Treatment of HBV involves finite administration of pegylated or unpegylated interferon alfa, or indefinite administration of anti-HBV nucleoside/nucleotide analogues. Five such sellckchem analogues are currently available. Lamivudine, a deoxycytidine analogue, was the first nucleoside approved for use in HBV and lamivudine monotherapy remains common despite high rates of treatment-emergent drug resistance [2]. Entecavir is a deoxyguanosine analogue with a high genetic barrier to resistance in treatment-naive patients [3]. However, lamivudine resistance predisposes HBV to subsequent entecavir resistance [4]. Telbivudine is an L-deoxythymidine analogue with superior efficacy to lamivudine [5] but a similar resistance profile [6].

Finally, the nucleotides adefovir and tenofovir are both acyclic mimetics of deoxyadenosine monophosphate which retain activity against lamivudine- and telbivudine-resistant HBV [6]. However, adefovir is associated with dose-dependent nephrotoxicity which restricts its dosing to 10 mg daily [7], at which dose it demonstrates inferior virologic efficacy to the other agents [8]�C[10]. There are also concerns about the long-term safety of tenofovir, which is associated with significant loss of renal function in HIV treatment [11]. HBV viral replication is a key driver for disease progression and is associated with the development of cirrhosis and HCC [12]. The initial goal of treatment is to suppress viral replication; thereafter, sustained (on-treatment) or maintained (off-treatment) suppression of circulating HBV DNA is associated with improved serological responses and long-term outcomes [13], [14].

The emergence of drug-resistant HBV results in breakthrough viremia leading to hepatitis and liver disease progression. To ensure good long-term outcomes, the conservation of HBV DNA suppression is essential. Early virologic response, particularly at Week 24, is associated with better long-term outcomes in chronic HBV, while detectable HBV DNA at Week 24 is associated with a higher incidence of on-therapy drug resistance [14], [15]. This predictive association has lead an international group of experts to propose the so-called ��Roadmap�� concept �C a therapeutic algorithm for the conditional intensification of nucleoside monotherapy based on early virologic response [16]. In the Roadmap, monotherapy is continued if plasma virus is undetectable (HBV DNA <300 copies/mL) at Week 24; while for those with detectable HBV DNA defined Batimastat options exist for either intensification or continued monotherapy. The Roadmap principle is widely accepted in clinical practice [17], but has yet to be prospectively evaluated.