Patients

We enrolled patients at 81 sites in the United States, Canada, Europe, and Hong Kong from July 18, 2014, through December 19, 2014. Eligible patients were 18 years of age or older who had chronic infection with HCV genotype 1, 2, 4, 5, or 6. All patients provided written informed consent.

The original clinical-development program for sofosbuvir–velpatasvir involved two trials — one in patients with HCV genotype 1, 2, 4, 5, or 6 (ASTRAL-1) and one in patients with HCV genotype 3. A separate trial with an active comparator group was deemed to be necessary for patients with HCV genotype 3 in light of the special clinical challenges presented in this population. After the protocol for the present study was finalized and trial activity had begun, the Food and Drug Administration requested a separate trial with an active comparator for patients with HCV genotype 2. Because enrollment in the present study had already begun, we did not amend the protocol to exclude patients with HCV genotype 2. Therefore, two additional phase 3 trials were conducted to evaluate sofosbuvir–velpatasvir in patients with HCV genotype 2 (ASTRAL-2) and HCV genotype 3 (ASTRAL-3), and the results are reported now in the Journal.14,15

The protocol targeted an enrollment of approximately 20% of patients who had been previously treated for HCV with a regimen containing interferon and who had not had a sustained virologic response. Those who had discontinued previous HCV treatment because of an adverse event were not eligible. Patients who had previously received any nucleotide analogue HCV NS5B inhibitor or any NS5A inhibitor were not eligible. Approximately 20% of patients could have evidence of cirrhosis, which was defined as liver-biopsy results showing a Metavir fibrosis score of 4 or an Ishak score of 5 or more, a FibroTest score of more than 0.75 and a ratio of aspartate aminotransferase to platelets of more than 2, or a FibroScan reading of more than 12.5 kPa. There were no upper limits for age or body-mass index. Patients with a history of hepatic decompensation or hepatocellular carcinoma were not eligible for enrollment. Full eligibility criteria are provided in the protocol, available with the full text of this article at NEJM.org.

Study Design

In this multicenter, double-blind, placebo-controlled trial, patients with HCV genotype 1, 2, 4, or 6 were randomly assigned in a 5:1 ratio to receive a fixed-dose combination tablet containing 400 mg of sofosbuvir and 100 mg of velpatasvir, administered orally once daily for 12 weeks, or a placebo tablet to match the active treatment once daily for 12 weeks. Patients in the placebo group were eligible for deferred treatment with 12 weeks of sofosbuvir–velpatasvir. Randomization was stratified according to genotype (1, 2, 4, 6, or indeterminate) and the presence or absence of cirrhosis. Given the low prevalence of genotype 5 HCV infection in the regions in which the study was conducted, we targeted the enrollment of only 20 patients with HCV genotype 5. These patients did not undergo randomization but were enrolled in the sofosbuvir–velpatasvir group only.

Study Assessments

Serum HCV RNA was measured by means of the COBAS AmpliPrep/COBAS TaqMan HCV Quantitative Test, version 2.0 (Roche Molecular Systems), with a lower limit of quantification of 15 IU per milliliter. HCV genotype and subtype were determined with the use of the VERSANT HCV Genotype INNO-LiPA 2.0 assay (Siemens). IL28B genotyping was performed by means of polymerase-chain-reaction amplification and sequencing of the rs12979860 single-nucleotide polymorphism.

Assessments during treatment included standard laboratory testing, serum HCV RNA, vital signs, electrocardiography, and symptom-directed physical examinations. All adverse events were recorded and graded according to a standardized scale. (Details are provided in the study protocol.)

Deep sequencing of the target regions of velpatasvir and sofosbuvir, HCV NS5A and NS5B, respectively, was performed for all patients at baseline and again for all patients with virologic failure in samples obtained at the time of failure. The sequences from baseline samples were compared with those obtained at the time of virologic failure to detect emergent resistance-associated variants. Resistance-associated variants that were present in more than 1% of sequence reads are reported.

End Points

The primary efficacy end point was the rate of sustained virologic response, which was defined as an HCV RNA level of less than 15 IU per milliliter at 12 weeks after the end of treatment in all patients who received at least one dose of sofosbuvir–velpatasvir or placebo. Secondary end points included the rate of adverse events and treatment discontinuations because of adverse events.

Study Oversight

This study was approved by the institutional review board or independent ethics committee at each participating study site and was conducted in compliance with the Declaration of Helsinki, Good Clinical Practice guidelines, and local regulatory requirements. The study was designed and conducted by the sponsor (Gilead Sciences) in collaboration with the principal investigators. The sponsor collected the data, monitored study conduct, and performed the statistical analyses. An independent data and safety monitoring committee reviewed the progress and oversight of the study. The investigators, participating institutions, and sponsor agreed to maintain confidentiality of the data. All the authors had access to the data and assume responsibility for the integrity and completeness of the reported data and fidelity to the protocol. The initial draft of the manuscript was prepared by a professional writer employed by Gilead Sciences and the first and last authors with input from all the authors.

Statistical Analysis

The primary efficacy analysis was designed to test for the superiority of the rate of sustained virologic response among patients receiving sofosbuvir–velpatasvir to a prespecified performance goal of 85% by means of a two-sided exact one-sample binomial test. This 85% rate was not a historical control derived from rates of sustained virologic response in prior HCV treatment trials, since it would not be possible to calculate a single historical rate for the different standard treatments recommended for the various genotypes included in this study. Rather, it is a benchmark rate that is based on the general trend toward increasing rates of sustained virologic response in recent years and the general appeal of using a fixed, clinically relevant threshold as a measure of treatment benefit.16 We determined that the enrollment of 500 patients in the sofosbuvir–velpatasvir group would provide a power of 90% to detect an improvement of at least 5 percentage points in the rate of sustained virologic response over the performance goal of 85%, on the basis of the two-sided exact one-sample binomial test at the 0.05 significance level. We used the Clopper–Pearson method to calculate point estimates and two-sided 95% exact confidence intervals for rates of sustained virologic response for the sofosbuvir–velpatasvir group as a whole, as well as according to HCV genotype (1a, 1b, 2, 4, 5, or 6), and various subgroups.

The inclusion of a placebo group was designed to provide the basis for evaluating the safety profile of sofosbuvir–velpatasvir in a population with expected coexisting medical conditions. We used a double-blind approach in the study-group assignments to ensure the elimination of bias in assessments of safety. No formal comparison of safety between the groups was planned.