Two types of drug-resistant hepatitis B viral strains emerging alternately and their susceptibility to combination therapy with entecavir and adefovir.

The most serious problem of nucleoside/nucleotide analogue therapy for hepatitis B virus (HBV) infection is the emergence of drug-resistant mutant virus. Here, we describe a patient with chronic hepatitis B infection with a complex drug-resistant mutant virus during sequential therapy with lamivudine (3TC), entecavir (ETV) and adefovir dipivoxil (ADV). The patient was a 52-year-old male with positive hepatitis B e antigen and high HBV DNA (>7.6 log(10) copies/ml). Initial 3TC monotherapy offered little benefit and 3TC resistance was established by the virus with rtA181T and not rtM204V/I. HBV DNA was reduced slightly by replacement with ETV monotherapy and was followed by virological breakthrough. At that time, rtA181T was undetectable and the virus with rtM204V and rtL180M became predominant. ETV resistance was established by an additional rtS202G mutation. Efficacy of subsequent combination therapy with ADV and 3TC was limited because of reappearance of the virus with rtA181T, which might confer cross-resistance to 3TC and ADV. Final combination therapy with ETV and ADV reduced HBV DNA to 3.7 log(10) copies/ml for 5 months, which was the most effective therapy for this patient. Thus, two kinds of mutant viruses (rtM204V-related and rtA181T-related) appeared alternately in this patient. Combination therapy with ETV and ADV might have been effective because these drugs share therapeutic roles, that is, ETV affects the rtA181T-related virus and ADV affects the rtM204V-related virus. This is the first report suggesting clinical significance of combination therapy with ETV and ADV for controlling replication of the complex drug-resistant mutant HBV.