Entecavir pharmacokinetics, safety, and tolerability after multiple ascending doses in healthy subjects

Developments in pharmacotherapeutic agents for hepatitis B - how close are we to a functional cure?

INTRODUCTION

Hepatitis B virus (HBV) remains a public health concern given its global prevalence and potential complications including hepatocellular carcinoma (HCC). Current therapies, including nucleos(t)ide analogs (NA) and interferons (IFN), are effective in chronic treatment of HBV but rarely provide a functional cure due to inadequate host response and the presence of viral DNA. Therefore, novel therapies that enhance the innate immune response while suppressing DNA transcription may provide definitive treatment of HBV.

AREAS COVERED

In this review, the authors provide a brief overview of commonly used agents and their efficacy in treatment of HBV. Newer therapies with direct antiviral agents such as bepirovirsen (antisense oligonucleotide (ASO)) and entry inhibitors such as bulevirtide have shown efficacy in reducing viral load but demonstrate further reductions in conjunction with immune modulators such as therapeutic vaccines.

EXPERT OPINION

Combination therapy is far superior to monotherapy alone, necessitating the need for both immunomodulators and direct antiviral agents in chronic treatment of HBV. Therapies that target covalently closed circular (cccDNA) with immunomodulators like therapeutic vaccines have shown promising results and may ultimately achieve functional cure. However, therapies need to be evaluated in the context of the patient, considering both financial and socioeconomic factors.

Assessment of the role of nucleoside transporters, P-glycoprotein, breast cancer resistance protein, and multidrug resistance-associated protein 2 in the placental transport of entecavir using in vitro, ex vivo, and in situ methods

The nucleoside analog entecavir (ETV) is a first-line pharmacotherapy for chronic hepatitis B in adult and pediatric patients. However, due to insufficient data on placental transfer and its effects on pregnancy, ETV administration is not recommended for women after conception. To expand knowledge of safety, we focused on evaluating the contribution of nucleoside transporters (NBMPR sensitive ENTs and Na⁺ dependent CNTs) and efflux transporters, P-glycoprotein (ABCB1), breast cancer resistance protein (ABCG2), and multidrug resistance-associated transporter 2 (ABCC2), to the placental kinetics of ETV. We observed that NBMPR and nucleosides (adenosine and/or uridine) inhibited [³H]ETV uptake into BeWo cells, microvillous membrane vesicles, and fresh villous fragments prepared from the human term placenta, while Na⁺ depletion had no effect. Using a dual perfusion study in an open-circuit setup, we showed that maternal-to-fetal and fetal-to-maternal clearances of [³H]ETV in the rat term placenta were decreased by NBMPR and uridine. Net efflux ratios calculated for bidirectional transport studies performed in MDCKII cells expressing human ABCB1, ABCG2, or ABCC2 were close to the value of one. Consistently, no significant decrease in fetal perfusate was observed in the closed-circuit setup of dual perfusion studies, suggesting that active efflux does not significantly reduce maternal-to-fetal transport. In conclusion, ENTs (most likely ENT1), but not CNTs, ABCB1, ABCG2, and ABCC2, contribute significantly to the placental kinetics of ETV. Future studies should investigate the placental/fetal toxicity of ETV, the impact of drug-drug interactions on ENT1, and interindividual variability in ENT1 expression on the placental uptake and fetal exposure to ETV.

OAT3 Participates in Drug-Drug Interaction between Bentysrepinine and Entecavir through Interactions with M8-A Metabolite of Bentysrepinine-In Rats and Humans In Vitro

Bentysrepinine (Y101) is a novel phenylalanine dipeptide for the treatment of hepatitis B virus. Renal excretion played an important role in the elimination of Y101 and its metabolites, M8 and M9, in healthy Chinese subjects, although the molecular mechanisms of renal excretion and potential drug-drug interactions (DDIs) remain unclear. The present study aimed to determine the organic anion transporters (OATs) involved in the renal disposition of Y101 and to predict the potential DDI between Y101 and entecavir, the first-line agent against HBV and a substrate of OAT1/3. Pharmacokinetic studies and uptake assays using rat kidney slices, as well as hOAT1/3-HEK293 cells, were performed to evaluate potential DDI. The co-administration of probenecid (an inhibitor of OATs) significantly increased the plasma concentrations and area under the plasma concentration-time curves of M8 and M9 but not Y101, while reduced renal clearance and the cumulative urinary excretion of M8 were observed in rats. The time course of Y101 and M8 uptake via rat kidney slices was temperature-dependent. Moreover, the uptake of M8 was inhibited significantly by probenecid and benzylpenicillin, but not by p-aminohippurate or tetraethyl ammonium. M8 was found to be a substrate of hOAT3, but Y101 is not a substrate of either hOAT1 or hOAT3. Additionally, the entecavir inhibited the uptake of M8 in the hOAT3-transfected cells and rat kidney slices in vitro. Interestingly, no significant changes were observed in the pharmacokinetic parameters of Y101, M8 or entecavir, regardless of intravenous or oral co-administration of Y101 and entecavir in rats. In conclusion, M8 is a substrate of OAT3 in rats and humans. Furthermore, M8 also mediates the DDI between Y101 and entecavir in vitro, mediated by OAT3. We speculate that it would be safe to use Y101 with entecavir in clinical practice. Our results provide useful information with which to predict the DDIs between Y101 and other drugs that act as substrates of OAT3.

Antiviral Compounds Screening Targeting HBx Protein of the Hepatitis B Virus

A functional cure of hepatitis B virus (HBV) infection or HB antigen loss is rarely achieved by nucleos(t)ide analogs which target viral polymerase. HBx protein is a regulatory protein associated with HBV replication. We thought to identify antiviral compounds targeting HBx protein by analyzing HBx binding activity. Recombinant GST-tagged HBx protein was applied on an FDA-approved drug library chip including 1018 compounds to determine binding affinity by surface plasmon resonance imaging (SPRi) using a PlexArray HT system. GST protein alone was used for control experiments. Candidate compounds were tested for anti-HBV activity as well as cell viability using HepG2.2.15.7 cells and HBV-infected human hepatocytes. Of the 1018 compounds screened, 24 compounds showed binding to HBx protein. Of the top 6 compounds with high affinity to HBx protein, tranilast was found to inhibit HBV replication without affecting cell viability using HepG2.2.15.7 cells. Tranilast also inhibited HBV infection using cultured human hepatocytes. Tranilast reduced HB antigen level dose-dependently. Overall, theSPRi screening assay identified novel drug candidates targeting HBx protein. Tranilast and its related compounds warrant further investigation for the treatment of HBV infection.

Tenofovir versus lamivudine followed by tenofovir in severe exacerbation of hepatitis B: a randomized controlled study

Spontaneous severe acute exacerbation (SAE) is not uncommon in the natural history of chronic hepatitis B (CHB). Lamivudine (LAM) had the advantages of low price, quick onset, good efficacy and no drug resistance within 24 weeks. This study aimed to compare the short-term efficacy of tenofovir disoproxil fumarate (TDF) and LAM for 24 weeks followed by TDF in the treatment of CHB with severe acute exacerbation. Consecutive patients of CHB with SAE were randomized to receive either TDF (19 patients) or LAM for 24 weeks followed by TDF (18 patients). The primary endpoint was overall mortality or receipt of liver transplantation by week 24. This study was approved by the Institutional Review Board (IRB) of the Kaohsiung Veterans General Hospital (VGHKS12-CT5-10). The baseline characteristics were comparable between the two groups. By week 24, seven (37%) and five (28%) patients in the TDF and LAM/TDF groups died or received liver transplantation (P=0.487). Multivariate analysis showed that albumin level, prothrombin time (PT), and hepatic encephalopathy were independent factors associated with mortality or liver transplantation by week 24. Early reductions in HBV DNA of more than or equal to 2 log at 1 and 2 weeks were similar between the two groups. The biochemical and virological responses at 12, 24 and 48 weeks were also similar between the two groups. TDF and LAM for 24 weeks followed by TDF achieved a similar clinical outcome in CHB patients with SAE.

Identification of a novel long-acting 4'-modified nucleoside reverse transcriptase inhibitor against HBV

BACKGROUND & AIMS

While certain nucleos(t)ide reverse transcriptase inhibitors (NRTIs) are efficacious in treating HBV infection, their effects are yet to be optimized and the emergence of NRTI-resistant HBV variants is an issue because of the requirement for lifelong treatment. The development of agents that more profoundly suppress wild-type and drug-resistant HBVs, and that have a long-acting effect, are crucial to improve patient outcomes.

METHODS

Herein, we synthesized a novel long-acting 4'-modified NRTI termed E-CFCP. We tested its anti-HBV activity in vitro, before evaluating its anti-HBV activity in HBV-infected human-liver-chimeric mice (PXB-mice). E-CFCP's long-acting features and E-CFCP-triphosphate's interactions with the HBV reverse transcriptase (HBV-RT) were examined.

RESULTS

E-CFCP potently blocked HBV_WT^D1 production (IC₅₀^qPCR_cell₌1.8 nM) in HepG2.2.15 cells and HBV_WT^C2 (IC₅₀^SB_cell=0.7 nM), entecavir (ETV)-resistant HBV_ETV-R^{L180M/S202G/M204V} (IC₅₀^SB_cell=77.5 nM), and adefovir-resistant HBV_ADV-R^A181T/N236T production (IC₅₀^SB_cell=14.1 nM) in Huh7 cells. E-CFCP profoundly inhibited intracellular HBV DNA production to below the detection limit, but ETV and tenofovir alafenamide (TAF) failed to do so. E-CFCP also showed less toxicity than ETV and TAF. E-CFCP better penetrated hepatocytes and was better tri-phosphorylated; E-CFCP-triphosphate persisted intracellularly for longer than ETV-triphosphate. Once-daily peroral E-CFCP administration over 2 weeks (0.02~0.2 mg/kg/day) reduced HBV_WT^C2-viremia by 2-3 logs in PXB-mice without significant toxicities and the reduction persisted over 1-3 weeks following treatment cessation, suggesting once-weekly dosing capabilities. E-CFCP also reduced HBV_ETV-R^{L180M/S202G/M204V}-viremia by 2 logs over 2 weeks, while ETV completely failed to reduce HBV_ETV-R^{L180M/S202G/M204V}-viremia. E-CFCP's 4'-cyano and fluorine interact with both HBV_WT-RT and HBV_ETV-R^{L180M/S202G-M204} -RT via Van der Waals and polar forces, being important for E-CFCP-triphosphate's interactions and anti-HBV potency.

CONCLUSION

E-CFCP represents the first reported potential long-acting NRTI with potent activity against wild-type and treatment-resistant HBV.

LAY SUMMARY

Although there are currently effective treatment options for HBV, treatment-resistant variants and the need for lifelong therapy pose a significant challenge. Therefore, the development of new treatment options is crucial to improve outcomes and quality of life. Herein, we report preclinical evidence showing that the anti-HBV agent, E-CFCP, has potent activity against wild-type and treatment-resistant variants. In addition, once-weekly oral dosing may be possible, which is preferrable to the current daily dosing regimens.

New therapeutic options for persistent low-level viremia in patients with chronic hepatitis B virus infection: Increase of entecavir dosage

Chronic hepatitis B virus (HBV) infection (CHB) is a public health concern worldwide. Current therapies utilizing nucleos(t)ide analogs (NA) have not resulted in a complete cure for CHB. Furthermore, patients on long-term NA treatment often develop low-level viremia (LLV). Persistent LLV, in addition to causing the progression of liver disease or hepatocellular carcinoma, may shed light on the current plight of NA therapy. Here, we review the literature on LLV, NA treatment, and various doses of entecavir to find a strategy for improving the efficacy of this antiviral agent. For LLV patients, three therapeutic options are available, switching to another antiviral monotherapy, interferon-α switching therapy, and continuing monotherapy. In real-world clinical practice, entecavir overdose has been used in antiviral therapy for CHB patients with NA refractory and persistent LLV, which encouraged us to conduct further in-depth literature survey on dosage and duration related entecavir studies. The studies of pharmacodynamics and pharmacokinetics show that entecavir has the maximal selected index for safety, and has great potential in inhibiting HBV replication, in all of the NAs. In the particular section of the drug approval package published by the United States Food and Drug Administration, entecavir doses 2.5-20 mg/d do not increase adverse events, and entecavir doses higher than 1.0 mg/d might improve the antiviral efficacy. The literature survey led us to two suggestions: (1) Increasing entecavir dose to 1.0 mg/d for the treatment of NA naïve patients with HBV DNA >2 × 10⁶ IU/mL is feasible and would provide better prognosis; and (2) Further research is needed to assess the long-term toxic effects of higher entecavir doses (2.5 and 5.0 mg/d), which may prove beneficial in treating patients with prior NA treatment, partial virological response, or LLV state.

Sequential therapy from entecavir to tenofovir alafenamide versus continuous entecavir monotherapy for patients with chronic hepatitis B

Background and Aim

Although tenofovir alafenamide (TAF), as well as entecavir (ETV), is widely used as first‐line treatment for patients with chronic hepatitis B, there are only a few studies comparing sequential therapy from ETV to TAF and continuous ETV monotherapy in patients with maintained virologic response to ETV.

Methods

In a retrospective multicenter study, we investigated the efficacy and safety of sequential therapy from ETV to TAF (ETV‐TAF group) and compared them with continuous ETV monotherapy (ETV group), using propensity score matching, in chronic hepatitis B patients.

Results

From 442 patients, we analyzed 142 patients from each group comprising 71 patients matched for several data, including age, HBV genotype, hepatitis B envelope antigen, cirrhosis, alanine aminotransferase, platelet count, prior ETV monotherapy period, and hepatitis B surface antigen (HBsAg) change during prior ETV monotherapy. In the ETV‐TAF group, HBsAg levels significantly decreased from baseline to 48 weeks after switching to TAF (−0.02 log IU/mL, P = 0.038). HBcrAg levels also significantly decreased after switching to TAF (−0.1 log IU/mL, P = 0.004). However, there were no significant differences in the reduction of HBsAg and HBcrAg levels between the ETV‐TAF and ETV groups. There was no significant difference in the change of estimated glomerular filtration rate levels from baseline to 48 weeks between the two groups.

Conclusions

The present study indicated that the efficacy, especially of the HBsAg‐reducing action, and safety of sequential therapy from ETV to TAF were similar to those of continuous ETV monotherapy among chronic hepatitis B patients with maintained virologic response to ETV.

Treatment with tenofovir disoproxil fumarate or entecavir in chronic hepatitis B virus-infected patients with renal impairment: results from a 7-year, multicentre retrospective cohort study

BACKGROUND

Limited data exist regarding tenofovir disoproxil fumarate (TDF) safety and effectiveness in chronic hepatitis B virus-infected (CHB) patients with renal impairment (RI).

AIMS

To compare real-world data on renal safety and effectiveness of TDF vs entecavir (ETV) in CHB patients with moderate-to-severe RI.

METHODS

Retrospective, non-interventional, cohort study analysing medical records for TDF/ETV-treated CHB patients (54 European centres). Included patients experienced moderate-to-severe RI (creatinine clearance 20-60 mL/min [Cockcroft-Gault]) either before TDF/ETV initiation ('before' subgroup [baseline = treatment initiation]) or after TDF/ETV initiation ('after' subgroup [baseline = first RI occurrence]). The primary objective was TDF safety, particularly renal-related adverse events of special interest (AESI). TDF and ETV safety and effectiveness were compared and multivariate analyses were performed using inverse probability treatment weighting.

RESULTS

'Before' subgroup included 107 TDF- and 91 ETV-treated patients; 'after' subgroup included 212 TDF- and 77 ETV-treated patients. Mean baseline creatinine clearance was higher for TDF- vs ETV-treated patients (both subgroups). Median follow-up was 3.1 years (both treatments). AESI were more frequent with TDF vs ETV ('before': 18.7% vs 8.8%; 'after': 9.9% vs 3.9%); however, differences were not significant by multivariate analysis. Only TDF-treated patients experienced renal tubular dysfunction (6.5% 'before'; 1.9% 'after') as well as renal adverse events leading to treatment discontinuation (8.4% 'before'; 7.1% 'after'). Effectiveness was similar between treatments.

CONCLUSIONS

Overall safety was similar for TDF vs ETV (both subgroups). Given that renal tubular dysfunction occurred with TDF and not with ETV, renal safety concerns may be greater with TDF in CHB patients with RI.

Pregnancy Impacts Entecavir Pharmacokinetics but Does Not Alter Its Renal Excretion

Entecavir (ETV) is a first-line antiviral drug against the hepatitis B virus. This study was designed to investigate whether ETV pharmacokinetics changes during pregnancy and the underlying mechanism. The results showed that ETV exposure in plasma was higher in pregnant rats than in nonpregnant rats, whereas the exposure after delivery was recovered to that in nonpregnant rats. Because 70% of orally dosed ETV is eliminated by kidney, the effects of estradiol (E2) and progesterone (P4), 2 important hormones during pregnancy, on ETV-related renal transporters were investigated. Our results revealed that the activities of the ETV-related renal transporters hOAT1, hOAT3, hMATE1, and hMATE2-K were clearly inhibited by E2 and P4, resulting in reduced ETV accumulation in transporter-transfected cell models. However, the cumulative urinary excretion of ETV in pregnant rats exhibited no significant difference compared to nonpregnant rats, although the endogenous creatinine clearance in pregnant rats was 1.5-fold that of nonpregnant rats. In conclusion, ETV plasma exposure is increased during pregnancy, but ETV renal excretion displays no significant alteration. This may be because, during pregnancy, increased glomerular ETV filtration compensated for the decrease in renal tubular ETV secretion that occurs by E2- and P4-mediated inhibition of related transporters.

A First-in-Human Trial of GLS4, a Novel Inhibitor of Hepatitis B Virus Capsid Assembly, following Single- and Multiple-Ascending-Oral-Dose Studies with or without Ritonavir in Healthy Adult Volunteers

GLS4 is a novel inhibitor of the hepatitis B virus (HBV) capsid assembly with inhibitory activities against nucleot(s)ide-resistant HBV strains. This study investigated the pharmacokinetics, safety, and tolerability of GLS4 and the effects of food and ritonavir in healthy adults. GLS4 was administered in a single-ascending-dose study over 1 to 240 mg and multiple-ascending-dose study that ranged from 30 mg once daily to 180 mg three times daily. The drug interaction study included sequential design (day 1 for 120 mg GLS4 alone, day 5 for 100 mg ritonavir alone, followed by 9 days of both drugs) and a placebo control (9 days of both 240 mg GLS4 and 100 mg ritonavir). The results showed that the steady-state trough concentration of multiple dosing of GLS4 alone was significantly lower than the 90% effective concentration of 55.7 ng/ml, even with increasing dosing frequency and dosage. An initial dose of 100 mg ritonavir significantly boosted plasma concentration at 24 h of 120 mg GLS4 from 2.40 to 49.8 ng/ml (geometric mean ratio, 20.7; 90% confidence interval, 17.0 to 25.3), while a milder effect was observed on the area under the curve from 0 to 24 h, with a 7.42-fold increase, and on the maximum concentration, with a 4.82-fold increase. The pharmacokinetics change in GLS4 persisted after 9 days of chronic dosing, with a trough concentration of 182 ng/ml. Both single and multiple doses of GLS4 up to 240 mg with or without ritonavir were well tolerated. These results support the investigation of a novel HBV treatment regimen containing GLS4 with 100 mg ritonavir added solely to enhance GLS4 concentrations in plasma. (This study was registered at the China Platform for Registry and Publicity of Drug Clinical Trials [http://www.chinadrugtrials.org.cn] under numbers CTR20132137 and CTR20150230.).

The combination therapy of Peginterferonα and entecavir for HBeAg-positive chronic hepatitis B with high HCC risk

The population of HBV infection with family history of hepatocellular carcinoma (HCC) is the high risk group for the development of HCC. The aim of this study was to evaluate the effect of the de novo combination therapy including pegylated-interferon α-2a (PEG-IFNα-2a) and entecavir (ETV) in this high risk population. The study recruited 58 Hepatitis B e Antigen (HBeAg)-Positive CHB patients patients with HBV-DNA > 10⁷ IU/mL, genotype B or C and HCC family history and were treated for 48 weeks. Patients without HBeAg loss at the 48th week were 40 patients and extended the combination therapy to 96 weeks. All patients were followed up to 120 weeks. The rate of HBeAg loss and HBsAg loss was 12/40(30.0%) and 2/40(5.0%) at week 120 respectively. When logistic regression analysis was used to identify viables of HBeAg loss, HBV-DNA levels <20 IU/mL at week 48 was found to have a 6.02 fold increased probability (95% CI = 1.17-30.40, P = .03) of HBeAg loss. Patients with HBV-DNA levels <20 IU/mL at week 48 had a high probability of HBeAg loss 8/17(47.1%), HBsAg loss 2/17(11.8%), compared to 4/23(17.4%), 0/23(0%) in patients with HBV-DNA ≥ 20 IU/mL. Combination therapy for 96 weeks was well tolerated. During the combination therapy, low-level viremia during treatment is reversely associated with response. The combination therapy of PEG-IFNα and ETV was suggested to extend to 96 weeks when HBV-DNA was completed suppressed at week 48.

Correlation Between Serum Entecavir Concentration and Virological Response in Patients with Chronic Type B Hepatitis

Background

This study was conducted to investigate the relationship between trough concentrations of serum entecavir and the virological response of patients with chronic type B hepatitis (CHB).

Material/Methods

A total of 59 CHB patients who had been receiving antiviral therapy with entecavir for >3 months were included in this study. Serum entecavir concentrations, HBV DNA levels, and other biochemical indicators were determined after drug treatments.

Results

The serum entecavir concentrations in the good response and poor response groups were 0.58±0.38 and 0.43±0.15 ng/mL, respectively. The antiviral efficacy was 52.38%, 65.63%, and 100% in low, middle, and high entecavir groups, respectively. The baseline HBV DNA level among the patients with poor response was significantly higher than in the group with good response. Among the 14 patients with a high viral load, 5 patients showed a good response and had a higher entecavir concentration than the other 9 patients with poor response. Entecavir in patients with cirrhosis was higher than in those without cirrhosis (0.63±0.45 ng/mL vs. 0.46±0.16 ng/mL), and the virological response rate in patients with cirrhosis was higher than in those without cirrhosis (83.33 vs. 51.43%). Cirrhosis progression was reversed in 3 patients with high serum entecavir concentration.

Conclusions

Serum entecavir concentrations vary among individuals, and higher serum entecavir concentration is correlated with more efficient viral clearance. Therefore, for patients with poor response, high doses may be beneficial for viral clearance.

Contrasting Timing of Virological Relapse After Discontinuation of Tenofovir or Entecavir in Hepatitis B e Antigen-Negative Patients

Stopping long-term nucleos(t)ide analogue therapy increases hepatitis B virus (HBV) surface antigen (HBsAg) loss rates in HBV e antigen (HBeAg)-negative patients. Viral rebound may induce immune responses facilitating functional cure. We analyzed which factors are associated with timing of virological relapse in 220 Asian HBeAg-negative patients from the prospective ABX203 vaccine study. Unexpectedly, only the type of antiviral therapy was significantly associated with early virological relapse, defined as an HBV DNA load of >2000 IU/mL until week 12, and relapse occurred earlier in patients treated with tenofovir versus those treated with entecavir (median time, 6 vs 24 weeks; P < .0001). This should be considered for future trials and monitoring of patients after treatment discontinuation.

Switching from entecavir to tenofovir alafenamide versus maintaining entecavir for chronic hepatitis B

Tenofovir alafenamide (TAF) is a newly developed prodrug of tenofovir (TFV). We divided 48 chronic hepatitis B patients who had taken entecavir (ETV) for ≥2 years into two groups: the ETV continuation (n = 24) and the TAF switching (n = 24) groups, and compared the antiviral effects and safety until 48 weeks after the start of the study. There were no significant differences in the alterations in the serum levels of HBs antigen (HBsAg) level between the ETV continuation and the TAF switching groups at 24 or 48 weeks. We also examined the effect of baseline HBsAg level on the decrease of HBsAg during the treatment; in the TAF switching group, the decrease of HBsAg level at 48 weeks was more significant in patients with low baseline HBsAg (<800 IU/mL) than those with high baseline HBsAg ( >800 IU/mL) (change of HBsAg; - 0.029 vs - 0.132 for high and low baseline HBsAg, respectively, P = .007). Also, the effect on renal function was found to be comparable between the TAF switch group and the ETV continuation group. In this study, switching from ETV to TAF may represent higher efficacy for a decrease of HBsAg than a continuation of ETV among the patients with low baseline HBsAg level.

Entecavir-loaded poly (lactic-co-glycolic acid) microspheres for long-term therapy of chronic hepatitis-B: Preparation and in vitro and in vivo evaluation

To avoid severe exacerbations in the load of hepatitis B virus (HBV) as a consequence of discontinuous use of anti-HBV drugs, entecavir (ETV), the first-line anti-HBV drug, was primally formulated as extended-release poly (lactic-co-glycolic acid) microspheres in the present study. Because ETV is slightly soluble in water and in some other organic solvents used for microsphere preparation, methods for solid-microencapsulation were employed to fabricate the ETV microspheres. The optimized microspheres were evaluated for their morphology, particle size, drug loading, in vitro drug release, and in vivo pharmacokinetics in rats. The optimized formulation was found to have a mean particle size of 86 µm and drug loading of 13%. Differential scanning calorimetry and powder X-ray diffraction indicated that ETV existed in crystal, amorphous, and molecular states in the microspheres. In vitro and in vivo release revealed that the dissolution of ETV dominated the release process. The morphology of the microspheres and changes in the morphology during in vitro release were assessed by scanning electron microscopy. The novel ETV-MS described in this study should have great potential for clinical use as an alternative treatment against HBV.

Concomitant food intake does not affect the efficacy of entecavir in chronic hepatitis B patients with virological response: a randomized, multicenter, noninferiority trial

Background

Little clinical data are available about the effect of food on the antiviral efficacy of entecavir for chronic hepatitis B virus (HBV) infection. The present study evaluated whether entecavir administration in the fed state had comparable efficacy to the fasted condition for maintenance of viral suppression in HBV-infected patients with virological response on entecavir therapy.

Methods

In this multicenter, randomized, open-label, noninferiority study, patients who were currently receiving entecavir and showed a serum HBV DNA level of <20 IU/mL were randomized to take entecavir either under the fasted or fed condition for 48 weeks.

Results

We randomly assigned 50 patients to the fasted group and 46 patients to the fed group. The full analysis set consisted of 49 patients in the fasted group and 44 patients in the fed group. At week 48, the proportion of patients with HBV DNA <20 IU/mL was not significantly different between the fasted and fed groups (98% vs 100%, P=1.00). The mean log₁₀ HBV DNA changes from baseline were similar between the two groups (−0.004 vs −0.012 log₁₀ IU/mL, P=0.43). There were no significant differences in the proportions of patients with normal alanine aminotransferase (87.8% vs 95.5%, P=0.27) and hepatitis B e-antigen seroconversion (0% vs 6.7%, P=0.47) between the two groups. None of the patients showed viral breakthrough. In pharmacokinetic analysis, the maximum concentration and the area under the concentration– time curve to the last quantifiable concentration decreased by 26.4% and 9.3%, respectively, in the fed group compared with the fasted group. However, the differences between two groups were not statistically significant (P=0.28 and 0.83, respectively).

Conclusion

In patients with virological response under entecavir therapy, concomitant food intake did not affect the antiviral efficacy. For patients with adherence problem, taking entecavir with food may be considered to improve compliance.

Multiple Drug Transporters Are Involved in Renal Secretion of Entecavir

Entecavir (ETV) is a first-line antiviral agent for the treatment of chronic hepatitis B virus infection. Renal excretion is the major elimination path of ETV, in which tubular secretion plays the key role. However, the secretion mechanism has not been clarified. We speculated that renal transporters mediated the secretion of ETV. Therefore, the aim of our study was to elucidate which transporters contribute to the renal disposition of ETV. Our results revealed that ETV (50 μM) remarkably reduced the accumulation of probe substrates in MDCK cells stably expressing human multidrug and toxin efflux extrusion proteins (hMATE1/2-K), organic cation transporter 2 (hOCT2), and carnitine/organic cation transporters (hOCTNs) and increased the substrate accumulation in cells transfected with multidrug resistance-associated protein 2 (hMRP2) or multidrug resistance protein 1 (hMDR1). Moreover, ETV was proved to be a substrate of the above-described transporters. In transwell studies, the transport of ETV in MDCK-hOCT2-hMATE1 showed a distinct directionality from BL (hOCT2) to AP (hMATE1), and the cellular accumulation of ETV in cells expressing hMATE1 was dramatically lower than that of the mock-treated cells. The accumulation of ETV in mouse primary renal tubular cells was obviously affected by inhibitors of organic anion transporter 1/3 (Oat1/3), Oct2, Octn1/2, and Mrp2. Therefore, the renal uptake of ETV is likely mediated by OAT1/3 and OCT2 while the efflux is mediated by MATEs, MDR1, and MRP2, and OCTN1/2 may participate in both renal secretion and reabsorption.

Entecavir plasma concentrations are inversely related to HBV-DNA decrease in a cohort of treatment-naïve patients with chronic hepatitis B

The role of therapeutic drug monitoring (TDM) of entecavir (ETV) in the treatment of patients affected by chronic hepatitis B (CHB) has not yet been defined. Here we present an interim analysis regarding the role of ETV TDM in a prospective cohort of treatment-naïve patients with CHB who received this treatment. The results from 40 patients consecutively enrolled at our centre from 2010 to 2013 are described. The primary endpoint was the evaluation of the role of ETV plasma concentrations in the kinetics of hepatitis B virus (HBV) DNA decrease. Minimum ETV concentrations (Ctrough) were measured every month after the start of therapy for the first 3 months and then every 6 months. The main result of the pharmacokinetic analysis was the significant inverse correlation of ETV concentration after 1 month of treatment and HBV-DNA decrease after 3 months of treatment (r = -0.624; P <0.001). This correlation was also confirmed when stratifying patients on the basis of viral genotypes: A (r = -0.719; P = 0.003); C (r = -0.917; P = 0.007); and D (r = -0.760; P = 0.007). Possible explanations for this phenomenon could involve interpatient differences in liver conditions (tissue damage or inflammation) and/or genetic variability in specific drug transporters. Further investigations are needed to confirm these results quantifying ETV concentration in peripheral blood mononuclear cells as well as in a larger cohort.

Entecavir Interacts with Influx Transporters hOAT1, hCNT2, hCNT3, but Not with hOCT2: The Potential for Renal Transporter-Mediated Cytotoxicity and Drug-Drug Interactions

Entecavir (ETV) is one of the most potent agents for the treatment of the hepatitis B viral infection. The drug is principally eliminated by the kidney. The goal of this study was to investigate the potential of ETV to interact in vitro with the renal SLC transporters hOAT1, hOCT2, hCNT2 and hCNT3. Potential drug–drug interactions of ETV at the renal transporters with antiviral drugs known to be excreted by the kidney (adefovir, tenofovir, cidofovir) as well as transporter-dependent cytotoxicity were also examined. Interactions with the selected transporters along with cytotoxicity were studied in several transiently transfected cellular models using specific substrates and inhibitors. ETV was found to be both a substrate and inhibitor of hOAT1 (IC₅₀ = 175.3 μM), hCNT2 (IC₅₀ = 241.9 μM) and hCNT3 (IC₅₀ = 278.4 μM) transporters, although it interacted with the transporters with relatively low affinities. ETV inhibited the cellular uptake of adefovir, tenofovir, and cidofovir by hOAT1; however, effective inhibition was shown at ETV concentrations exceeding therapeutic levels. In comparison with adefovir, tenofovir, and cidofovir, ETV displayed no transporter-mediated cytotoxicity in cells transfected with hOAT1, hCNT2, and hCNT3. No significant interaction of ETV with hOCT2 was detected. The study demonstrates interactions of ETV with several human renal transporters. For the first time, an interaction of ETV with the hCNTs was proved. We show that the potency of ETV to cause nephrotoxicity and/or clinically significant drug-drug interactions related to the tested transporters is considerably lower than that of adefovir, tenofovir, and cidofovir.

An injectable liquid crystal system for sustained delivery of entecavir

Liquid crystal (LC) technology has attracted much interest for new injectable sustained-release (SR) formulations. In this study, an injectable liquid crystal-forming system (LCFS) including entecavir was prepared for the treatment of hepatitis B. In particular, an anchoring effect was introduced because LCFSs are relatively hydrophobic while entecavir is a slightly charged drug. The physicochemical properties of LCFSs were investigated by cryo-transmission electron microscopy (cryo-TEM), polarized optical microscopy, and small-angle X-ray scattering (SAXS), showing typical characteristics of the liquid crystalline phase, which was classified as the hexagonal phase. A pharmacokinetic study in rats showed sustained release of entecavir for 3-5 days with a basic LCFS formulation composed of sorbitan monooleate (SMO), phosphatidyl choline (PC), and tocopherol acetate (TA) as the main LC components. 1,2-Dipalmitoyl-sn-glycero-3-phosphatidic acid (DPPA), an anionic phospholipid, was added to increase the anchoring effect between the cationic entecavir and the anionic DPPA, which resulted in a 1.5-times increase in half-life in rats. In addition, anchoring was strengthened by optimizing the pH to 2.5-4.5, increasing the half-life in the rat and dog. Also, due to the increasing terminal half-life from rat to dog resulting from species differences, LCFS produced one week delivery of entecavir in rat and two weeks delivery in dog. Therefore, LCFS injection using the anchoring effect for entecavir can potentially be used to deliver the drug over more than 2 weeks or even 1 month for the treatment of hepatitis B.

Similar response to entecavir 0.5 and 1.0 mg in treatment-naïve chronic hepatitis B patients: a case-control study

BACKGROUND AND AIMS

The dose recommendation for entecavir (ETV) is 0.5 mg daily for treatment-naïve chronic hepatitis B (CHB) patients and 1.0 mg daily for lamivudine-refractory patients; however, few data are available for the efficacy of a 1.0-mg daily dose in treatment-naïve CHB patients. Our goal is to examine the treatment outcome of treatment-naïve patients placed on ETV 0.5 mg or ETV 1.0 mg daily through week 48.

METHODS

Cases were 40 consecutive hepatitis B e antigen (HBeAg)-positive CHB patients treated with ETV 1.0 mg daily between January 2005 and September 2010, and controls were 40 consecutive CHB patients treated with ETV 0.5 mg daily between January 2005 and September 2010 at three US gastroenterology/liver clinics. Controls were matched for age (±5 years), sex, HBeAg, and baseline hepatitis B virus (HBV) DNA (±0.5 log10 IU/ml). Complete viral suppression was defined as undetectable HBV DNA by polymerase chain reaction (<100 IU/ml).

RESULTS

Both groups had similar distributions of age (38 ± 11 years), male patients (55 %), and mean HBV DNA (7.7 ± 1.1 log10 IU/ml). The complete viral suppression rate was similar in both cases and controls through week 24 (15 vs. 15 %, p = 1.00) and week 48 (22 vs. 36 %, p = 0.17). Non-adherence was reported in three patients in the ETV 1.0 mg daily cohort at week 48.

CONCLUSIONS

There were no significant differences in the proportion of patients with complete viral suppression in patients treated with ETV 0.5 mg daily or the higher daily dose of 1.0 mg.

The Discovery and Development of a Potent Antiviral Drug, Entecavir, for the Treatment of Chronic Hepatitis B

Since the first approval of interferon for the treatment of chronic hepatitis B virus (HBV) infection in 1992, six additional antivirals have been developed: pegylated interferon-alfa2a, and the oral antivirals lamivudine, adefovir, telbivudine, entecavir and tenofovir. The availability of animal models for HBV infection and hepatocyte cell culture led to the discovery and development of oral antivirals targeted at HBV polymerase and reverse transcriptase, which inhibit viral replication. The discovery and development of entecavir, the first oral anti-HBV drug with both potent antiviral activity and a high genetic barrier to resistance, took more than 10 years before it was first approved in the USA. Since then, multiple real-life studies have provided data consistent with the findings of the registration trials and the long-term rollover study in terms of efficacy, resistance, and safety. Data from the long-term follow-up of patients enrolled in the registration studies showed that treatment with entecavir can lead to significant improvements in liver histopathology, and recent cohort studies have demonstrated that treatment with entecavir may reduce disease progression and the development of hepatocellular carcinoma (HCC) in patients with chronic hepatitis B. In addition, real-life studies suggest that entecavir may reduce HCC recurrence and increase survival rates in patients with HBV-related HCC post-surgical resection.

Response to higher dose of entecavir 1.0 mg daily in patients with partial response to entecavir 0.5 mg daily

BACKGROUND

Despite its high potency against hepatitis B virus (HBV), entecavir (ETV) 0.5 mg daily may not be sufficient to induce complete viral suppression in some patients with very high pretreatment viremia. It is not clear whether ETV 1.0 mg daily would have additive effect in such patients.

GOALS

Our goal was to examine virologic outcome of ETV 1.0 mg daily in patients with partial response to ETV 0.5 mg daily.

METHODS

We retrospectively studied 31 consecutive treatment-naive patients who were switched to ETV 1.0 mg daily after partial response [reduction of HBV DNA ≥2 log10 IU/mL but with detectable HBV DNA levels (>100 IU/mL) after 24 weeks of therapy or longer] with ETV 0.5 mg daily from January 2005 to January 2010 at 2 clinics.

RESULTS

All patients were Asians and 90% had positive hepatitis B e antigen. Mean HBV DNA was 8.04±0.65 log10 IU/mL before therapy and 3.64±0.91 log10 IU/mL at the time of switch. Overall rate of complete viral suppression were 29% (n=9/31) after 24 weeks of ETV 1.0 mg daily and 22% (n=5/23) after 48 weeks. Complete viral suppression after 24 weeks with ETV 1.0 mg daily was significantly higher in patients with lower HBV DNA (<3 log10 IU/mL) at time of switch: 75% versus 5%, P<0.0001.

CONCLUSIONS

The majority of patients with partial response to ETV 0.5 mg daily did not achieve complete viral suppression with the higher dose of ETV 1.0 mg daily except those with minimal residual viremia (HBV DNA <3 log10 IU/mL).

Entecavir for the treatment of patients with hepatitis B virus-related decompensated cirrhosis

INTRODUCTION

Chronic hepatitis B (CHB) infection is common and carries a significant risk for the development of cirrhosis, hepatic decompensation, and hepatocellular carcinoma. The goal of treatment in patients with CHB-related decompensated cirrhosis is to improve hepatic dysfunction and reduce mortality through the inhibition of viral replication. Several studies have now shown nucleot(s)ide analogs to be safe and effective in decompensated cirrhosis due to CHB.

AREAS COVERED

A review of the evidence for the use of entecavir in the treatment of decompensated hepatitis B cirrhosis is discussed.

EXPERT OPINION

Entecavir is an effective treatment option for most patients with CHB. In treatment naïve patients, it is a potent antiviral agent with a very low resistance rate, making it an excellent option for the treatment of decompensated hepatitis B cirrhosis. The use of entecavir monotherapy in patients with a known rtM204V lamivudine-resistant mutation should be avoided due to increased risk of developing entecavir resistance and failing treatment.

Entecavir: a review of its use in the treatment of chronic hepatitis B in patients with decompensated liver disease

The oral deoxyguanosine nucleoside analogue entecavir (Baraclude®) has potent activity against hepatitis B virus (HBV) and a high genetic barrier to resistance. This article reviews the clinical efficacy and tolerability of entecavir in the treatment of chronic hepatitis B in patients with decompensated liver disease, as well as summarizing its pharmacological properties. Entecavir 1 mg/day was more effective than adefovir dipivoxil 10 mg/day in the treatment of patients with chronic hepatitis B and decompensated liver disease, according to the results of a randomized, open-label, multicentre trial. Patients were either nucleos(t)ide naive or lamivudine experienced. The reduction from baseline in HBV DNA levels at week 24 (primary endpoint) was significantly greater with entecavir than with adefovir dipivoxil. The proportion of patients with HBV DNA levels of <300 copies/mL was also significantly greater with entecavir than with adefovir dipivoxil at weeks 24, 48 and 96, as was the proportion of patients with ALT normalization. Entecavir 0.5 or 1 mg/day, tenofovir disoproxil fumarate 300 mg/day and a fixed-dose combination of emtricitabine/tenofovir disoproxil fumarate 200 mg/300 mg per day were effective in the treatment of chronic hepatitis B in patients with decompensated liver disease, according to the 48-week analysis of a randomized, double-blind, multicentre trial, primarily designed to examine tolerability endpoints. In this trial, over one-third of patients had received previous therapy with lamivudine for ≥6 months. The efficacy of entecavir in treatment-naive patients with HBV-related decompensated cirrhosis did not significantly differ from that seen in patients with chronic hepatitis B or compensated cirrhosis (compensated group), according to the results of a prospective, nonrandomized study. After 6 or 12 months of entecavir treatment, there were no significant differences between the decompensated and compensated groups in virological, biochemical or serological endpoints. In patients with decompensated cirrhosis, significant improvements from baseline in liver function were seen after 12 months of entecavir therapy. Oral entecavir was generally well tolerated in patients with chronic hepatitis B and decompensated liver disease, with most of the reported treatment-emergent adverse events consistent with decompensated liver disease. In the trial primarily designed to examine tolerability endpoints, there was no significant difference between patients receiving entecavir and those receiving tenofovir disoproxil fumarate with or without emtricitabine in terms of the proportion of patients experiencing tolerability failure or the proportion of patients with confirmed increases in serum creatinine levels of ≥0.5 mg/dL above baseline or confirmed serum phosphorus levels of <2.0 mg/dL at week 48 (co-primary endpoints). It has been suggested that the risk of lactic acidosis associated with oral nucleos(t)ide analogue therapy is increased in patients with highly impaired liver function. However, only one case of lactic acidosis was reported among entecavir recipients across two clinical trials in patients with chronic hepatitis B and decompensated liver disease. Moreover, small studies found that the risk of lactic acidosis was not increased in patients with chronic hepatitis B and decompensated liver disease who received entecavir, compared with patients with non-HBV decompensated liver disease. In conclusion, entecavir is a valuable agent for the first-line treatment of chronic hepatitis B in patients with decompensated liver disease.

Response to tenofovir monotherapy in chronic hepatitis B patients with prior suboptimal response to entecavir

Both entecavir (ETV) and tenofovir (TDF) are potent antiviral agents for hepatitis B virus (HBV). Suboptimal response (SOR) following antiviral therapy is associated with an increased risk of subsequent treatment failure and viral resistance. It remains unclear whether switching to TDF is a reasonable approach in patients with SOR to ETV treatment. This study was aimed to determine how HBV patients with SOR to ETV respond to TDF monotherapy. Data of patients with SOR to ETV (failure to achieve >1 log(10) HBV-DNA reduction during the last 24 weeks of ETV treatment) who were switched to TDF monotherapy during 2005 and 2010 were reviewed. Treatment adherence was assessed by pill-count. Fourteen patients (2.9%) were identified from a total cohort of 482 ETV-treated patients. All 14 patients were Chinese and were infected with HBV genotype C (71%) or B (29%). Nine patients were men, and the median age was 41.5 years (19-64). Twelve were treatment naïve (one lamivudine- and one peginterferon-experienced patient); 85.7% were HBeAg positive. The median baseline HBV-DNA was 7.55 (5.30-9.40) log(10) copies/mL, and 57% had abnormal serum alanine aminotransferase (ALT) levels. Precore and/or basal core promoter mutations were detected in four patients, whereas no genotypic resistance was detected at baseline and before switching to TDF. The median duration of ETV treatment was 64.5 (26-126) weeks. The median HBV-DNA at the time of switching to TDF was 3.69 (3.00-4.90) log(10) copies/mL. The median HBV-DNA reduction from baseline and during the last 6-month observation period prior to switching to TDF was 4.04 (0.51-6.06) log(10) and 0.43 (-0.09-1.13) log(10) copies/mL, respectively. After the switching to TDF, all 14 patients (100%) achieved undetectable HBV-DNA and ALT normalization within a median duration of 30 weeks. In 12 patients who were HBeAg positive, HBeAg seroconversion was observed in two patients after TDF treatment of 75- and 84-weeks duration. There was no virological breakthrough observed after switching to TDF with a median follow-up period of 50 (24-160) weeks. TDF treatment was safe and well tolerated. In conclusion, suboptimal response to ETV is rare (approximately 3%). TDF monotherapy is safe and very effective in the management of HBV patients with SOR to ETV.

Selection of chronic hepatitis B therapy with high barrier to resistance

Antiviral drug resistance is a crucial factor that frequently determines the success of long-term therapy for chronic hepatitis B. The development of resistance to nucleos(t)ide analogues has been associated with exacerbations in liver disease and increased risk of emergence of multidrug resistance. The selection of a potent nucleos(t)ide analogue with a high barrier to resistance as a first-line therapy, such as entecavir or tenofovir, provides the best chance of achieving long-term treatment goals and should be used wherever possible. The barrier to resistance of a given nucleos(t)ide analogue is influenced by genetic barrier, drug potency, patient adherence, pharmacological barrier, viral fitness, mechanism of action, and cross-resistance. In countries with limited health-care resources, the selection of a therapy with a high barrier to resistance is not always possible and alternative strategies for preventing resistance might be needed, although limited data are available to support these strategies.

Salting-out homogeneous liquid-liquid extraction approach applied in sample pre-processing for the quantitative determination of entecavir in human plasma by LC-MS

A convenient, robust, economical and selective sample preparation method for the quantitative determination of entecavir in human plasma by LC-MS was developed and validated. Entecavir and the internal standard of acyclovir were extracted from 500 μL of human plasma by a salting-out homogeneous liquid-liquid extraction approach (SHLLE) with acetonitrile as the organic extractant and magnesium sulfate as the salting-out reagent. They were analyzed on a Hanbon® Lichrospher RP C18 HPLC column (150 mm×2.0 mm; 5 μm) with gradient elution. The mobile phase comprised 0.1% acetic acid-0.2 mmol ammonium acetate in water (mobile phase A) and acetonitrile (mobile phase B). The flow rate is 0.2 mL/min. The analytes were detected by a LC-MS 2010 single quadrupole mass spectrometer instrument equipped with an electrospray ionization interface using selective ion monitoring positive mode. A "post cut" column switch technique was incorporated into the method to remove interferences of earlier and later eluting matrix components than entecavir and internal standard, including salting-out reagent used in sample pre-processing. The method was validated over the concentration range of 0.05-20 ng/mL. The intra-day and inter-day precision of the assay, as measured by the coefficient of variation (%CV), was within 3.59%, and the intra-day assay accuracy was found to be within 4.88%. The average recovery of entecavir was about 50% and the ion suppression was approximately 44% over the standard curve. Comparison of matrix effect between SHLLE and SPE by continuous post column infusion showed that these two methods got similar, slight ion suppression. The SHLLE method has been successfully utilized for the analysis of entecavir in post-dose samples from a clinical study.

LC-ESI-MS/MS method for the quantification of entecavir in human plasma and its application to bioequivalence study

Liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) was used for a quantitative estimation of entecavir (EV) in human plasma using lamivudine (LM) as internal standard (IS). The method herein described is simple, sensitive, and specific. Chromatographic separation was performed on XBridge-C18, 4.6 mm × 50 mm, 5-μm column with an isocratic mobile phase composed of 10 mM ammonium hydrogen carbonate (pH 10.5):methanol (85:15 v/v), pumped at 0.3 ml/min. EV and LM were detected using proton adducts at m/z 278.1→152.1 and 230.2→112.0 in multiple reaction monitoring (MRM) positive mode. Solid phase extraction method was employed in the extraction of EV and LM from the biological matrix. This method was validated over a linear concentration range of 50.0-20000.0 pg/ml with a correlation coefficient (r) ≥0.9983. Intra and inter-day precision of EV was found within the range of 1.2-4.2 for EV and 4.4-4.5 for LM. EV was stable throughout three freeze/thaw cycles, bench top and postoperative studies. This method was successfully used in the analysis of plasma samples following oral administration of EV (0.5 mg) in 26 healthy human volunteers.

Entecavir: a review of its use in chronic hepatitis B

Entecavir (Baraclude), a nucleoside analogue, is rapidly phosphorylated to the active intracellular 5'-triphosphate form that inhibits replication of hepatitis B virus (HBV). Oral entecavir is approved in the US, EU and several countries worldwide for the treatment of chronic HBV infection in adults (> or =16 years of age) with evidence of active viral replication and persistently elevated serum ALT and/or AST levels, and/or histological evidence of active disease. In several randomized, double-blind, multicentre trials, oral entecavir was an effective and generally well tolerated treatment in nucleoside-naive and lamivudine-refractory adult patients with chronic HBV infection, irrespective of whether patients were hepatitis B e antigen (HBeAg)-positive or -negative. Furthermore, it was more efficacious, associated with a lower risk of resistance, and more cost effective than lamivudine in these patient populations, with both drugs having a similar tolerability profile. In the EARLY trial, entecavir was significantly more effective than and as well tolerated as adefovir dipivoxil therapy in nucleoside-naive patients. In addition, in a double-blind, multicentre trial, entecavir plus lamivudine-based highly active antiretroviral therapy (HAART) was more effective than placebo plus lamivudine-based HAART in patients co-infected with HBV and HIV. Although the exact position of entecavir relative to other agents, such as tenofovir disoproxil fumarate and adefovir dipivoxil, for the treatment of chronic HBV infection remains to be fully determined, an important aspect in this positioning is the emergence of drug resistance. Hence, entecavir therapy provides a valuable first-line option in nucleoside-naive patients with chronic HBV infection and is a useful alternative in lamivudine-refractory patients.

Entecavir shows limited efficacy in HBeAg-positive hepatitis B patients with a partial virologic response to adefovir therapy

BACKGROUND/AIMS

We investigated the efficacy of entecavir in lamivudine-experienced and -naïve patients with persistently high HBV DNA during adefovir treatment.

METHODS

Fourteen chronic hepatitis B patients (57% lamivudine-experienced) with a viral load above 5log(10)copies/mL after 12months of adefovir therapy and thereafter were treated with entecavir 1mg daily.

RESULTS

During a median follow-up of 15months (range: 8-23months) one of six lamivudine-naïve and none of the eight lamivudine-experienced patients achieved undetectable HBV DNA (<373copies/mL). HBeAg loss occurred in none of the subjects. Two lamivudine-experienced patients demonstrated the rtM204I mutation; no other entecavir-resistant substitutions were detected (rtI169, rtT184, rtS202, and rtM250). Two of three patients with genotypic adefovir resistance at baseline demonstrated a rapid virologic response to entecavir, but undetectable HBV DNA was not achieved. To attain a better antiviral response the dosage of entecavir was increased to 2mg daily in two patients, resulting in further viral load decline for both of them.

CONCLUSIONS

Entecavir monotherapy dosed at 1mg resulted in a slow reduction of viral load in both lamivudine-experienced and -naïve patients with persistently high HBV DNA during adefovir therapy. Increasing the dosage of entecavir led to further HBV DNA decline.

A sensitive method for the determination of entecavir at picogram per milliliter level in human plasma by solid phase extraction and high-pH LC-MS/MS

Entecavir is a guanine nucleoside analogue used in the treatment of hepatitis B virus (HBV) infection. In this paper, we describe an LC-MS/MS method that was developed and validated for the quantitation of entecavir in human EDTA plasma with both high sensitivity (lower limit of quantitation (LLOQ) of 5 pg/mL) and a wide concentration range (5000-fold) intended for low dose ascending clinical studies. High enrichment was achieved by taking advantage of the excellent loading capacity and reproducibility of Oasis HLB 96-well solid phase extraction plate, which allowed 1 mL of plasma samples to be processed in two equal sequential loading steps. Lobucavir, a structural analogue, was used as the internal standard. A filtration step following the reconstitution proved to be vital for the method robustness. The analyte and internal standard were separated on an Xterra MS C18 column with a gradient elution and high-pH mobile phases. Analytes were detected by positive ion electrospray tandem mass spectrometry. The high-pH mobile phase provided both excellent analyte on-column retention and peak shape, leading to the desired sensitivity. Validation results show good intra-assay (12.3%CV) and inter-assay (3.1%CV) precisions, and good assay accuracy (+/-7.6%Dev). Recovery was high (approximately 80%), however, the large volume of plasma used did result in a considerable matrix effect (approximately 0.45) which was well compensated by the analog internal standard. The method was applied to sample analysis of a Phase I clinical study.

Lack of an effect of human immunodeficiency virus coinfection on the pharmacokinetics of entecavir in hepatitis B virus-infected patients

Entecavir is a guanosine nucleoside analogue approved for the treatment of chronic hepatitis B virus (HBV) infection. The impact of human immunodeficiency virus (HIV) coinfection on the pharmacokinetics (PK) of entecavir was examined by nonlinear mixed-effects modeling. Plasma concentration data from HIV- and HBV-coinfected patients were analyzed in conjunction with data from HBV-monoinfected patients, and HIV coinfection was tested as a covariate on oral clearance (CL/F). The estimated population averages of intercompartmental clearance and the volumes of distribution in the central and peripheral compartments obtained with a 1-mg dose were 34.2 liters/h (interindividual variability, 30.2%), 115 liters (interindividual variability, 39.2%), and 1,830 liters (interindividual variability, 74%), respectively. CL/F was found to be a function of creatinine clearance, but HIV confection did not show any effect on CL/F. The geometric mean (GM) of individual Bayesian estimates of the steady-state area under the concentration-time curve following 1-mg daily doses were 39.3 and 38.8 ng x h/ml in HIV- and HBV-coinfected and HBV-monoinfected patients, respectively. The adjusted GM ratio (1.01; 90% confidence interval, 0.91 to 1.12) was within the bioequivalence criteria boundary (0.80 to 1.25). In conclusion, the proposed model adequately described the entecavir PK in HBV- and HIV-coinfected patients and HBV-monoinfected patients, and the entecavir exposures were comparable in the two patient populations.

New drugs for chronic hepatitis B: a review

Three nucleotide/nucleoside analogs are used for chronic hepatitis B (HBV): lamivudine, adefovir dipivoxil, and entecavir. Lamivudine and adefovir are advantageous for oral administration and safety but induce a sustained response after withdrawal of therapy in only a minority of patients. Thus, the treatment should be given in trials in a majority of patients for a long period of time. In addition, the long-term efficacy of lamivudine is limited by the frequent emergence of drug-resistant HBV mutants. Adefovir is associated with a low frequency of resistance, but its antiviral effect is not optimal. Entecavir, a cyclopentyl guanosine analog, is a potent inhibitor of HBV-DNA polymerase and it inhibits both priming and elongation steps of viral DNA replication. In phase II and III clinical trials, entecavir was found to be superior to lamivudine for all primary end points evaluated in both nucleoside-naive and lamivudine-resistant patients, and it was effective in both HBeAg-positive and HBeAg-negative nucleoside-naive patients. Only one trial has shown cases of viral resistance to this drug. The approved dosage in treatment-naive patients is 0.5 mg per day orally, whereas in patients who have failed lamivudine therapy or who are known to harbor lamivudine-resistant mutants, the approved dosage is 1.0 mg per day. Recent preliminary results show that clevudine, telbivudine, and emtricitabine may be potent analogs available for the treatment of HBV. Further studies are being conducted to assess the long-term efficacy and safety of these drugs.

Entecavir for chronic hepatitis B: a review

Three nucleotide/nucleoside analogs are currently used for the treatment of chronic hepatitis B: lamivudine, adefovir dipivoxil, and entecavir. Lamivudine and adefovir are beneficial for oral administration and safety, but only a few of the patients treated experience a sustained response after therapy withdrawal. Entecavir, a cyclopentyl guanosine analog, is a potent inhibitor of chronic hepatitis B virus DNA polymerase, inhibiting both the priming and elongation steps of viral DNA replication. In phase II and phase III clinical trials, entecavir was found to be superior to lamivudine for all primary end points evaluated in both nucleoside-naive and lamivudine-resistant patients as well as being effective in both HBeAg-positive and HBeAg-negative nucleoside-naive patients. Only one trial has shown evidence of cases of viral resistance to this drug. The approved dosage in treatment-naive patients is 0.5 mg per day orally, whereas in patients who have failed lamivudine therapy or are known to harbor lamivudine-resistant mutants, the approved dosage is 1.0 mg per day.

Entecavir exhibits inhibitory activity against human immunodeficiency virus under conditions of reduced viral challenge

Entecavir (ETV) was developed for the treatment of chronic hepatitis B virus (HBV) infection and is globally approved for that indication. Initial preclinical studies indicated that ETV had no significant activity against human immunodeficiency virus type 1 (HIV-1) in cultured cell lines at physiologically relevant ETV concentrations, using traditional anti-HIV assays. In response to recent clinical observations of anti-HIV activity of ETV in HIV/HBV-coinfected patients not receiving highly active antiretroviral therapy (HAART), additional investigative studies were conducted to expand upon earlier results. An extended panel of HIV-1 laboratory and clinical strains and cell types was tested against ETV, along with a comparison of assay methodologies and resistance profiling. These latest studies confirmed that ETV has only weak activity against HIV, using established assay systems. However, a >100-fold enhancement of antiviral activity (equivalent to the antiviral activity of lamivudine) could be obtained when assay conditions were modified to reduce the initial viral challenge. Also, the selection of a M184I virus variant during the passage of HIV-1 at high concentrations of ETV confirmed that ETV can exert inhibitory pressure on the virus. These findings may have a significant impact on how future assays are performed with compounds to be used in patients infected with HIV. These results support the recommendation that ETV therapy should be administered in concert with HAART for HIV/HBV-coinfected patients.

Entecavir is a potent anti-HBV drug superior to lamivudine: experience from clinical trials in China

Infection with the hepatitis B virus (HBV) can result in chronic hepatitis B (CHB) in many patients. Patients with CHB require regular screening and monitoring to facilitate disease surveillance and to determine if/when treatment is indicated. The current goal of CHB treatment is sustained viral suppression with the aim of reducing or preventing hepatic injury and disease progression. Effective anti-HBV therapy is now available that can suppress, but not eradicate, HBV replication. Among the currently licensed and approved anti-HBV nucleos(t)ides, entecavir demonstrates a potent anti-HBV activity and a low rate of emergence of drug resistance, with good safety and tolerability profiles. These excellent pharmacological characteristics were assessed both in large international clinical trials and in separate studies in China. This article presents results from Phase II and Phase III trials involving 876 Chinese patients with CHB. The results of these studies suggest that entecavir should be recommended as a first-line choice among the currently available anti-HBV nucleos(t)ides.