Treating hepatitis B patients with the drug entecavir can cause those who are also infected with HIV to become resistant to two of the most important drugs in the anti-HIV arsenal, according to a new report in the New England Journal of Medicine. In findings published June 21, 2007, online in the journal, the researchers reported that a patient infected with both hepatitis B and HIV who was treated with entecavir developed a mutant strain of HIV that is resistant to the antiviral drugs lamivudine and emtricitabine. Entecavir is manufactured by Bristol-Myers Squibb and is marketed under the trade name Baraclude.