Antiviral efficacy of combination therapy with entecavir and adefovir for entecavir/lamivudine-resistant hepatitis B virus with or without adefovir resistance

There is little clinical information on the management of hepatitis B virus (HBV) that is resistant to multiple drugs including entecavir (ETV). The present retrospective cohort study assessed the antiviral efficacy of ETV/adefovir dipivoxil (ADV) combination therapy for ETV-resistant HBV with prior lamivudine (LAM) resistance, and either with or without previous ADV resistance. The cumulative probability of achieving a virological response (undetectable serum HBV DNA) was compared by Kaplan-Meier analysis and the Breslow method. Seventeen patients with ETV-resistant HBV who were treated with ETV/ADV combination therapy for at least 6 months at a tertiary care center, were included; seven had dual resistance to ETV and LAM [ADV-r(-) group] and 10 had triple resistance to ETV, LAM, and ADV [ADV-r(+) group]. The median follow-up period was 9 months (range, 6-23). A virological response was noted in seven patients after a median of 3 months (range, 3-12) of treatment; five in the ADV-r(-) group and two in the ADV-r(+) group. The cumulative probability of a virological response was significantly higher in the ADV-r(-) group than in the ADV-r(+) group (6 months cumulative probability, 57.1% vs. 11.1%). In conclusion, ETV/ADV combination therapy led to virological responses in five of seven patients with resistance to ETV and LAM, but a significantly poorer response in patients with prior ADV resistance than in those without prior ADV resistance. Therefore, ETV/ADV combination therapy could be a useful therapeutic option for ETV- and LAM-resistant HBV without prior ADV resistance.