Adefovir dipivoxil (Hepsera) 

This phosphonate nucleoside analog, administered as the oral prodrug, inhibits replication of HBV, including variants resistant to lamivudine. Adefovir treatment of HBeAg-positive or -negative chronic hepatitis B is associated with marked  reductions in HBV DNA levels, aminotransferase normalization in 48% to 72% of patients, and histologic improvements in 53% to 64% at 48 weeks. More prolonged therapy results in higher rates of response; anti-HBeAg seroconversion occurs in 23% by 72 weeks. The antiviral effects of adefovir are similar in lamivudine-susceptible and -resistant HBV infections (MG Peters et al, Gastroenterology 2004; 126:91). Some experts recommend adefovir over lamivudine for long-term treatment of HBeAg-negative or cirrhotic patients because of the high risk of emergence of lamivudine resistance.