The antiviral tenofovir (Viread) is considered the most powerful antiviral currently on the market with the lowest rate of drug resistance, even after five years of use.
But tenofovir may have met its match in a patient who had already developed resistance to the antivirals lamivudine (HBV-Epivir), adefovir (Hepsera) and entecavir (Baraclude) before trying tenofovir.
According to a report by Korean researchers published in the April issue of the Journal of Clinical Virology, the 54-year-old man with HBeAg-positive hepatitis B was treated with tenofovir after unsuccessful treatment with lamivudine, followed by entecavir, and then a combination of adefovir and lamivudine.
The man developed various mutations in his HBV that were able to evade these antivirals that target certain areas of the virus to stop replication. When he finally tried tenofovir, the various mutations he had developed were enough to render even tenofovir ineffective.
“Tenofovir resistance may emerge due to multi-site polymerase (multiple) mutations rather than (a) single-site polymerase mutation,” the researchers wrote.