Myopathy and neuropathy associated with nucleos(t)ide analog therapy for hepatitis B

Treatment of HBeAg-positive chronic hepatitis B with nucleos(t)ide analogues

HBeAg seropositivity is a marker for active viral replication. In the natural history of chronic hepatitis B infection, HBeAg marks the first two of the four phases, namely the immune tolerant phase and the immune clearance phase, and is associated with highly replicative activity of the hepatitis B virus (HBV). Most HBV consensus reports and guidelines recommend antiviral therapy if the immune clearance phase is prolonged and if there is evidence of significant necroinflammation and fibrosis. Two main types of antiviral agents have been approved for treating patients in the immune clearance phase: interferon and nucleos(t)ide analogues (NUCs). The endpoints of therapy are viral suppression with HBeAg seroconversion, undetectable serum HBV DNA, normalization of serum alanine transaminase and improvement in the histological necroinflammatory and fibrosis scores. The ultimate goal of therapy is to obtain clinical benefit for the patient by reducing complications including hepatocellular carcinoma (HCC). The choice between interferon-based immune modulators or NUCs that target the HBV DNA polymerase must be carefully weighed on an individual basis. Therapy with NUCs is often preferred by doctors and patients because it is easy to administer, with predictable efficacy and minimal side-effects. In specific patient subgroups such as those with decompensated disease, poor predictors of response or lack of response to interferon-based therapy and/or significant comorbidities that cannot tolerate interferon-induced side effects, NUCs therapy is the obvious choice. Entecavir and tenofovir are the treatments of choice because their efficacy and safety profile are better than lamivudine, adefovir and telbivudine. More importantly, there is a minimal risk of drug resistance during long-term therapy with these agents.

A comparison of 48-week treatment efficacy between clevudine and entecavir in treatment-naïve patients with chronic hepatitis B

PURPOSE

Clevudine and entecavir are currently available in Korea as antiviral drugs against chronic hepatitis B (CHB). We aimed to compare the efficacy of clevudine and entecavir therapy.

METHODS

Treatment-naïve CHB patients who received 30 mg of clevudine or 0.5 mg of entecavir a day were analyzed. Mean reduction of hepatitis B virus (HBV) DNA levels, complete virological response (cVR, undetectable HBV DNA by real-time PCR), biochemical response (recovery to normal ALT level), and hepatitis B e antigen (HBeAg) seroconversion rate at the 48th week of treatment were assessed.

RESULTS

A number of 59 patients in clevudine group and 61 patients in entecavir group were included. Mean HBV DNA reductions from baseline were similar in the clevudine and entecavir groups, -6.4 versus -6.8 log(10) copies/mL in HBeAg-positive (p = 0.417) and -6.9 versus -7.0 log(10) copies/mL in HBeAg-negative patients (p = 0.640). The proportion of patients who achieved cVR was not different between the two groups, 53 versus 55% in HBeAg-positive (p = 1.000) and 100 versus 95% in HBeAg-negative patients (p = 0.452). Biochemical response rates and HBeAg seroconversion rates were also similar in both the groups. Two (3.4%) patients in clevudine group showed virologic breakthrough with rtM204I mutation using direct sequencing analysis. Clinical myopathy occurred in two (3.4%) patients in clevudine group.

CONCLUSION

Mean reduction of viral loads was similar between clevudine and entecavir groups during 48 weeks. However, virologic breakthrough and significant myopathy were noted only in clevudine-treated patients. Therefore, more attention should be paid to patients receiving clevudine.

Update on new antivirals under development for the treatment of double-stranded DNA virus infections

All the currently available antiviral agents used in the treatment of double-stranded (ds) DNA viruses, with the exception of interferon-α, inhibit the same target, the viral DNA polymerase. With increasing reports of the development of resistance of herpes simplex virus (HSV), cytomegalovirus (CMV), and hepatitis B virus (HBV) to some of these drugs, new antiviral agents are needed to treat these infections. Additionally, no drugs have been approved to treat several DNA virus infections, including those caused by adenovirus, smallpox, molluscum contagiosum, and BK virus. We report the status of 10 new antiviral drugs for the treatment of dsDNA viruses. CMX-001 has broad activity against dsDNA viruses; 3 helicase-primase inhibitors, maribavir, and FV-100 have activity against certain herpesviruses; ST-246 inhibits poxviruses; GS-9191 inhibits papillomaviruses; and clevudine and emtricitabine are active against HBV. Most of these drugs have completed at least phase I trials in humans, and many are in additional clinical trials.

New pharmacologic therapies in chronic hepatitis B

Approximately 350 million persons worldwide are chronically infected with hepatitis B, which can result in cirrhosis, liver failure, and hepatocellular carcinoma. Currently, 2 interferons and 5 nucleos(t)ide analogues have been approved for the treatment of chronic hepatitis B (CHB). This article discusses the mechanisms of action, pharmacokinetics, optimal dose, clinical efficacy, and side effects of medications used for the treatment of CHB.

Discovery and development of anti-HBV agents and their resistance

Hepatitis B virus (HBV) infection is a prime cause of liver diseases such as hepatitis, cirrhosis and hepatocellular carcinoma. The current drugs clinically available are nucleot(s)ide analogues that inhibit viral reverse transcriptase activity. Most drugs of this class are reported to have viral resistance with breakthrough. Recent advances in methods for in silico virtual screening of chemical libraries, together with a better understanding of the resistance mechanisms of existing drugs have expedited the discovery and development of novel anti-viral drugs. This review summarizes the current status of knowledge about and viral resistance of HBV drugs, approaches for the development of novel drugs as well as new viral and host targets for future drugs.

Durability of peginterferon alfa-2b treatment at 5 years in patients with hepatitis B e antigen-positive chronic hepatitis B

Approximately 30%-40% of patients with hepatitis B e antigen (HBeAg)-positive chronic hepatitis B treated with peginterferon and/or lamivudine achieve HBeAg seroconversion 6 months after the end of treatment. The durability and long-term effect of treatment are unknown. In this study, 85 HBeAg-positive patients who received peginterferon alfa-2b 1.5 microg/kg/week for 32 weeks and lamivudine 100 mg/day for 52 or 104 weeks were prospectively followed for 6.1 +/- 1.7 years posttreatment. Twenty-five (29%) patients had virologic response (HBeAg seroconversion and HBV DNA <10,000 copies/mL) at 5 years. The rate of HBeAg seroconversion rose progressively from 37% at the end of treatment to 60% at 5 years. Twenty-seven (32%) and 11 (13%) patients had undetectable HBV DNA (<100 copies/mL) at the end of peginterferon treatment and at 5 years, respectively. Two (2.4%) patients achieved hepatitis B surface antigen (HBsAg) seroclearance at 2.6 and 84 months posttreatment. Among virologic responders at the end of treatment, 82% and 57% and sustained HBeAg seroconversion and virologic response at 5 years. End-of-treatment serum quantitative HBsAg was significantly lower in patients with sustained virologic response at 5 years (median 1,431 IU/mL versus 2,689 IU/mL [P = 0.041]). At the last follow-up, the liver stiffness measurement by transient elastography was 5.8 +/- 2.7 kPa. Only two patients had liver stiffness suggestive of advanced fibrosis. Week 16 HBV DNA, end-of-treatment HBeAg seroconversion, and undetectable HBV DNA were independent factors associated with virologic response at 5 years. The duration of concomitant lamivudine treatment had no impact on any long-term response.

CONCLUSION

Peginterferon has high durability in HBeAg-positive chronic hepatitis B patients with end-of-treatment virologic response.

PSI-7851, a pronucleotide of beta-D-2'-deoxy-2'-fluoro-2'-C-methyluridine monophosphate, is a potent and pan-genotype inhibitor of hepatitis C virus replication

The hepatitis C virus (HCV) NS5B RNA polymerase facilitates the RNA synthesis step during the HCV replication cycle. Nucleoside analogs targeting the NS5B provide an attractive approach to treating HCV infections because of their high barrier to resistance and pan-genotype activity. PSI-7851, a pronucleotide of beta-D-2'-deoxy-2'-fluoro-2'-C-methyluridine-5'-monophosphate, is a highly active nucleotide analog inhibitor of HCV for which a phase 1b multiple ascending dose study of genotype 1-infected individuals was recently completed (M. Rodriguez-Torres, E. Lawitz, S. Flach, J. M. Denning, E. Albanis, W. T. Symonds, and M. M. Berry, Abstr. 60th Annu. Meet. Am. Assoc. Study Liver Dis., abstr. LB17, 2009). The studies described here characterize the in vitro antiviral activity and cytotoxicity profile of PSI-7851. The 50% effective concentration for PSI-7851 against the genotype 1b replicon was determined to be 0.075+/-0.050 microM (mean+/-standard deviation). PSI-7851 was similarly effective against replicons derived from genotypes 1a, 1b, and 2a and the genotype 1a and 2a infectious virus systems. The active triphosphate, PSI-7409, inhibited recombinant NS5B polymerases from genotypes 1 to 4 with comparable 50% inhibitory concentrations. PSI-7851 is a specific HCV inhibitor, as it lacks antiviral activity against other closely related and unrelated viruses. PSI-7409 also lacked any significant activity against cellular DNA and RNA polymerases. No cytotoxicity, mitochondrial toxicity, or bone marrow toxicity was associated with PSI-7851 at the highest concentration tested (100 microM). Cross-resistance studies using replicon mutants conferring resistance to modified nucleoside analogs showed that PSI-7851 was less active against the S282T replicon mutant, whereas cells expressing a replicon containing the S96T/N142T mutation remained fully susceptible to PSI-7851. Clearance studies using replicon cells demonstrated that PSI-7851 was able to clear cells of HCV replicon RNA and prevent viral rebound.

Chronic hepatitis B: whom to treat and for how long? Propositions, challenges, and future directions

Recent guidelines of the American Association for the Study of Liver Diseases, the European Association for the Study of the Liver, and the Asian Pacific Association for the Study of the Liver 2008 update of the "Asian-Pacific consensus statement on the management of chronic hepatitis B" offer comprehensive recommendations for the general management of chronic hepatitis B (CHB). These recommendations highlight preferred approaches to the prevention, diagnosis, and treatment of CHB. Nonetheless, the results of recent studies have led to an improved understanding of the disease and a belief that current recommendations on specific therapeutic considerations, including CHB treatment initiation and cessation criteria, particularly in patient populations with special circumstances, can be improved. Twelve experts from the Asia-Pacific region formed the Asia-Pacific Panel Recommendations for the Optimal Management of Chronic Hepatitis B (APPROACH) Working Group to review, challenge, and assess relevant new data and inform future updates of CHB treatment guidelines. The significance of and controversy about reported findings were discussed and debated in an expert meeting of the Working Group in Beijing, China, in November 2008. This review paper attempts to identify areas requiring improved CHB management and provide suggestions for future guideline updates, with special emphasis on treatment initiation and duration.