Deoxyguanosine kinase (dGK) is reported responsible for the phosphorylation of deoxyadenosine (dA) and deoxyguanosine (dG) in the mitochondrial purine salvage pathway. Antiviral nucleoside analogs known as nucleoside reverse transcriptase inhibitors (NRTIs) must be phosphorylated by host enzymes for the analog to become active. We address the possibility that NRTI purine analogs may be competitive inhibitors of dGK. From a group of such analogs, we demonstrate that entecavir (ETV) competitively inhibited the phosphorylation of dG and dA in rat mitochondria. Mitochondria from the brain, heart, kidney, and liver showed a marked preference for phosphorylation of dG over dA (10-30-fold) and ETV over dA (2.5-4-fold). We found that ETV inhibited the phosphorylation of dG with an IC50 of 15.3 ± 2.2 μM and that ETV and dG were both potent inhibitors of dA phosphorylation with IC50s of 0.034 ± 0.007 and 0.028 ± 0.006 μM, respectively. In addition, the phosphorylation of dG and ETV followed Michaelis-Menten kinetics and each competitively inhibited the phosphorylation of the other. We observed that the kinetics of dA phosphorylation were strikingly different from those of dG phosphorylation, with an exponentially lower affinity for dGK and no effect of dA on dG or ETV phosphorylation. Finally, in an isolated heart perfusion model, we demonstrated that dG, dA, and ETV were phosphorylated and dG phosphorylation was inhibited by ETV. Taken together, these data demonstrate that dGK is inhibited by ETV and that the primary role of dGK is in the phosphorylation of dG rather than dA.

Nucleoside and nucleotide analogues (NAs) have a risk of mitochondrial toxicity and then inducing the increase of lactate. We aim to evaluate the impact of lactate on the effects of NAs therapy in hepatitis B virus-related hepatocellular carcinoma (HCC) patients after curative liver resection.

Five hundred and fifty-seven HBV-related HCC patients were divided into the treatment and control group according to whether they received NAs therapy or not. Perioperative and prognosis data were retrospectively reviewed.

The treatment group had a better overall survival rate (OS) than the control group (P = 0.017). The recurrence-free survival rate (RFS) did not significantly differ between the two groups (P = 0.174). NAs could improve the OS of early stage HCC patients (P = 0.028), as well as the OS of advanced stage HCC patients with low level of lactate in subgroup analysis stratified against the level of lactate (P = 0.037). Advanced stage HCC patients in the treatment group had a higher value of lactate than those in the control group (P = 0.024). Besides, advanced stage HCC patients had a higher value of lactate than early stage HCC patients in the treatment group (P < 0.001), as well as in the control group (P < 0.001).

NAs could improve the long-term outcomes of HBV-related HCC patients after curative liver resection. However, the improvement effect of NAs therapy is counteracted by the adverse effect of elevated lactate in advanced stage HBV-related HCC patients.

Safety profile of nucleos(t)ide analogues is an important issue in view of its widespread use for decades in patients with chronic hepatitis B (CHB).

To review and evaluate the latest evidence on the safety profiles of the six approved nucleoside analogues.

Relevant articles related to nucleoside analogue safety were selected for review following extensive language- and date-unrestricted, electronic searches of the literature.

Nephrotoxicity has been well reported in patients receiving older generations of nucleotide analogues, namely adefovir dipivoxil and tenofovir disoproxil fumarate (TDF). Yet risks of renal failure and renal replacement therapy were similar in patients treated with nucleoside analogues versus nucleotide analogues in real-life setting. Bone toxicity is closely related to nucleoside analogue effect on renal proximal tubular and phosphaturia. Real-life data demonstrated increased risk of hip fracture in patients receiving adefovir but not TDF. The newly approved tenofovir alafenamide (TAF) has improved renal and bone safety profiles compared to TDF. Long-term use of nucleoside analogues eg entecavir does not increase the risk of other cancers. Muscular toxicity may be seen in telbivudine-treated patients so regular monitoring is advised. Peripheral neuropathy and lactic acidosis are rare adverse events. Latest international guidelines support the use of TDF, telbivudine and lamivudine during pregnancy; breastfeeding is not contraindicated during TDF therapy.

Long-term safety profile of nucleoside analogues is now better defined with more data from large real-life cohorts and clinical trials with long-term follow-up. The new nucleotide analogue, TAF is now available with favourable renal and bone safety profiles.

The aim of this study is to evaluate the clinical implications of lactate concentrations in patients with hepatitis B with or without cirrhosis during treatment with nucleos(t)ide analogues.

One hundred and seven consecutive patients with chronic hepatitis B and median age 57 (24-85) years were prospectively included. Lactate concentrations were measured at baseline and at 12, 24, 36, 48, and 60 months following the baseline measurements. Eight (n=8, 7.5%) patients received lamivudine, 38 (n=38, 35.5%) patients received tenofovir, 34 (n=34, 31.8%) patients received entecavir, and 27 (n=27, 25.2%) patients received combined therapy.

None of the patients developed lactic acidosis during follow-up [median: 58 (6-155) months]. Overall, no trends of the lactic acid evolution were observed over time; however, there was a nonsignificant increasing trend in patients with cirrhosis up to 24 months of treatment. This increasing trend was significant in female patients with cirrhosis (P=0.016). The age of the patients, the presence of cirrhosis, and hepatocellular carcinoma were strongly associated with the survival of all patients. In the group of cirrhotic patients, the only independent prognostic factor that was associated with patients' survival was the Child-Pugh class.

None of the patients developed lactic acidosis. There is an indication of an increasing trend of lactic acid levels up to 24 months of therapy in female cirrhotic patients.

Nucleos(t)ide analogues (NUCs) for chronic hepatitis B treatment achieve high rates of viral suppression and are generally well tolerated. Entecavir (ETV) and tenofovir disoproxil fumarate (TDF) are the currently preferred first-line agents. The safety of these agents in clinical practice is particularly relevant since long-term treatment is usually required.

To summarise and critically discuss recent real-world evidence on the safety of treatment with ETV or TDF in hepatitis B virus (HBV)-monoinfected patients.

PubMed and conference proceedings up to 15th June 2015 were searched using the terms ((((Hepatitis_B) OR HBV) AND ((tenofovir) OR entecavir)) AND (((lactic_acidosis) OR bone) OR renal)).

In selected populations included in registration studies, both ETV and TDF were well tolerated with no clinically significant renal toxicity or lactic acidosis. Growing 'real-world' clinical experience with these agents includes some reports of ETV-associated lactic acidosis and TDF-associated renal impairment; however, evidence from cohort studies appears to be conflicting. In the case of ETV-related lactic acidosis, a small number of cases have been reported, all in patients with decompensated cirrhosis. The degree of association between TDF treatment and changes in markers of renal function varies between studies: discrepancies may result from the use of different definitions and cut-offs for reporting renal toxicities, and differences in patient populations.

Pre-treatment and on-treatment monitoring of eGFR and phosphorus, with prompt appropriate dose adjustment or treatment switch can minimise the impact of NUC renal toxicity. Standardisation of measures of renal impairment and identification of early molecular markers remain an unmet need.

Oral nucleoside/ nucleotide analogues (NAs) are currently the mainstay of treatment for patients with chronic hepatitis B virus (HBV) infection. They are generally safe to use. However, since their approval in the last decade and a half, the literature has reported adverse effects associated with the use of NA in HBV patients. A comprehensive review on the drug safety is lacking.

Significant adverse effects associated with NA use in HBV patients including muscle toxicity, peripheral neuropathy, nephrotoxicity and lactic acidosis are discussed. The reported prevalence of each adverse effect, as well as their predictive factors, reversibility and their use in pregnancy and lactating mothers are covered in this review. Novel data regarding reno-protective effect of telbivudine are also discussed.

Use of NA in HBV is generally safe. Uncommon adverse effects can be minimized or detected early if clinicians exercise adequate precautions when using NA for at-risk populations with regular monitoring.

Worldwide, some 240 million people have chronic hepatitis B virus (HBV), with the highest rates of infection in Africa and Asia. Our understanding of the natural history of HBV infection and the potential for therapy of the resultant disease is continuously improving. New data have become available since the previous APASL guidelines for management of HBV infection were published in 2012. The objective of this manuscript is to update the recommendations for the optimal management of chronic HBV infection. The 2015 guidelines were developed by a panel of Asian experts chosen by the APASL. The clinical practice guidelines are based on evidence from existing publications or, if evidence was unavailable, on the experts' personal experience and opinion after deliberations. Manuscripts and abstracts of important meetings published through January 2015 have been evaluated. This guideline covers the full spectrum of care of patients infected with hepatitis B, including new terminology, natural history, screening, vaccination, counseling, diagnosis, assessment of the stage of liver disease, the indications, timing, choice and duration of single or combination of antiviral drugs, screening for HCC, management in special situations like childhood, pregnancy, coinfections, renal impairment and pre- and post-liver transplant, and policy guidelines. However, areas of uncertainty still exist, and clinicians, patients, and public health authorities must therefore continue to make choices on the basis of the evolving evidence. The final clinical practice guidelines and recommendations are presented here, along with the relevant background information.

Although there have been reports on telbivudine-induced myopathy and creatine kinase (CK) elevation, few reports focus on its effect on hyperlactatemia in patients with chronic hepatitis B (CHB). Here we reported a case of hyperlactatemia during telbivudine treatment. A 26-year-old Chinese man had been receiving telbivudine for CHB since July 2011, with a CK level of 68 U/L before the antiviral therapy. After 3 months he felt muscular weakness in both upper and lower extremities. A check in the local clinic found his CK level was increased to 222 U/L (upper limit of normal 170 U/L). However, he did not visit his doctor or stop the telbivudine treatment until he felt myalgia throughout his body. By this time his CK level had increased to 4151 U/L. Even after the withdrawal of telbivudine, his myalgia was exacerbated and his CK level was decreased extremely slowly. His constant myolysis developed into hyperlactatemia and he finally recovered after successful venovenous hemodiafiltration. The findings in this patient suggest that telbivudine may lead to high CK levels and hyperlactatemia may occur if telbivudine is not discontinued immediately when CK levels are clearly increased. Moreover, we emphasized that serum CK and lactate levels should be monitored closely during treatment with telbivudine in patients with CHB.

Oral nucleoside/nucleotide analogues (NAs) are the mainstay of therapy for patients with chronic hepatitis B and are generally well tolerated. Despite this, the safety profile of NAs is of paramount importance since the majority of patients will require long-term treatment. All NAs can potentially affect human DNA polymerase with decrease in mitochondrial DNA, leading to manifestations of mitochondrial toxicity. As a class effect, therefore, NAs can potentially cause extrahepatic conditions, such as myopathy, nephropathy, neuropathy, and lactic acidosis. Indeed, effects on muscles, including myopathy and creatine kinase elevations, have been described with clevudine and telbivudine use. Both adefovir and tenofovir are associated with dose-dependent nephropathy, predominantly affecting the proximal renal tubules. Neuropathy appears to be rare, and most commonly reported in patients receiving combination therapy with telbivudine and interferon. Increased risk of lactic acidosis has also been described for those with impaired liver and renal function taking entecavir. Loss of bone mineral density and hypophosphatemia have been described with the use of NAs, although the overwhelming studies have been with human immunodeficiency virus-infected patients. However, not all extrahepatic effects are detrimental. Recent evidence has suggested a potential renal beneficial effect with the use of telbivudine. The effect of NAs on pregnancy appears to be minimal for all NAs, with telbivudine and tenofovir having a more favorable category B rating. Ongoing pharmacovigilance is essential to identify new and monitor existing extrahepatic effects associated with NA use.

Hepatitis B virus (HBV) is the most important cause of acute liver failure (ALF) in Eastern countries. HBV-related ALF may occur after acute HBV infection (A-ALF) or during acute exacerbation (flare) of chronic HBV infection (C-ALF). C-ALF may occur spontaneously or as a result of the effect of immunosuppression due to chemotherapeutic or immunosuppressive agents. The definition of HBV-related ALF is uncertain, because different diagnostic criteria are used in C-ALF, which may present as acute-on-chronic liver failure. Although the pathogenesis differs in the two subgroups of ALF, the symptoms and biochemical parameters can be similar. High titers of immunoglobulin M hepatitis B core antibody and lower viral loads are frequent in A-ALF as compared with C-ALF. The prognosis of C-ALF is significantly poor as compared with that of A-ALF. In C-ALF, most immunosuppression-mediated reactivation of hepatitis B results in fatality. Many case series or case-control studies have not demonstrated the survival benefit of nucleos(t)ide treatment. This treatment failure is probably related to delayed initiation of nucleos(t)ide treatment and viral suppression. Treatment with nucleos(t)ide analogs should be started immediately and should be continued regardless of subgroups of HBV-related ALF. Liver transplantation is the only treatment option that improves the prognosis of HBV-related ALF. Patients under consideration for transplantation should be given nucleos(t)ide analogs as prophylaxis to reduce the likelihood of post-transplant HBV recurrence.

For patients undergoing liver transplantation (LT) for hepatitis B virus (HBV)-related liver disease, the current standard of care for preventing reinfection of the allograft is nucleoside analogue therapy combined with hepatitis B immune globulin (HBIG). Entecavir has demonstrated high efficacy and a favorable safety profile for chronic hepatitis B (CHB) treatment, but data for patients undergoing HBV-related LT are limited. This study assessed the safety and efficacy of entecavir combined with various HBIG regimens after CHB-related LT. In this phase 3b, single-arm, open-label study, 65 patients undergoing LT for CHB-related liver disease with an HBV DNA load <172 IU/mL at LT received entecavir (1.0 mg daily) for 72 weeks after LT. The primary endpoint was the proportion of evaluable patients (treated for ≥4 weeks) with virological recurrence (HBV DNA level ≥50 IU/mL) through week 72. Concomitant HBIG therapy was received by 64 of the 65 enrolled patients, and 44% of these patients received high-dose HBIG (any HBIG dose in the specified interval ≥10,000 IU). Through week 72, all 61 patients evaluable for the efficacy analysis had undetectable HBV DNA. The Kaplan-Meier estimate of patients without hepatitis B surface antigen (HBsAg) recurrence at week 72 was 0.9655. Two patients experienced a reappearance of HBsAg, but both remained HBV DNA(-) until the last follow-up. The frequency and nature of adverse events were consistent with those expected for this patient population. Serum creatinine increments ≥0.3 mg/dL and ≥0.5 mg/dL occurred in 62% and 39% of the patients, respectively, and all of these patients received calcineurin inhibitor therapy. In conclusion, in this population of patients treated with entecavir after CHB-related LT, entecavir was well tolerated and effective in maintaining viral suppression, even in individuals who experienced a reappearance of HBsAg.

The nucleotide analogue adefovir dipivoxil (ADV) was approved in 2002 for the treatment of chronic infection with hepatitis B virus (HBV), in both hepatitis B e antigen (HBeAg)-positive and -negative patients. ADV 10 mg daily has been associated with improved liver histology, decreased levels of HBV DNA and alanine aminotransferase (ALT), and seroconversion of HBeAg.

This paper reviews the use of ADV as a first-line treatment for chronic hepatitis B and as an add-on therapy in chronic HBV-infected patients with lamivudine resistance. In the years since its launch, clinical resistance to ADV has emerged, and tenofovir and entecavir have shown greater efficacy in reducing viral load.

Many patients who started antiviral therapy with ADV (either as monotherapy or in combination with lamivudine) remain on this agent because they have undetectable viremia, but its future use will probably diminish because of the availability of more potent drugs. ADV is generally well tolerated, though the 10 mg dose is associated with low risk of nephrotoxicity.

Despite a decline in cases of acute hepatitis B and the low hepatitis B virus (HBV) chronicity rates in adults, still some patients progress to HBV-related fulminant liver failure. In this review, we discuss treatment options that may prevent the progression of severe acute hepatitis B to fulminant liver failure and death. In severe acute HBV with prolonged prothrombin time and increased bilirubin, interferon failed to be effective while antiviral treatment, particularly with lamivudine, appears to improve survival (mean survival almost 80%). Outcome without antiviral therapy has remained considerably poor, whereas there is no convincing evidence of amelioration of HBV-targeted immunity. Of note, most patients who died or required transplantation despite lamivudine therapy, were started on lamivudine at advanced stages compared with those survived. This suggests that prompt and timely antiviral therapy is crucial. Owing to the abovementioned results the design of randomized placebo-control trials in the setting of severe acute hepatitis B seems unethical. On the contrary, the design of multicentre double-blind randomized trials to compare the efficacy between lamivudine and entecavir or even tenofovir in acute severe HBV cases is ideally needed, but these studies appear to be very difficult to perform considering that these cases are not frequent and therefore, it is almost impossible to have two arms adequately numerous and homogenous for statistical evaluation. Thus, in the absence of solid evidence based data, the hepatologists could treat their patients with severe acute hepatitis B with lamivudine or the most potent antivirals entecavir or tenofovir.

Hepatitis B virus (HBV) during pregnancy presents unique management challenges. Varying aspects of care must be considered, including the effects of HBV on maternal and fetal health, effects of pregnancy on the course of HBV infection, treatment of HBV during and after pregnancy, and prevention of perinatal infection. Antiretroviral therapy has not been associated with increased risk of birth defects or toxicity, but despite studies designed to elucidate the drug efficacy and safety in affected individuals and the developing fetus, recommendations are inconclusive. Clinicians and patients must make individualized decisions after carefully evaluating the risks and benefits summarized in this article.

Entecavir is a cyclopentyl deoxyguanosine analog that was approved for the treatment of the hepatitis B virus (HBV) in 2005. In Phase III trials, it showed potent HBV suppression with drops of 6- to 7-log copies/mL in HBV DNA at 1 year. In addition, rates of genotypic resistance in nucleos(t)ide-naïve patients are low, reaching only 1.2% after 6 years. Safety and efficacy have been established in compensated cirrhosis and HIV-coinfected patients. Studies in decompensated cirrhosis also show efficacy. Because of potent viral suppression and a large genetic barrier to resistance, entecavir is now a first-line choice in most HBV treatment guidelines and has become an integral part of the HBV treatment armamentarium.

Entecavir is a potent nucleoside inhibitor of the hepatitis B virus (HBV) polymerase with a high antiviral efficacy and a high genetic barrier to viral resistance. After approval in 2006, knowledge on the side effect profile in patients with advanced liver disease and impaired liver function is still limited. Here, we report on 16 patients with liver cirrhosis and chronic hepatitis B who were treated with entecavir. Five of these patients developed lactic acidosis during entecavir treatment. All patients who developed lactic acidosis had highly impaired liver function (Model for End-Stage Liver Disease [MELD] score >or= 20). Lactic acidosis (lactate 26-200 mg/dL, pH 7.02-7.40, base excess -5 mmol/L to -18 mmol/L) occurred between 4 and 240 days after treatment initiation with entecavir. Lactic acidosis was lethal in one patient but resolved in the other cases after termination/interruption of entecavir treatment. No increased lactate serum concentrations were observed during treatment with entecavir in the other 11 patients with chronic hepatitis B and liver cirrhosis who all had MELD scores below 18. The MELD score correlated with the development of lactic acidosis (P < 0.005) as well as its single parameters bilirubin, international normalized ratio, and creatinine. In contrast, Child-Pugh Score did not correlate with the development of lactic acidosis. Our data indicate that entecavir should be applied cautiously in patients with impaired liver function.