US health regulators have issued a warning about Bristol-Myers Squibb’s hepatitis B treatment Baraclude, saying that it can result in resistance to the HIV virus in patients who are suffering from both diseases.

The US Food and Drug Administration, in tandem with B-MS, has issued a letter to healthcare professionals stating that Baraclude (entecavir) is not recommended for HIV/HBV-co-infected patients who are not also receiving highly active antiretroviral therapy due to the potential for the development of HIV resistance.

The agency has also issued a HIV antibody testing should be offered to any potential patient to get Baraclude, Bristol said. The most advanced stage of HIV infection is AIDS, or acquired immunodeficiency virus.

The FDA also noted that it has added a black box warning to the drug’s label which says that before initiating Baraclude therapy, HIV antibody testing should be offered to all patients and that the drug “has not been studied as a treatment for HIV infection and is not recommended for this use”.

B-MS has high hopes for Baraclude which was approved by the FDA in March 2005 and had sales of $59 million in the second quarter, up from $14 million a year earlier. The World Health Organisation notes that of the 2 billion people who have been infected with HBV, more than 350 million have chronic infections. It is most common in sub-Saharan Africa, most of Asia and the Pacific, and worldwide, most cases occur from infected mother to child and from child-to-child contact in household settings. In Europe and North America, however, the people most likely to get HBV are drug users and homosexual men.