Sustained virological and biochemical responses to lamivudine and adefovir dipivoxil combination in a chronic hepatitis B infection despite mutations conferring resistance to both drugs

[Analogs combination therapy in chronic hepatitis B: when and how?]

Hepatitis B virus (HBV) genomic variability is responsible for the complexity of the viral quasi-species and its evolution during the course of infection. The persistence of infected cells promotes the selection of drug-resistant strains. The development of nucleoside analogs without cross-resistance has provided a rationale for combination therapy. De novo combination, with low genetic barrier drugs, prevents the emergence of resistance in the short-term for drugs with a low genetic barrier and improves the control of infection. Long-term studies are needed to determine whether de novo combination is beneficial for analogs with a high genetic barrier as well. The add-on strategy is a standard in case of emergence of resistant mutants. This strategy needs to be implemented as early as possible before the virological breakthrough, especially if the viral suppression is sub-optimal. Clinical trials are mandatory in order to assess whether a) de novo combination is better than an early add-on strategy; and b) whether in case of sub-optimal viral suppression, an early add-on strategy is better in the long-term than a switch to a more potent drug with a high genetic barrier.

Avoiding and managing lamivudine resistance in chronic hepatitis B: current approaches and potential strategies including pegylated interferon

Since its approval for the treatment of chronic hepatitis B in 1998, lamivudine (LAM) has been used extensively throughout the world, because of its relatively low costs and favourable tolerability. However, clinical trials and cohort studies have demonstrated that a high rate of resistance to this drug develops and, as a result, it is no longer included as a first-line therapy in most current treatment guidelines. Nevertheless, because of its low cost, this drug continues to be used in many countries and the pool of patients who have developed resistance to LAM continues to increase. Thus, there is a clear need to develop coherent management strategies to treat such patients as well as limit the emergence of resistance in the first instance. The purpose of this review is to highlight the need to aim for long-term treatment success while limiting the emergence of drug resistance and its consequences for the future. In addition to add-on/switch strategies with other nucleos(t)ide analogs, currently available data suggest that interferon-based therapies, with their potential to induce a sustained response, are worthy of consideration not only for reducing de novo resistance but as an option for the management of those patients in whom drug resistance has already developed.

Assessment of selective real-time PCR for quantitation of lamivudine and adefovir hepatitis B virus-resistant strains and comparison with direct sequencing and line probe assays

A selective real-time PCR (sPCR) assay has been developed to detect the rtM204V/I and rtN236T mutations of hepatitis B virus (HBV) associated with resistance to lamivudine and adefovir. Using mixtures of mutant and wild-type plasmids, this sPCR was able to detect 0.1% of mutated strain in a total plasmid population of 10(5) copies and was more sensitive in detecting resistant strains than the line probe INNO-LiPA-DR-v2 assay and a direct sequencing assay. The comparison of these methods on 20 clinical specimens from treated patients confirmed the plasmid results: the three methods were concordant for the detection of the mutant strains in 72% of the cases and the discrepant results were caused mainly by the sequencing assay's lack of sensitivity. The line probe assay was more sensitive for detecting mutations than sPCR when the viral load was less than 10(4) copies/ml; conversely, the sPCR provided a more sensitive detection when the viral load was greater than 10(4) copies/ml. Although difficult to perform in clinical practice, sPCR appears to be a reliable technique for detecting and quantifying quasi-species resistant to lamivudine (LAM) and adefovir (ADV) and can be useful to gain a better understanding of the natural history of antiviral resistance during the treatment of chronic hepatitis B (CHB).