Changing the face of hepatitis C management - the design and development of sofosbuvir

Road to elimination of HCV: Clinical challenges in HCV management

Since its discovery in 1989, the road to a cure for hepatitis C virus (HCV) has been slow, but most patients can now expect to achieve a sustained virological response (SVR). With direct-acting antiviral (DAA) combination therapies such as glecaprevir/pibrentasvir and velpatasvir/sofosbuvir, 98% of patients successfully eradicate the virus, even if previous treatments failed or if resistance-associated substitutions (RASs) are present. Adverse events are rare or mild, and patients with compensated cirrhosis and other co-morbidities are often eligible for treatment. However, a small number of patients fail to eradicate the virus even after retreatment. The cause of failure is mainly due to emergence of NS5A P32 deletion mutants after initial DAA therapy in genotype 1b patients, although the reason is unknown for some patients. Alternative therapies that do not rely on NS5A inhibitors, such as sofosbuvir plus ribavirin, can be attempted in these patients. While scaled-up treatment efforts present a challenge, another problem is that many carriers are unaware of their infection. Long-term damage to the liver becomes irreversible, and patients who are not diagnosed in time can develop liver cancer or liver failure even after eliminating the virus. The long-term costs of treatment of advanced liver disease in undiagnosed patients relative to the immediate costs of DAA therapy should be considered. As no vaccine is yet available, eventual elimination of the virus requires identifying and treating undiagnosed cases and screening of high-risk populations such as injection drug users and men who have sex with men and female sex workers.

Hepatitis C: A Pharmacological Therapeutic Update

(1) Background: Hepatitis C is a high-prevalence disease, representing a global impact health problem. Lately, many changes have been made in treatment guidelines because of the commercialization of second-generation direct-acting antivirals due to their high effectiveness, few side effects and pangenotypic action. We address the pharmacological possibilities available and compare them with the current recommendations of the World Health Organization (WHO). (2) Methods: The search for articles was made through the PubMed database using different search strategies and we consulted technical data sheets of the treatments that have been included in the study. (3) Results: Combinations of “glecaprevir/pibrentasvir”, “sofosbuvir/velpatasvir” and “sofosbuvir/velpatasvir/voxilaprevir” have been recently incorporated. Phase II studies have shown that they are safe and effective therapies with very comfortable posologies and easy therapeutic adherence; furthermore, they suppose shorter treatment duration. Subsequently, phase III studies have shown they were effective for previously treated or compensated cirrhotic patients that previously had more complex treatment regimens. (4) Conclusions: These results suppose a simplification in Hepatitis C therapeutic approach, and open new study possibilities.

Pharmacokinetic interaction between atorvastatin and fixed-dose combination of sofosbuvir/ledipasvir in healthy male Egyptian volunteers

PURPOSE

Comorbid conditions of heart and liver disorders added to HCV-induced hepatic steatosis make co-administration of statins, and direct-acting antivirals is common in clinical practice. This study aimed to evaluate the pharmacokinetic interaction of atorvastatin and fixed-dose combination of sofosbuvir/ledipasvir "FDCSL" with rationalization to the underlying mechanism.

METHODS

A randomized, three-phase crossover study that involves 12 healthy volunteers was performed. Participants received a single-dose of atorvastatin 80 mg alone, atorvastatin 80-mg plus tablets containing 400/90 mg FDCSL, or tablets containing 400/90 mg FDCSL alone. Plasma samples were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for atorvastatin, sofosbuvir, ledipasvir, and sofosbuvir metabolite "GS-331007," and their pharmacokinetics parameters were determined.

RESULTS

Compared to atorvastatin alone, the administration of FDCSL caused a significant increase in both areas under the concentration-time curve from time zero to infinity (AUC_0-∞) and maximum plasma concentration (C_max) of atorvastatin by 65.5% and 156.0%, respectively. Also, atorvastatin caused a significant increase in the AUC_0-∞ and C_max of sofosbuvir by 32.0% and 11.0%, respectively. Similarly, AUC_0-∞ and C_max of sofosbuvir metabolite significantly increased by 84.0% and 74.0%, respectively. However, ledipasvir AUC_0-∞ showed no significant change after atorvastatin intake. The elimination rate in all drugs revealed no significant changes.

CONCLUSION

After concurrent administration of FDCSL with atorvastatin, the AUC_0-∞ of both atorvastatin and sofosbuvir were increased. Caution should be taken with close monitoring for possible side effects after co-administration of atorvastatin and FDCSL in clinical practice.

Coronavirus RNA Proofreading: Molecular Basis and Therapeutic Targeting

The coronavirus disease 2019 (COVID-19) that is wreaking havoc on worldwide public health and economies has heightened awareness about the lack of effective antiviral treatments for human coronaviruses (CoVs). Many current antivirals, notably nucleoside analogs (NAs), exert their effect by incorporation into viral genomes and subsequent disruption of viral replication and fidelity. The development of anti-CoV drugs has long been hindered by the capacity of CoVs to proofread and remove mismatched nucleotides during genome replication and transcription. Here, we review the molecular basis of the CoV proofreading complex and evaluate its potential as a drug target. We also consider existing nucleoside analogs and novel genomic techniques as potential anti-CoV therapeutics that could be used individually or in combination to target the proofreading mechanism.

COVID-19 Therapeutic Options Under Investigation

Since its emergence in China in December 2019, COVID-19 has quickly spread around the globe causing a pandemic. Vaccination or the development of herd immunity seems the only way to slow down the spread of the virus; however, both are not achievable in the near future. Therefore, effective treatments to mitigate the burden of this pandemic and reduce mortality rates are urgently needed. Preclinical and clinical studies of potential antiviral and immunomodulatory compounds and molecules to identify safe and efficacious therapeutics for COVID-19 are ongoing. Two compounds, remdesivir, and dexamethasone have been so far shown to reduce COVID-19-associated death. Here, we provide a review of the potential therapeutic agents being considered for the treatment and management of COVID-19 patients.

Full-dose sofosbuvir plus low-dose ribavirin for hepatitis C virus genotype 2-infected patients on hemodialysis

BACKGROUND/AIMS

New direct-acting antivirals have shown surprising success in the treatment of hepatitis C, not only in the general population, but also in difficult-to-treat cohorts. However, there is still limited data regarding direct-acting antivirals, including sofosbuvir (SOF), in the context of hemodialysis. The aim of this study was to investigate the safety and outcome of administering full-dose SOF (400 mg/day) plus low-dose ribavirin (RBV, 100 to 200 mg/day) in hemodialysis patients with hepatitis C virus (HCV) genotype 2 (GT2) infection.

METHODS

Patients with chronic HCV GT2 infection and end-stage renal disease on maintenance hemodialysis treated with full-dose SOF plus low-dose RBV were retrospectively identified from a database of patients with HCV GT2 who were treated in Konkuk University Chungju Hospital between February 2017 and February 2018. Medical records were reviewed for demographics, medical history, laboratory data, and radiologic and electrocardiographic findings.

RESULTS

All nine patients completed a full course of 12 weeks of treatment with a full-dose SOF plus low-dose RBV regimen. Two had compensated cirrhosis. Seven patients were treatment-naïve, and two had a relapse following previous interferon-based therapy. All patients had a sustained viral response at 12 weeks post-treatment. There was no discontinuation of treatment because of side effects.

CONCLUSION

In hemodialysis patients with HCV GT2 infection, the full-dose SOF plus low-dose RBV regimen appears to be safe and well tolerated, and yields high rates of sustained virologic response.

Direct-acting Antivirals for the Treatment of Kidney Transplant Patients With Chronic Hepatitis C Virus Infection in Spain: A Long-term Prospective Observational Study

Background

Direct-acting antivirals (DAA) allow effective and safe eradication of hepatitis C virus (HCV) in most patients. There are limited data on the long-term effects of all-oral, interferon-free DAA combination therapies in kidney transplant (KT) patients infected with HCV. Here we evaluated the long-term tolerability, efficacy, and safety of DAA combination therapies in KT patients with chronic HCV infection.

Methods

Clinical data from KT patients treated with DAA were collected before, during, and after the treatment, including viral response, immunosuppression regimens, and kidney and liver function.

Results

Patients (N = 226) were mostly male (65.9%) aged 56.1 ± 10.9 years, with a median time from KT to initiation of DAA therapy of 12.7 years and HCV genotype 1b (64.6%). Most patients were treated with sofosbuvir-based therapies. Rapid virological response at 1 month was achieved by 89.4% of the patients and sustained virological response by week 12 by 98.1%. Liver function improved significantly after DAA treatment. Tacrolimus dosage increased 37% from the beginning of treatment (2.5 ± 1.7 mg/d) to 1 year after the start of DAA treatment (3.4 ± 1.9 mg/d, P < 0.001). Median follow-up was 37.0 months (interquartile range, 28.4-41.9) and death-censored graft survival was 91.1%. Adverse events resulting from DAA treatment, especially anemia, were reported for 31.0% of the patients.

Conclusions

Chronic HCV infection can be treated efficiently and safely with DAA therapy in KT patients. Most patients retained stable kidney function and improved liver function. Tacrolimus dose had to be increased in most patients, potentially as a result of better liver function.

A long acting nanoformulated lamivudine ProTide

A long acting (LA) hydrophobic and lipophilic lamivudine (3TC) was created as a phosphoramidate pronucleotide (designated M23TC). M23TC improved intracellular delivery of active triphosphate metabolites and enhanced antiretroviral and pharmacokinetic (PK) profiles over the native drug. A single treatment of human monocyte derived macrophages (MDM) with nanoformulated M23TC (NM23TC) improved drug uptake, retention, intracellular 3TC triphosphates and antiretroviral activities in MDM and CD4⁺ T cells. PK tests of NM23TC administered to Sprague Dawley rats demonstrated sustained prodrug and drug triphosphate levels in blood and tissues for 30 days. The development of NM23TC remains a substantive step forward in producing LA slow effective release antiretrovirals for future clinical translation.

Non-Coding RNAs and Hepatitis C Virus-Induced Hepatocellular Carcinoma

Hepatitis C virus (HCV) infection is a worldwide health problem and is one of the main causes of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma (HCC). Despite recent improvements, effective treatments for HCC are still missing and new tools for early detection are needed. Non-coding RNAs (ncRNAs) have emerged as important regulators of gene expression and key players in human carcinogenesis, including HCC. Aberrant expression of ncRNAs is associated with HCC metastasis, invasion, dissemination, and recurrence. This review will focus on the recent advances in ncRNA expression profiles, their dysregulation in HCV-related HCC, and the clinical perspective of ncRNA signatures for the early detection of HCC.

Hepatitis C and renal transplantation in era of new antiviral agents

Data from World Health Organization estimates that the hepatitis C virus (HCV) prevalence is 3% and approximately 71 million persons are infected worldwide. HCV infection is particularly frequent among patients affected by renal diseases and among those in dialysis treatment. In addition to produce a higher rate of any cause of death, HCV in renal patients and in renal transplanted patients produce a deterioration of liver disease and is a recognized cause of transplant glomerulopathy, new onset diabetes mellitus and lymphoproliferative disorders. Treatment of HCV infection with interferon alpha and/or ribavirin had a poor efficacy. The treatment was toxic, expensive and with limited efficacy. In the post-transplant period was also cause of severe humoral rejection. In this review we have highlighted the new direct antiviral agents that have revolutionized the treatment of HCV both in the general population and in the renal patients. Patients on dialysis or with low glomerular filtration rate were particularly resistant to the old therapies, while the direct antiviral agents allowed achieving a sustained viral response in 90%-100% of patients with a short period of treatment. This fact to date allows HCV patients to enter the waiting list for transplantation easier than before. These new agents may be also used in renal transplant patients HCV-positive without relevant clinical risks and achieving a sustained viral response in almost all patients. New drug appears in the pipeline with increased profile of efficacy and safety. These drugs are now the object of several phases II, III clinical trials.

Impact of sustained virologic response on chronic kidney disease progression in hepatitis C

AIM

To determine how sustained virological response at 12 wk (SVR12) with direct acting antivirals (DAAs) for the treatment of hepatitis C virus (HCV) infection affects chronic kidney disease (CKD) progression.

METHODS

A retrospective analysis was performed in patients aged ≥ 18 years treated for HCV with DAAs at the VA Greater Los Angeles Healthcare System from 2014-2016. The treatment group was compared to patients with HCV from 2011-2013 who did not undergo HCV treatment, prior to the introduction of DAAs; the control group was matched to the study group in terms of age, gender, and ethnicity. Analysis of variance and co-variance was performed to compare means between SVR12 subgroups adjusting for co-variates.

RESULTS

Five hundred and twenty-three patients were evaluated. When comparing the rate of change in estimated glomerular filtration rate (eGFR) one-year after HCV treatment to one-year before treatment, patients who achieved SVR12 had a decline in GFR of 3.1 mL/min ± 0.75 mL/min per 1.73 m² compared to a decline in eGFR of 11.0 mL/min ± 2.81 mL/min per 1.73 m² in patients who did not achieve SVR12 (P = 0.002). There were no significant clinical differences between patients who achieved SVR12 compared to those who did not in terms of cirrhosis, treatment course, treatment experience, CKD stage prior to treatment, diuretic use or other co-morbidities. The decline in eGFR in those with untreated HCV over 2 years was 2.8 mL/min ± 1.0 mL/min per 1.73 m², which was not significantly different from the eGFR decline noted in HCV-treated patients who achieved SVR12 (P = 0.43).

CONCLUSION

Patients who achieve SVR12 have a lesser decline in renal function, but viral eradication in itself may not be associated improvement in renal disease progression.

New Viral and Immunological Targets for Hepatitis B Treatment and Cure: A Review

Although current therapies can be successful at suppressing hepatitis B viral load, long-term viral cure is not within reach. Subsequent strategies combining pegylated interferon alfa with nucleoside/nucleotide analogues have not resulted in any major paradigm shift. An improved understanding of the hepatitis B virus (HBV) lifec ycle and virus-induced immune dysregulation has, however, revealed many potential therapeutic targets, and there are hopes that treatment of hepatitis B could soon be revolutionized. This review summarizes the current developments in HBV therapeutics-both virus directed and host directed.

Safety and efficacy of current direct-acting antiviral regimens in kidney and liver transplant recipients with hepatitis C: Results from the HCV-TARGET study

Data outside of clinical trials with direct-acting antiviral regimens with or without ribavirin as treatment of chronic hepatitis C virus in solid organ transplant recipients are limited. Liver transplant (LT), kidney transplant (KT), and dual liver kidney (DLK) transplant recipients from the Hepatitis C Therapeutic Registry and Research Network database, a multicenter, longitudinal clinical care treatment cohort, treated with direct-acting antiviral regimens between January 1, 2014, and February 15, 2016, were included to assess safety and efficacy. Included were 443 posttransplant patients (KT = 60, LT = 347, DLK = 36); 42% had cirrhosis, and 54% had failed prior antiviral therapy. Most had genotype (GT) 1 (87% with 52% GT1a, 27% GT1b, and 8% GT1 no subtype) and were treated with sofosbuvir (SOF)/ledipasvir ± ribavirin (85%) followed by SOF + daclatasvir ± ribavirin (9%) and ombitasvir/paritaprevir/ritonavir + dasabuvir ± ribavirin (6%). Rates of sustained virologic response (SVR) at 12 weeks were available on 412 patients, and 395 patients (95.9%) achieved SVR at 12 weeks: 96.6%, 94.5%, and 90.9% among LT, KT, and DLK transplant recipients, respectively. Ribavirin did not influence SVR rates and was more often used in those with higher BMI, higher estimated glomerular filtration rate and lower creatinine. Female gender, baseline albumin ≥3.5 g/dL, baseline total bilirubin ≤1.2 mg/dL, absence of cirrhosis, and hepatic decompensation predicted SVR at 12 weeks. Six episodes of acute rejection (n = 2 KT, 4 LT) occurred, during hepatitis C virus treatment in 4 and after cessation of treatment in 2.

CONCLUSION

In a large prospective observational cohort study, direct-acting antiviral therapy with SOF/ledipasvir, ombitasvir/paritaprevir/ritonavir + dasabuvir, and SOF plus daclatasvir was efficacious and safe in LT, KT, and DLK transplant recipients; ribavirin did not influence SVR, and graft rejection was rare. (Hepatology 2017;66:1090-1101).

Continuum of hepatitis C care in France: A 20-year cohort study

Background

Hepatitis C virus (HCV)-infected patients require a specific continuum of care (CoC) from HCV screening to treatment. We assessed CoC of HCV-infected patients in a longitudinal study.

Methods

We established a cohort of subjects undergoing HCV screening (high alanine aminotransferase levels or risk factors) during preventive consultations at a French regional medical center from 1993 to 2013. Patients were considered to be HCV-infected if HCV RNA was detected in their serum. CoC was assessed as described by Viner et al. (Hepatology 2015): Stage 1, HCV screening; Stage 2, HCV RNA testing; Stage 3, continuing care; Stage 4, antiviral treatment. Cox multivariate analysis was performed to identify factors favoring CoC, defined as at least one course of antiviral treatment.

Results

In total, 12,993 HCV tests were performed and 478 outpatients were found to be HCV-seropositive. We included 417 seropositive patients, after excluding false positives and patients lost to follow-up. The baseline characteristics of the patients were: sex ratio (M/F) 1.4; mean age 38.5 years; intravenous drug use (IDU) in 55%; and 28% in unstable social situations, estimated by the EPICES deprivation score. Antiviral treatment was initiated for 179 (42.9%) of the 379 (90.9%) patients attending specialist consultations. CoC was associated with screening after 1997 (HR 2.0, 95%CI 1.4–2.9), age > 45 years (HR 1.5, 95%CI 1.02–2.3), patient acceptance of care (HR 9.3, 95%CI 5.4–16.10), specialist motivation for treatment (HR 10.9, 95%CI 7.4–16.0), and absence of cancer (HR 6.7, 95%CI 1.6–27.9). Other comorbid conditions, such as depression and IDU, were not associated with CoC.

Conclusions

Our 20-year cohort study reveals the real-life continuum of care for HCV-infected patients in France. The number of patients involved in HCV care after positive testing was substantial due to the organization of healthcare in France. An improved CoC along with new direct-acting antivirals should help to decrease chronic HCV infection.

Patch-Clamp Study of Hepatitis C p7 Channels Reveals Genotype-Specific Sensitivity to Inhibitors

Hepatitis C is a major worldwide disease and health hazard, affecting ∼3% of the world population. The p7 protein of hepatitis C virus (HCV) is an intracellular ion channel and pH regulator that is involved in the viral replication cycle. It is targeted by various classical ion channel blockers. Here, we generated p7 constructs corresponding to HCV genotypes 1a, 2a, 3a, and 4a for recombinant expression in HEK293 cells, and studied p7 channels using patch-clamp recording techniques. The pH50 values for recombinant p7 channels were between 6.0 and 6.5, as expected for proton-activated channels, and current-voltage dependence did not show any differences between genotypes. Inhibition of p7-mediated currents by amantadine, however, exhibited significant, genotype-specific variation. The IC50 values of p7-1a and p7-4a were 0.7 ± 0.1 nM and 3.2 ± 1.2 nM, whereas p7-2a and p7-3a had 50- to 1000-fold lower sensitivity, with IC50 values of 2402 ± 334 nM and 344 ± 64 nM, respectively. The IC50 values for rimantadine were low across all genotypes, ranging from 0.7 ± 0.1 nM, 1.6 ± 0.6 nM, and 3.0 ± 0.8 nM for p7-1a, p7-3a, and p7-4a, respectively, to 24 ± 4 nM for p7-2a. Results from patch-clamp recordings agreed well with cellular assays of p7 activity, namely, measurements of intracellular pH and hemadsorption assays, which confirmed the much reduced amantadine sensitivity of genotypes 2a and 3a. Thus, our results establish patch-clamp studies of recombinant viroporins as a valid analytical tool that can provide quantitative information about viroporin channel properties, complementing established techniques.

Chronic hepatitis C and chronic kidney disease: Advances, limitations and unchartered territories

Over the past few years, treatment options for chronic hepatitis C virus (HCV) infection have evolved dramatically. The current approved interferon-free direct-acting antiviral (DAA) regimens have been shown to be safe and effective with sustained virologic response (SVR) rates of >90% in most patients. Unique issues yet remain such as the challenges in patients with impaired renal function or decompensated cirrhosis. Patients with stages 4-5 chronic kidney disease (CKD) have a higher prevalence of HCV infection compared with the general population. Chronic HCV in those on dialysis and in kidney transplant recipients is associated with higher morbidity and mortality than uninfected patients. The HCV-infected population is also at risk of developing extrahepatic manifestations associated with altered immune system function and chronic inflammation with cryoglobulinaemic vasculitis being the most common of these manifestations. Therefore, patients with CKD stages 4-5 have to be considered priority patients for HCV therapy. New antiviral therapies have the potential to improve outcomes in this vulnerable patient population, including those on haemodialysis. Recently published studies conducted in kidney transplant recipients have demonstrated successful outcomes. It is thus essential that we carefully select the most appropriate DAA regimen and the best time for treatment in the context of kidney transplantation or cryoglobulinaemic vasculitis. While sofosbuvir, the only approved nucleotide NS5B inhibitor, has been the backbone of most pangenotypic therapeutic regimens, it has a limitation in those with advanced kidney disease. The currently approved regimens for those with stage 4/5 CKD, while effective, have challenges in that they apply to genotype 1/4 and may require RBV for genotype 1a. Globally, genotype 3 is a common infection, and thus, this group with CKD presents a huge unmet need for effective therapies. As therapy of HCV in renal transplant recipients has been highly successful, it provides an opportunity to expand the use of HCV-infected organs in solid organ transplantation.

New-Onset Diabetes Mellitus With Exposure to Ledipasvir and Sofosbuvir

The combination therapy of ledipasvir/sofosbuvir was approved by the Food and Drug Administration in 2014 for the treatment of chronic hepatitis C. Although hyperglycemia is not well known to occur with its use, we present 2 cases of new-onset diabetes mellitus and a review of the literature suggesting an adverse event association. In the first patient with HIV, we postulate that ledipasvir/sofosbuvir increased the levels of tenofovir and thereby potentiated hyperglycemia. In the second case of a patient with prediabetes, ledipasvir/sofosbuvir appeared to increase insulin resistance. A literature review further supported an association of hyperglycemia and the use of ledipasvir/sofosbuvir. Hence, clinicians should be cautious about worsening of glucose intolerance, and more studies are warranted to explore the underlying mechanism.

Hepatitis C virus infection: Are there still specific problems with genotype 3?

Hepatitis C virus (HCV) infection is one of the most common causes of chronic liver disease and the main indication for liver transplantation worldwide. As promising specific treatments have been introduced for genotype 1, clinicians and researchers are now focusing on patients infected by non-genotype 1 HCV, particularly genotype 3. Indeed, in the golden era of direct-acting antiviral drugs, genotype 3 infections are no longer considered as easy to treat and are associated with higher risk of developing severe liver injuries, such as cirrhosis and hepatocellular carcinoma. Moreover, HCV genotype 3 accounts for 40% of all HCV infections in Asia and is the most frequent genotype among HCV-positive injecting drug users in several countries. Here, we review recent data on HCV genotype 3 infection/treatment, including clinical aspects and the underlying genotype-specific molecular mechanisms.

Nucleobase but not Sugar Fidelity is Maintained in the Sabin I RNA-Dependent RNA Polymerase

The Sabin I poliovirus live, attenuated vaccine strain encodes for four amino acid changes (i.e., D53N, Y73H, K250E, and T362I) in the RNA-dependent RNA polymerase (RdRp). We have previously shown that the T362I substitution leads to a lower fidelity RdRp, and viruses encoding this variant are attenuated in a mouse model of poliovirus. Given these results, it was surprising that the nucleotide incorporation rate and nucleobase fidelity of the Sabin I RdRp is similar to that of wild-type enzyme, although the Sabin I RdRp is less selective against nucleotides with modified sugar groups. We suggest that the other Sabin amino acid changes (i.e., D53N, Y73H, K250E) help to re-establish nucleotide incorporation rates and nucleotide discrimination near wild-type levels, which may be a requirement for the propagation of the virus and its efficacy as a vaccine strain. These results also suggest that the nucleobase fidelity of the Sabin I RdRp likely does not contribute to viral attenuation.

HCV Drug Resistance Challenges in Japan: The Role of Pre-Existing Variants and Emerging Resistant Strains in Direct Acting Antiviral Therapy

Sustained virological response (SVR) rates have increased dramatically following the approval of direct acting antiviral (DAA) therapies. While individual DAAs have a low barrier to resistance, most patients can be successfully treated using DAA combination therapy. However, DAAs are vulnerable to drug resistance, and resistance-associated variants (RAVs) may occur naturally prior to DAA therapy or may emerge following drug exposure. While most RAVs are quickly lost in the absence of DAAs, compensatory mutations may reinforce fitness. However, the presence of RAVs does not necessarily preclude successful treatment. Although developments in hepatitis C virus (HCV) therapy in Asia have largely paralleled those in the United States, Japan’s July 2014 approval of asunaprevir plus daclatasvir combination therapy as the first all-oral interferon-free therapy was not repeated in the United States. Instead, two different combination therapies were approved: sofosbuvir/ledipasvir and paritaprevir/ritonavir/ombitasvir/dasabuvir. This divergence in treatment approaches may lead to differences in resistance challenges faced by Japan and the US. However, the recent approval of sofosbuvir plus ledipasvir in Japan and the recent submissions of petitions for approval of paritaprevir/ritonavir plus ombitasvir suggest a trend towards a new consensus on emerging DAA regimens.