Hepatitis B drug creates HIV resistance.

In people infected with both the hepatitis B virus and the AIDS virus HIV, a widely used treatment for hepatitis also causes HIV to develop drug resistance, scientists report.

Chloe Thio of the Johns Hopkins University School of Medicine in Baltimore and her colleagues studied HIV infection in three patients who were taking the drug entecavir to treat hepatitis B, a virus that attacks the liver. The scientists found that entecavir reduced the amount of HIV in all three patients' bloodstreams.

Entecavir combats hepatitis B by inhibiting an enzyme called DNA polymerase, which plays a central role in viral replication. Thio and her team found that the drug also stymies a similar enzyme, RNA reverse transeriptase, that HIV uses to copy itself.

The team then discovered that one of the patients developed a mutated HIV strain known to resist a variety of anti-HIV drugs. To confirm the change, the scientists engineered the mutation into a lab strain of HIV and showed that it resisted two common anti-HIV drugs.

"We need to really be sure that [hepatitis] drugs don't have HIV activity so they don't harm a patient's chances of being able to have an optimal response to HIV therapy in the future, Thio says. Roughly 10 percent of people worldwide with HIV also have hepatitis B.

The case study, reported in the June 21 New England Journal of Medicine, prompted the Food and Drug Administration's Treatment Guideline Panel to revise its label for entecavir, cautioning doctors not to prescribe the drug in a patient with HIV until that person has already started receiving drugs specifically targeting HIV.--C.B.