirenz.

Efavirenz (Sustiva, also in the combination pill Atripla) is one of the mainstays of first-line HIV treatment. It has a powerful anti-HIV effect, is easy to take, has a long half-life, and generally only causes mild side-effects.

The body metabolises efavirenz using the P450 pathway in the liver. Other medicines, herbal remedies and recreational drugs are also processed using this mechanism, meaning that they can interact with efavirenz.

Such an interaction occurred in a 47-year-old HIV-positive patient in Amsterdam, leading to the virological failure of his HIV treatment.

The patient was fully adherent to his antiretroviral therapy and reported never missing a dose. His treatment consisted of efavirenz combined with FTC (emtricitabine) and tenofovir (Viread). The patient started therapy with this combination in 2005.

In late 2007, he experienced virological failure with the K103N and M184V resistance mutations emerging.

To try and identify the cause of this treatment failure, his doctors questioned him about the use of other medications and drugs. It became clear that the only product the individual had been taking was Ginkgo biloba.

Using stored samples from the two years of efavirenz treatment, the investigators checked concentrations of the drug in the patient’s blood.

Concentrations of efavirenz in his blood declined from a peak of 1.26mg/l (well within the drug’s therapeutic range) in late 2006 when the patient’s viral load was undetectable, to a non-therapeutic 0.48mg/l in February 2008. By this time the patient’s viral load was 1780 copies/ml.

Ginkgo biloba is a widely-used herbal remedy that is thought to have beneficial effects on concentration, memory, dementia and depression. Of note, efavirenz can cause side-effects such as poor concentration and depression. Ginkgo biloba's chemical composition means that, like efavirenz, it is metabolised using the P450 pathway. It is already known that Ginkgo biloba interacts with other drugs processed by the body in this way, such as warfarin, aspirin and ibuprofen.

“We conclude”, write the investigators, “that an intake of Ginkgo biloba extract can decrease human plasma efavirenz levels, may result in virological failure and should be discouraged”.