Pooled model-based approach to compare the pharmacokinetics of entecavir between Japanese and non-Japanese chronic hepatitis B patients

Revisiting HBV resistance to entecavir with a phenotypic approach

Treatment adaptation after hepatitis B virus (HBV) treatment failure relies on genotypic resistance testing. However, the results of such tests are not always consistent with treatment response. These discrepancies may be due to differences in resistance levels between isolates with the same genotypic resistance testing profiles. We explored this hypothesis by investigating six cases of entecavir treatment failure with an integrative strategy combining genotypic and phenotypic resistance testing, medical record review and therapeutic drug monitoring. Among isolates with genotypic reduced susceptibility to entecavir, one displayed a higher level of resistance to entecavir (mean fold change in entecavir IC₅₀ of 1 508 ± 531 vs. 318 ± 53, p = 0.008). This isolate harbored a substitution (rt250L) at a position reported to be associated with resistance (rt250V). Reversion to wild-type amino acid at this position partially restored susceptibility to entecavir, confirming that the rt250L mutation was responsible for the high level of resistance to entecavir. This is the first description of entecavir treatment failure associated with selection of the rt250L mutation without other entecavir resistance mutations. One isolate with genotypic resistance to entecavir, harboring the rt173L mutation, displayed a lower level of resistance than the other, harboring the rt202G mutation (mean fold change of 323 ± 124 vs. 6 036 ± 2 100, p = 0.20). These results suggest that isolates harboring the rt250L mutations should be considered resistant to entecavir, whereas isolates harboring the rt173L mutations should be considered to display reduced susceptibility to entecavir. An integrative approach to antiviral drug resistance in HBV would provide a more accurate assessment of entecavir treatment failures and help to improve the accuracy of genotypic testing algorithms.

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.