Adefovir dipivoxil alone or in combination with lamivudine in patients with lamivudine-resistant chronic hepatitis B

Management of Hepatitis B Patients with Antiviral Resistance

Drug resistance is an expected consequence of antiviral therapy for chronic hepatitis B because of the high rate of hepatitis B virus (HBV) replication, the lack of proofreading during reverse transcription of the pregenomic RNA and the low efficacy of available therapies in eliminating covalently closed circular HBV DNA. Mutations involving the YMDD motif of the catalytic domain of HBV reverse transcriptase have been reported in patients who have received lamivudine, emtricitabine and telbivudine. Drug-resistant mutations affecting other regions of HBV polymerase have also been reported, but at much lower rates in patients who have received adefovir dipivoxil or entecavir. Antiviral resistance is initially manifested as virological breakthrough infection. In most patients, this is followed by biochemical breakthrough and, in some patients, hepatitis flares and hepatic decompensation. Monitoring drug resistance may improve the management of patients with antiviral-resistant HBV and can guide the selection of salvage therapy. The optimal management of patients with antiviral-resistant HBV continues to evolve. The ideal approach is to prevent antiviral resistance through judicious use of antiviral therapy and the use of more potent antiviral agents, possibly in combination.

Management of Antiviral Resistance in Patients with Chronic Hepatitis B

A meeting of physicians and scientists involved in the management of chronic hepatitis B (CHB) was held to review current scientific data regarding antiviral resistance in hepatitis B virus (HBV) infection. The goals of the meeting were to describe current treatments for CHB, discuss emerging issues in HBV drug resistance and to delineate patient monitoring, including markers for resistance, during administration of antiviral therapy. The aim of this review article is to provide treating physicians with a framework for the management of CHB in the context of antiviral resistance. Definitions of primary and secondary antiviral treatment failure can be used to aid monitoring and early diagnosis of drug resistance before disease progression occurs as a consequence of viral breakthrough. Primary antiviral treatment failure is defined as failure of a drug to reduce HBV DNA levels by ≥1xlog10 IU/ml within 3 months following initiation of therapy, and secondary antiviral treatment failure as a rebound of HBV replication of ≥1xlog10 IU/ml from nadir in patients with an initial antiviral treatment effect (≥1xlog10 IU/ml decrease in serum HBV DNA). Confirmation of antiviral drug failure can be established by sequencing the HBV DNA polymerase and identifying specific genetic markers of antiviral drug resistance. In addition to virological assays, HBV resistance can be assessed from a clinical perspective including increased serum alanine aminotransferase levels and the development of systemic symptoms or signs of liver failure. Potential strategies to prevent the emergence of resistance and how to manage drug-resistant HBV once it emerges are discussed.

Antiviral therapy: nucleotide and nucleoside analogs

For the management of HBV infection, an increasing number of nucleotide and nucleoside analogs are active against wild-type HBV and some against HBV with YMDD and other compensatory mutations. Table 2 depicts the IC50 and susceptibilities of HBV to various antiviral agents. The dichotomy between in vitro and in vivo susceptibilities to YMDD mutants is due to a change in IC50 between wild-type and mutant virus. Thus a drug may have less activity in vitro but at doses used in vivo show activity against YMDD and other compensatory mutations. Some HBV drugs share activity against HIV, which may be useful in the co-infected patient. Other nucleoside analogs are in various stages of development, including MCC-478 and DAPD. In the future, clinicians will have a plethora of reagents to chose from, and combination therapies may be invoked.

Antiretroviral therapy and HIV/hepatitis B virus coinfection

Among human immunodeficiency virus (HIV)-infected individuals, the prevalence of hepatitis B surface antigen (HBsAg) seropositivity is approximately 10-fold higher than in the general population. HIV/hepatitis B virus (HBV)-coinfected patients have an increased risk of cirrhosis and liver-disease-related death. The strategy and management of anti-HBV therapy in HIV-infected persons must take into consideration both viral infections. Among HIV/HBV-coinfected patients, lamivudine promptly inhibits HBV replication. The emergence of resistance to lamivudine has been documented in HBV strains. Adefovir has been shown to be effective in the treatment of lamivudine-resistant HBV in HIV/HBV-coinfected patients. Tenofovir has recently been shown to have significant activity against both HIV and HBV. HBsAg seropositivity has been identified as an independent predictor of highly active antiretroviral therapy-related hepatotoxicity. However, further research is needed to determine the exact role of HBV and the mechanisms involved in antiretroviral-associated hepatotoxicity in HBV/HIV-coinfected patients.

A treatment algorithm for the management of chronic hepatitis B virus infection in the United States

BACKGROUND AND AIMS

Chronic hepatitis B is an important public health problem worldwide and in the United States. A treatment algorithm for chronic hepatitis B virus (HBV) infection was developed by a panel of US hepatologists based on new developments in the understanding of the virology of HBV, availability of more sensitive molecular diagnostic testing, and advantages and disadvantages of currently approved therapies.

METHODS

This algorithm is based on available evidence, but where data are lacking, the panel relied on clinical experience and consensus expert opinion.

RESULTS

Serum HBV DNA can be detected at levels as low as 100-1000 copies/mL by using molecular assays and should be determined to establish a baseline level before treatment, monitor response to antiviral therapy, and survey for the development of drug resistance. The primary aim of antiviral therapy is durable suppression of serum HBV DNA to the lowest level possible. The threshold level of HBV DNA for determination of candidacy for therapy is >/=10(5) copies/mL for patients with hepatitis B e antigen (HBeAg)-positive chronic hepatitis B. A lower serum HBV DNA threshold is appropriate for patients with HBeAg-negative chronic hepatitis B and those with decompensated cirrhosis, and the panel recommends thresholds of 10(4) copies/mL and 10(3) copies/mL, respectively.

CONCLUSIONS

Interferon alfa-2b, lamivudine, and adefovir dipivoxil are all approved as initial therapy for chronic hepatitis B and have certain advantages and disadvantages. Issues for consideration include efficacy, safety, incidence of resistance, method of administration, and cost. Studies are under way to explore the safety and efficacy of combination therapy, which may prove to be more effective than monotherapy in suppressing viral replication and may decrease or delay the incidence of drug resistance.