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Co-infection with the two sexually transmitted viruses is relatively common -- for example, one 2006 study found that half of HIV-positive American gay men also carry hepatitis B, which is a major cause of fatal liver disease, including liver cancer and cirrhosis. More than 1.2 million Americans are thought to be infected with hepatitis B.
Baraclude, which was first approved to fight hepatitis B in early 2005, does perform well at keeping hepatitis B at bay. But it could also undermine the potency of combination drug therapies in patients who are also HIV-positive, the new study showed.
"This means that if you are going to go ahead and treat for hepatitis B, you better be screening for HIV, too," said Dr. Michael Horberg, director of HIV/AIDS Policy, Quality Improvement and Research at Kaiser Permanente in Santa Clara, Calif. "You can't just say, 'I need to treat the hepatitis B with entecavir, and they'll be fine,' because we now know that that is not the case," said Horberg, who was not involved with the study.
The new findings were first presented in February at the Conference on Retroviruses and Opportunistic Infections in Los Angeles.
Soon after the findings' initial release, Baraclude's maker, Bristol-Myers Squibb, changed the medication's labeling to warn of the potential for HIV drug resistance. The U.S. Department of Health and Human Services also revised its hepatitis B treatment guidelines to warn against using Baraclude as a stand-alone treatment in patients co-infected with HIV who are not yet treated for the latter virus.
According to experts, the findings are not a huge surprise, since other drugs used to suppress hepatitis B are also known to effect changes in HIV.
"The active site [of drug action] -- a polymerase enzyme -- is similar on HIV and hepatitis B," explained the study's lead author, Dr. Chloe Thio, an associate professor of medicine at Johns Hopkins University School of Medicine in Baltimore.
Her team tracked changes in HIV levels in the blood, as well as blood counts of CD4 T-cells (a marker of HIV's impact on the immune system) in three men co-infected with hepatitis B and HIV. The patients were using Baraclude to treat their hepatitis B but had not yet begun combination drug therapy to help suppress HIV.
Even though these men were not taking any anti-HIV medicine, their levels of the virus began to fall and their CD4 counts began to rise soon after they started on Baraclude, the study found.
"That sounds like it should be a good thing," Thio said. "But, in fact, it's not good, because we know that one-drug therapy against HIV always leads to resistance."
This healthy dip in HIV levels is always temporary when single drugs are used, Thio said. Sooner or later, a mutation will arise that causes the virus to come back even stronger. That mutation makes HIV more resistant -- not just to Baraclude but to other antiretroviral therapies, as well.
It's a familiar scenario, Horberg said. "All consecutive single agents work for a time and will dramatically drop the [HIV] virus," he noted. "But the virus doesn't have enough pressure in these cases to stop it from mutating."
Especially alarming was the fact that one of the patients tested positive for an HIV mutation called M184V. "That's one of the strongest mutations the virus can create," in terms of upping its resistance to AIDS medications, Horberg said.
So, the bottom line is that patients newly diagnosed with hepatitis B must be tested for HIV before any drug therapy is initiated, the experts said.
The danger extends beyond the individual patient, because people with undiagnosed HIV who are being treated with Baraclude might end up passing a much more highly drug-resistant strain of HIV to their partners, the experts warned.
If a patient does prove to carry both viruses, he or she will probably need to start anti-hepatitis B and anti-HIV therapies simultaneously, Horberg said.
"They may not want to go on [combination] HIV therapy early, but if they want to get very effective therapy for their HIV, it's likely that they will need to," he explained.
SOURCES: Chloe Thio, M.D., associate professor, medicine, Johns Hopkins University School of Medicine, Baltimore; Michael Horberg, M.D., director, HIV/AIDS Policy, Quality Improvement and Research, Kaiser Permanente, Santa Clara, Calif.; June 21, 2007, New England Journal of Medicine
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