Earlier this week Annie Luetkemeyer presented work questioning new FDA guidelines on treating people infected with both HIV and tuberculosis (TB). Here she describes how HIV and TB drugs interact.

Background:

In January, 2012, the U.S. Food and Drug Administration (FDA) issued new guidelines on dosing of an HIV medication used to treat people infected with both HIV and tuberculosis (TB) because of a potential interaction between two of the main drugs used to treat each disease.

The drug rifampin, used for treating TB, can lower levels of the HIV medicine efavirenz, so the FDA recommended that patients who weigh more than 50 kg (110 pounds) and who are taking both medications should get 30 percent larger doses of efavirenz (an increase from 600 mg to 800 mg).

Now, a new analysis by conducted by researchers with the Adult AIDS Clinical Trials Group (ACTG) at the University of California, San Francisco (UCSF) and the San Francisco General Hospital and Trauma Center (SFGH) suggests this recommended dose adjustment may not be necessary, particularly in non-Caucasian populations.

As described in a talk at the XIX International AIDS Conference in Washington, D.C. on Monday, July 23, 2012, the new FDA guidelines were based on several small studies in European TB patients and one in healthy volunteers, indicating a decrease in efavirenz levels with rifampin. The guidelines were also informed by a mathematical model, which showed that increasing efavirenz to 800 mg when given with rifampin would increase levels to those seen on the regular dose of 600 mg.

These data may not apply to patients in African and Asian populations because of genetic differences that lead to higher efavirenz levels—or even in the United States, where more than half the people with TB and HIV co-infections are African American or Asian American.

“To make the recommendation across the board that all patients who weigh more than 50 kg should increase the dose of efavirenz is not supported by our research. Doing so may lead to more drug toxicity without improving the effectiveness of efavirenz in TB patients,” said Annie Luetkemeyer, MD, an assistant professor of medicine at UCSF and an ACTG researcher at SFGH.

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