PARIS, Aug 3, 2008 (AFP) - A drug used to fight tuberculosis also hampers the effectiveness of an HIV treatment widely used in Africa, the world's worst AIDS-hit region, a study published on Sunday said.
The antibiotic rifampicin reduces concentrations in the blood of nevirapine, a low-cost agent that is part of the frontline therapy against HIV in poor countries, especially Africa.
The study was presented ahead of the start of the 17th International AIDS Conference, which runs in Mexico City until Friday.
The evidence comes from a study, unfolding in South Africa between 2001 and 2006, among 2,035 individuals who began their treatment with efavirenz, 1,074 of whom had TB, and 1,935 others who initiated with nevaripine, of whom 209 also had TB.
In the nevaripine group, 16.3 percent patients with TB were nearly twice as likely to have elevated levels of HIV in their blood at a six-month follow-up check compared to only 8.3 percent among those without TB.
They were also twice as likely to develop treatment failure faster than patients who did not have TB.
However, a large majority -- 80 percent -- of TB patients using nevirapine also succeeded in suppressing the virus at an 18-month checkup.
The findings are of high importance for sub-Saharan Africa, which is home to two-thirds of the 33 million people infected by the human immunodeficiency virus (HIV).
Around the world, an estimated one-third of the persons living with HIV are coinfected with TB.
For reasons that are poorly understood, coinfection can cause a lightning-fast decline in health, especially if the TB strain is resistant to frontline antibiotics. The death rate among cases of co-infection is five times higher than for tuberculosis alone.
The JAMA study, led by Andrew Boulle of the University of Cape Town, South Africa, said it was unclear why rifampicin had such an impact on nevaripine.
One possible reason could be a shared toxicity. Another could be a drug interaction, caused by rifampicin, when the patient started to receive early doses of the antiretroviral.
Anti-HIV drugs suppress the virus but do not eradicate it completely. If the drugs are halted, the AIDS rebounds.
The study appears in next Wednesday's issue of the Journal of the American Medical Association (JAMA).
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