Efficacy of Sofosbuvir and Ribavirin for treatment of Hepatitis C Genotype-1 in an Inner City Population: Virus and Host Factors that Predict Relapse

Abstract

Importance

The role of directly acting antiviral agents in an interferon-free regimen for the treatment of chronic Hepatitis C infections needs to be evaluated in different populations.

Objective

To determine the efficacy and safety of sofosbuvir with weight-based or low-dose ribavirin in a population with unfavorable traditional treatment predictors.

Design, Setting, and Patients

Single center, randomized, two-part, open-label phase 2a trial of 60 HCV genotype-1, treatment naive participants were enrolled at the National Institutes of Health, between October 2011 and April 2012.

Intervention

In part 1, ten participants with early-moderate liver fibrosis were treated with 400mg daily of sofosbuvir and weight-based ribavirin (1000mg/daily if ≤ 75kg or 1200mg/daily if >75kg) for 24 weeks. In part 2, 50 participants with all stages of liver fibrosis were randomized 1:1 to receive sofosbuvir with either weight-based or low-dose 600mg daily ribavirin for 24 weeks.

Main Outcome Measures

The primary study end point was the proportion of participants with undetectable HCV viral load 24 weeks after treatment completion (SVR₂₄).

Results

In part 1, 9 (90%, 95% CI, 55% - 100%) achieved SVR_24. In part 2, seven (28%) participants on weight-based ribavirin and ten (40%) participants on low-dose ribavirin relapsed leading to SVR₂₄ rates of 68% (95% CI: 46%-85%) and 48%(95% CI 28%-69%) respectively (p=0.251) A fitted pharmacokinetic-viral kinetic model demonstrated a slower loss rate of infectious virus in relapsers. In bivariable analysis, male gender, advanced liver fibrosis and high baseline HCV RNA were associated with relapse. The regimen was safe and well tolerated with no discontinuations due to adverse events.

Conclusion and Relevance

A combination of sofosbuvir and weight-based ribavirin resulted in a high rate of sustained virologic response in a population traditionally considered difficult to treat. Male gender, advanced liver fibrosis and high baseline HCV RNA were identified as predictors of relapse to this interferon-free, HCV treatment.

Trial Registration

clinicaltrials.gov identifier: NCT01441180.

INTRODUCTION

Chronic infection with hepatitis C virus (HCV) is a major cause of chronic liver disease, end stage liver disease and hepatocellular cancer, and remains the leading indication for liver transplantation in western countries.^1,2 Recent studies show that HCV now surpasses human immunodeficiency virus (HIV) as a cause of death in the United States.³ The HCV epidemic in the U.S is centered in large urban areas among populations with a high prevalence of unfavorable traditional predictors of treatment response. ^1,3,4

The addition of the recently approved directly acting antiviral agents (DAA), telaprevir or boceprevir to pegylated interferon-alpha and ribavirin has resulted in improved SVR rates; however adverse reactions, high pill burdens and drug interactions continue to make treatment challenging with these interferon-based regimens.^5-7 Furthermore host and viral factors including black race, advanced liver fibrosis, IL28B CT/TT genotypes, high baseline HCV viral loads and prior treatment experience remain associated with lower SVR rates with these newer DAA/interferon combinations. ^5,7-9

There have been recent promising studies showing that interferon-free, DAA only regimens can be used successfully to achieve SVR, however populations that have traditionally been associated with poorer treatment outcomes including black race and advanced liver fibrosis have been underrepresented in these studies. ^10-12 One of these studies using sofosbuvir, a selective NS5B inhibitor along with weight-based ribavirin was found to be safe, well-tolerated and highly effective with SVR rates at 12 weeks (SVR₁₂) of 84% in 25 predominantly Caucasian, treatment naive patients with HCV GT-1 from New Zealand.¹¹

This study employed the use of ribavirin, currently a backbone of interferon -based HCV therapy, which is associated with significant adverse events including hemolytic anemia, nausea and teratogenicity. ¹³ Although ribavirin clearly improves SVR rates with interferon-based therapies, ^14,15 the role and requirement for ribavirin in emerging DAA regimens, including optimal dosing have not been established. Hence, we evaluated the safety and efficacy of sofosbuvir as a single DAA administered in combination with weight-based versus low-dose once daily ribavirin for 24 weeks in an inner-city patient population characterized by unfavorable traditional predictors of treatment success. We report the efficacy of this regimen as defined by SVR rates 24 weeks after completion of treatment as well as the host and viral factors associated with treatment relapse.

METHODS

Participants

Sixty participants were enrolled in this single center, two-part, randomized controlled trial performed at the Clinical Research Center of the National Institutes of Health (NIH) in Bethesda from October 2011 through April 2012. Eligible participants were infected with HCV genotype 1 infection, liver biopsy proven chronic disease and naive to HCV treatment. Additional eligibility criteria included seronegativity for HIV and hepatitis B; absolute neutrophil count ≥ 750 cells/mm³; platelet count ≥ 50,000 cells cells/mm³; hemoglobin ≥11 g/dL for women and ≥ 12 g/dL for men. Race/ethnicity was coded to be white, black, or Hispanic using patient self-reported data. Written or oral informed consent was obtained from all participants.

Study Design

The study was performed in two parts. In the first part (proof of concept) ten participants with early to moderate liver fibrosis (Knodell HAI fibrosis score of 0-1) were treated for 24 weeks with 400mg daily of sofosbuvir and weight-based ribavirin (400mg qam, 600mg qpm if < 75kg or 600mg bid if >75kg). In the second part, 50 eligible participants with all stages of fibrosis (including compensated cirrhosis) were randomized using a 1: 1 allocation ratio to receive 400mg daily of sofosbuvir in combination with either weight-based ribavirin (WBR arm) or low-dose 600mg daily ribavirin (LDR arm) for 24 weeks. Participants who experienced treatment failure were offered the current standard of care.

Study Oversight

The study was approved by the institutional review board of the National institutes of Allergy and Infectious diseases (NIAID) and was conducted in compliance with the Good Clinical Practice guidelines, the Declaration of Helsinki and regulatory requirements. The Regulatory Compliance and Human Participants Protection Branch of NIAID served as the study sponsor and medical monitor. An independent safety monitor participated in the interim safety and efficacy analysis. Pharmasset Pharmaceuticals and subsequently Gilead Sciences provided drug and scientific advice.

Efficacy Assessments

Plasma HCV RNA levels were measured using the real time HCV Assay (Abbott), with a lower limit of quantification (LLOQ) of 12 IU per milliliter and a lower limit of detection (LLOD) of 3 IU per milliliter. The Abbott assay was used to measure HCV RNA levels in all participants at all time points. Plasma HCV RNA levels were also measured using the COBAS TaqMan HCV RNA assay, version 1.0 (Roche), with a LLOQ of 43 IU per milliliter and a LLOD of 12 IU per milliliter at specified clinical time points.

Safety Assessments

Adverse events and clinical laboratory results were recorded throughout the study. Adverse events were graded from 1 (mild) to 4 (severe) according to the DAIDS toxicity table (version 1.0). Adherence was determined by pill counts at each visit and patient interviews. A missed dose was defined as any component of the medication regimen not taken on a given day.

Viral Kinetics, Pharmacokinetics, and Pharmacodynamics

Early viral kinetics (VK) pharmacokinetics (PK) and pharmacodynamics (PD) of sofosbuvir and its metabolite GS-331007 were obtained in 25 participants (five in part 1; ten in each arm of part 2). Levels of sofosbuvir and its metabolite GS-331007 in serum were measured at 0, 1, 2, 4, 8, 12, 24, and 36 hours after administration of sofosbuvir and ribavirin using a high performance liquid chromatography – mass spectrometry (LC-MS/MS) bioanalytical technique (QPS, LLC New Jersey).

IL28B Genotyping: rs12979860 SNP

Genotyping of the IL28B single nucleotide polymorphism SNPs rs12979860 has been previously shown to be associated with treatment outcome. ^16,17 Whole blood was collected using PAXgene Blood DNA tubes (Qiagen) and stored at −80C until DNA extraction. DNA was extracted using Paxgene Blood DNA Kit (PreAnalytiX, a Qiagen/BD Company). IL28B genotyping was conducted in a blinded fashion on DNA specimens using the 5′ nuclease assay with IL28B allele specific TaqMan probes (ABI TaqMan allelic discrimination kit) and the ABI7500 Real-Time PCR system (Applied Biosystems, Carlsbad, CA, USA). IL28B genotyping was determined as either favourable (CC genotype) or unfavourable (CT or TT genotypes). ¹⁸

454 Deep sequencing for the detection of S282T NS5B mutation

HCV viral RNA was extracted from plasma using QIAamp Viral RNA Mini (Qiagen) followed by RT-PCR to amplify cDNA. 454 deep sequencing using the Genome Sequencer FLX™ system was then performed in the NS3, 4, 5A, and 5B region to determine the presence of putative resistance-associated variants to GS-7977, such as S282T.

Liver biopsy

All participants had undergone a liver biopsy within 3 years of enrollment and an optional research biopsy was offered post treatment completion (end of treatment + 2 weeks). All histopathological examinations were assessed by a single pathologist in a non-blinded fashion at the time of biopsy and staged according to the Knodell histological activity index (Knodell HAI scoring system). ¹⁹

Clinical End Points

The primary study end point was the proportion of participants with undetectable HCV viral load 24 weeks after treatment completion (SVR₂₄). Secondary efficacy end points included the proportion of participants with undetectable HCV viral load at specified time points during and after treatment. Safety end points included frequency and severity of adverse events, discontinuations due to adverse events and safety laboratory changes.

Modeling Viral Kinetics, Pharmacokinetics and Pharmacodynamics

Pharmacokinetics (PK) of the serum drug level in 20 randomized participants was modeled by a Bateman function using parameters k₁ and k₂ for drug absorption and elimination respectively. For pharmacodynamics (PD), an assumption is made that the effect of blocking viral production depends not directly on the serum drug level but on an intermediate compartment Z defined by

$$\stackrel{.}{Z}\left(t\right)=aC\left(t\right)-aZ\left(t\right)$$

through the Hill function $\epsilon \left(t\right)=\frac{Z{\left(t\right)}^h}{Z{\left(t\right)}^h+I{C}_{50}^h}$

Efficacy depends on drug level, thus varies with time. An estimation of mean and maximum efficacy for the efficacy of antiviral treatment was generated.

The Viral kinetic (VK) model is based on the general model for HCV viral kinetics as previously described. ^20-22

$$\stackrel{.}{V}\left(t\right)=(1-\epsilon )(1-\rho )pI\left(t\right)-cV\left(t\right)$$

$${\stackrel{.}{V}}_{NI}\left(t\right)=(1-\epsilon )\rho pI\left(t\right)-c{V}_{NI}\left(t\right)$$

$$\stackrel{.}{I}\left(t\right)=\beta T\left(t\right)V\left(t\right)+pI\left(t\right)(1-\frac{T\left(t\right)+I\left(t\right)}{T\left(0\right)+I\left(0\right)})-\delta I\left(t\right)$$

$$\stackrel{.}{T}\left(t\right)=\gamma (1-\frac{T\left(t\right)+I\left(t\right)}{T\left(0\right)+I\left(0\right)})$$

Data was fitted by maximum likelihood method accounting for data below the quantitation limits as previously described.²⁹ For the VK model without using a PK-PD approach, only a constant drug effectiveness, infected cell loss rate and baseline viral load were fitted. Loss rate of free virus c was fixed to 5 per day, regeneration rate γ to 3 per day, proliferation p to 3 per day, and ribavirin effect ρ was 60%. Further parameters were obtained from steady state conditions before treatment started. For a full PK-PD approach, the same parameter assumptions were used; additionally, the rate a for the intermediate compartment was log (2)/2 per day and the hill parameter was 1.

Statistical Analysis

The primary interest was in the on-protocol analysis, however the results presented are the intention to treat analysis; ITT (all randomized participants) as these are more readily generalizable. The on-protocol analysis included all participants who received at least 8 weeks of the study drug. A total of 5 participants were taken off study drug due to non-adherence to protocol requirements (3 lost to follow up) but were included in the final ITT analysis (Figure 1). For efficacy analysis, missing data points were deemed a success if immediately preceding and subsequent time points were successful; otherwise data points were termed as failures. In participants with missing data due to premature discontinuations, the subjects were considered failures onwards from point of discontinuation. Comparisons between randomized groups were carried out using the nonparametric Wilcoxon rank sum test for continuous outcomes and Fisher’s exact test for binary outcomes. A bivariable logistic regression model of baseline characteristics was used to identify important predictors of relapse. A multivariable model was found to be unstable even with the exact logistic regression model. All p values were two-tailed, and were considered significant only when lower than 0.05.Analysis was performed using PRIZM 8.0, SAS, STAT-CRUNCH, and S-Plus 8.0.

Figure 1A. Enrollment and treatment outcomes (ITT analysis).

*SVR rates based on all randomized participants (ITT analysis) † cumulative relapsers.

This analysis includes all participants who were taken off study drug/lost to follow up.

part 1: One patient at week 3 was taken off due to non-adherence and lost to follow up

part 2: One patient on weight based RBV: self discontinued at week 3 and lost to follow up.

Three patients on low dose RBV (1 lost to follow up at week 8, 2 participants taken off due to non-adherence at week 8 and remain in follow up).

Figure 1B Treatment response in all randomized subjects (ITT analysis)

In the WBR arm: relapses were as follows: 3 participants 2 weeks after treatment; 3 participants at 4 weeks after treatment while the last patient was 8 weeks after treatment. In the LDR arm: relapses were as follows: 7 participants at 2 weeks after treatment; 1 subject at 4 weeks after treatment, 1 subject at 8 weeks after treatment and 1 was detectable 12 weeks after treatment. Roche assay was used for these time points. LOQ: Level of quantification; SVR: Sustained virologic response.

RESULTS

Seventy-nine participants were screened and 60 were enrolled in this study (Figure 1). All results including treatment response and safety in the ten non-randomized participants (proof of concept) are shown as supplemental data (eTable 1, eTable 2).

BASELINE CHARACTERISTICS OF PARTICIPANTS

Baseline characteristics were similar among treatment groups in the study (Table 1). Participants were predominantly black (83%) male (66%), obese (48%), IL28 CT/TT genotype (81%), GT-1a (70%), had advanced liver disease (23%) and high baseline HCV RNA levels (62%).

Table 1.

Baseline Demographics of Study Participants

Characteristics	Randomized Part		Part 1
	Sofosbuvir + weight-based RBV N=25	Sofosbuvir + low-dose RBV N=25	Sofosbuvir + weight-based RBV N=10
Median age (IQR)	54(51,56)	55 (48,59)	54 (50,57)
Male gender – no (%)	19 (76)	14 (56)	4 (40)
Median body mass index –(IQR)	28 (25,31)	30 (27,37)	26 (26,34)
BMI ≥ 30 – no (%)	12 (48)	14 (56)	3 (30)
Race or ethnicity+ − no (%)
White	5 (20)	2 (8)	1 (10)
Black	18 (72)	23 (92)	9 (90)
Other	2 (8)	0	0
IL28B genotype – no (%)
CC	4 (16)	4 (16)	3 (33)
CT/TT	21 (84)	21 (84)	6 (67)
Knodell HAI Fibrosis – no (%)
0 -1	19 (76)	18 (72)	9 (90)
3 - 4	6 (24)	7 (28)	1 (10)
HCV genotype 1 subtype – no (%)
1a	20 (80)	16 (64)	6 (60)
1b	5 (20%)	9 (36)	4 (4)
Median baseline HCV RNA −log10IU/ml (IQR)	6.2(5.4,6.4)	6.1 (5.5,6.3)	6.8 (6, 7.1)
HCV RNA > 800,000 IU/ml – no (%)	16 (64)	14 (56)	7 (70)
Median creatinine mg/dL (IQR)	0.83 (0.74, 0.91)	0.81 (0.72, 0.94)	0.74 (0.64, 0.95)

Continuous variables are shown as median (IQR), Categorical variables are expressed as frequencies (%), +Race was self-reported. Body mass index is the weight in kilograms divided by the height in meters squared. Baseline characteristics were similar between groups except higher baseline HCV RNA in part 1 (p=0.03) Weight based RBV: 1000-1200mg/day, Low dose RBV: 600mg/day.

VIROLOGIC RESPONSE

Twenty-four (96%) participants on each randomized arm achieved viral suppression by week 4. Four participants were taken off study drug by week 8 due to non-adherence (1 on weight-based ribavirin; 3 on low-dose RBV; Figure 1). One patient declined to continue study drug past week 12, but his viral load remained undetectable 24 weeks after stopping treatment and he is included in the final ITT analysis. A total of seven (28%) participants on weight-based ribavirin and ten (40%) of participants on low-dose ribavirin relapsed after treatment completion leading to SVR₂₄ rates of 68% (95% CI: 46%-85%) and 48% (95% CI 28%-69%) respectively (p=0.251). The on-protocol analysis is shown in eTable 3).A within-cohort comparison of baseline factors related to SVR was performed and is shown in eTable 4 (ITT analysis). Deep sequencing of all baseline samples and select samples from relapsers showed no S-282T containing mutations.

–Viral Kinetic, Pharmacokinetic and Pharmacodynamic Modeling

All participants experienced a rapid decline in plasma HCV RNA. A VK model over the first 50 days of treatment of all randomized participants showed no differences in viral decay between the two arms or by baseline characteristics (Figure 2; individual patient slopes: eFigure 1). However, a fully fitted PK-VK model of a subset of 20 randomized participants showed a significantly slower loss rate of free virus(c) in relapsers compared to participants who achieved SVR (c: 3.57 vs. 5.60/day p = 0.009). There were no observable differences in viral decay, drug efficiency, loss rate of infected cells, or loss rate of infectious virus based on baseline characteristics (eTable 5).

Figure 2. Viral kinetic (VK), pharmacokinetic (PK) and pharmacodynamics (PD) curves.

Fitted curves for hepatitis C viral kinetics (VK) in 50 randomized participants (a and b), pharmacokinetics and pharmacodynamics (PK-PD) in 20 randomized participants (c), and pharmacodynamics and viral kinetic (PD-VK) in 20 randomized participants (d). Median fitted curves are plotted for viral decay (VK) (a); median viral decay curves were rapid and independent of ribavirin dosing(b); median efficiency of drug blocking viral production (PK-PD model) was similar in SVR vs. relapsers (c) PK-VK model for viral decay in SVR vs. relapsers (d) SVR: Sustained virologic responders; Weight-based ribavirin: 1000-1200mg/day, Low-dose ribavirin: 600mg/day.

HISTOLOGIC RESPONSE

Twenty-nine (58%) participants had paired liver biopsies with an improvement in inflammation in 27 (93%) participants with a median drop of 5 points (15 point scale) (eFigure 2). In parallel with HCV RNA decline, there was rapid improvement of alanine aminotransferase (ALT) levels with 77% and 98% of participants normalizing by day 7 and 14, respectively. A similar pattern was observed with aspartate aminotransferase (AST) levels. (eFigure 2)

SAFETY

The combination of sofosbuvir and ribavirin was safe and well tolerated with no death or discontinuation of treatment due to adverse events. The most frequent adverse events were headache, anemia, fatigue and nausea, which were mild to moderate (Table 2). There were seven grade 3 events in the entire study. In participants receiving weight-based ribavirin, there was a higher incidence of hemoglobin decline, which was maintained through week 12 compared to participants receiving low-dose ribavirin (wk. 4: 37% vs. 4% p=0.0046; wk12: 39% vs. 4% p=0.0098) (eFigure 3). Eight participants (five on weight-based ribavirin) underwent ribavirin dose reduction for decreased hemoglobin including three with a history of coronary artery disease with ribavirin reduction instituted at a hemoglobin level of < 12g/dL. There was no use of erythropoietin stimulating agents in this study. No major biopsy related complications were observed.

Table 2. Adverse Events During the Treatment Period.

Adverse event – N (%)	Randomized part
	Sofosbuvir + Weight-based RBV N=25	Sofosbuvir + Low-dose RBV N=25
Death	0	0
Any serious adverse event	0	1 (4)
Any grade 3/4 event	1 (4)	5 (20)
Any discontinuation owing to an adverse event	0	0
Ribavirin dose reduction	5 (20)	3 (12)
Headache	7 (28)	7 (28)
Anemia	8 (32)	4 (16)
Fatigue	4 (16)	6 (24)
Nausea	4 (16)	5 (20)
Dyspnea	2 (8)	2 (8)
Vomiting	1 (4)	3 (12)
Dizziness	2 (8)	1 (4)
Pruritic rash	2 (8)	0
Myalgia	0	2 (8)
Laboratory abnormality
Anemia
Grade 1 (10.0-10.9 g/dL)	6 (24)	3 (12)
Grade 2 (9.0-9.9 g/dL)	2 (8)	0
Grade 3 (7.0-8.9 g/dL)	0	1 (4)
Hyperbilirubinemia
Grade 1 (1.1-1.5 × ULN)	4 (16)	2 (8)
Grade 2 (1.6-2.5 × ULN)	3 (12)	1 (4)
Hypophosphatemia
Grade 2 (2.0-2.4 mg/dL)	6 (24)	6 (24)
Grade 3 (1.0-1.9 mg/dL)	0	2 (8)
Neutropenia
Grade 3 (500-749/mm3)	0	1 (4)
Hypocalcemia (<2.04 mmol/L)	6 (24)	5 (20)
Hypomagnesemia (<0.63 mml/L)	0	1 (4)
Elevated serum creatinine (>1.1× ULN)	1 (4)	3 (12)

All adverse events that occurred during the study in at least 2 subjects in any group are included regardless of relatedness to study drug. The grade 3 events were neutropenia in a patient with a baseline absolute neutrophil count of 850 (1), anemia with a hemoglobin < 9g/dL in a patient who underwent abdominoplasty (1), nausea which resolved within 48 hours (1) and hypophosphatemia <1.9mg/dL(2). There was one serious adverse event in a morbidly obese patient who developed cholelithiasis with elevated lipase and transient pancreatitis 3 weeks after completion of study drug. This issue was resolved with elective cholecystectomy and was not considered related to study drug. Weight based RBV: 1000-1200mg/day, Low dose RBV: 600mg/day.

PREDICTORS OF RELAPSE

Bivariable analysis of baseline factors showed that in all randomized participants who completed treatment, the odds of relapse was significantly higher in participants who were male (OR: 6.09; 95% CI 1.17-31.6), had advanced fibrosis (OR: 4.27 95% CI: 1.1-16.54) and baseline HCV RNA > 800,000 IU/mL (OR:5.74, 95% CI: 1.35-24.38) (Table 3). Given the small number of events, the exploratory nature of the stepwise analysis that determined variables used in the model and the instability of multivariable logistic regression, only the bivariable model results are reported in the paper.

Table 3. Bivariable model of treatment relapse based on baseline characteristics.

Baseline characteristic	Odds Ratio Estimate	95% Confidence Intervals	p-value
RBV Dose: Low dose vs weight-based	2.024	(0.600,6.828)	0.2559
Age: >50yrs vs. ≤ 50yrs	1.777	(0.401,7.880)	0.4491
Genotype: 1a vs. 1b	0.478	(0.125,1.827)	0.2808
Race: Black vs. non black	1.957	(0.348,11.008)	0.4464
Gender: Male vs. Female	6.091	(1.174,31.614)	0.0315
IL28B Genotype: CT/TT vs. CC	1.200	(0.196,7.362)	0.8438
BMI: >30 vs. ≤ 30	0.333	(0.096,1.159)	0.0839
Knodell HAI fibrosis: 3-4 vs. 0-1	4.267	(1.101,16.537)	0.0358
HCV RNA: >800, 000vs. ≤800, 000	5.743	(1.353,24.381)	0.0178

Bivariable analysis of baseline factors showed that in all randomized participants who completed treatment, the odds of relapse was significantly higher in participants who were male, had advanced fibrosis and baseline HCV RNA > 800,000 IU/mL. RBV: ribavirin; BMI: Body mass index;

DISCUSSION

Although the treatment of HCV is rapidly evolving several questions remain unanswered. To our knowledge this study is the first to show the efficacy of a promising, interferon-free regimen in a traditionally difficult to treat population while exploring the reasons for treatment relapse. In the present study, treatment of chronic HCV infection with a single DAA (sofosbuvir) and weight-based ribavirin resulted in a higher SVR rate in an inner city population with a high prevalence of unfavorable traditional treatment predictors than reported rates with currently utilized interferon-based therapy in similar populations. ^7,8 In comparison to the registration trials with boceprevir and telaprevir, this population had a higher prevalence of unfavorable traditional predictors such as black race (80% vs. 7-15%); genotype 1a (70% vs.60-64%); advanced fibrosis (24% vs. 9 -20%) and BMI ≥ 30 (49% vs. 22%). ^7,8 The overall SVR rate in participants that received sofosbuvir in combination with weight-based ribavirin in this study was slightly lower (68%) than the recently reported 84% in a New Zealand study of sofosbuvir and weight-based ribavirin in a predominantly Caucasian, treatment naive population.¹¹. As treatment of HCV is evolving from an IFN-based combination therapy to an all oral, IFN-free DAA regimen, these results are somewhat encouraging and provide important information regarding the expected treatment responses using interferon-free DAA therapies in a population representative of the U.S epidemic.

We investigated host and viral factors and found that three baseline factors namely male gender, advanced liver disease and high baseline HCV RNA were associated with relapse in a bivariable model. Similar to reported literature on DAA/IFN based regimens ^6-8, advanced fibrosis was associated with higher odds of relapse. In this regard, seven (54%) of the 13 participants with advanced liver fibrosis treated in this study relapsed including all four participants with cirrhosis. Future studies are warranted to evaluate the efficacy of sofosbuvir and ribavirin regimens in participants with advanced fibrosis.

There were no cases of viral breakthrough while receiving therapy in participants treated with sofosbuvir and ribavirin similar to what was reported in prior studies. ¹¹ Comprehensive analysis of plasma HCV quasispecies by 454 deep sequencing failed to detect the characteristic S282T mutants previously associated with resistance to sofosbuvir suggesting that relapse may not be associated with the emergence of this mutant.

The kinetics of HCV decline during interferon and ribavirin therapy has been previously described as a predictor of SVR.^20,21 Since interferon-free DAA therapy is entirely based on achieving maximum suppression of HCV replication, we sought to explore the effect of early HCV VK, PK and PD on therapeutic response. While there were no significant differences in VK or PK between the weight-based ribavirin and low-dose ribavirin arms, the VK-PD model demonstrated a significantly slower loss rate of infectious virus in participants who relapsed. The mechanism of viral relapse in these participants remains elusive and future research will be focused on identifying the biological basis for incomplete clearance of HCV in these participants. Limitations of this study include the relatively small sample size in each arm and a higher though small increase in the number of discontinuations in the low dose ribavirin arm.

Given that ribavirin is associated with significant adverse events ^13,23 but appears to be essential for optimal response to interferon-based and certain DAA therapies, ^11,14,15it is important to determine the optimal dose of ribavirin in the treatment of chronic HCV infection. In this regard, our study showed a trend towards an increased SVR rate in patients receiving weight-based ribavirin suggesting that weight-based ribavirin might be necessary to achieve optimal responses with sofosbuvir when used in a single DAA regimen.

In conclusion, a combination of sofosbuvir and weight-based ribavirin appears to be an effective regimen to treat chronic HCV infected patients with poor prognostic factors that are representative of the demographics of the U.S HCV epidemic. Furthermore the delineation of the host and viral factors predictive of treatment relapse with different DAA regimens is needed. As newer DAA regimens with promising results are being evaluated, it is important that these studies involve populations most affected by hepatitis C.