Patient description: A 53-year-old man presents with chronic HCV infection for the past 2 years. His past medical history is only significant for inguinal hernia surgery when he was 20 years old. He is on IFN (100 mg/week) plus RBV (400 mg/day) combination therapy for the past 9 months. Direct antiviral drugs were added to his treatment 6 months ago. His medical record shows previous positive HCV RNA tests as well as positive enzyme immunoassay for anti-HCV-antibodies. The recent biopsy was negative for hepatocellular carcinoma and was only remarkable for chronic inflammation compatible with a chronic viral hepatitis. There is no evidence of alcoholic liver disease, bleeding from esophageal varices, hemochromatosis, autoimmune hepatitis or metabolic liver disease. He is an alert male with no acute distress. His BP: 130/75, HR: 90/min and BMI: 27. His abdomen is soft with no ascites or tenderness. The lower extremities are normal with no edema.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Hepatitis c for Part A Subjects must meet all of the following to be eligible for participation in this study. 1. Willing and able to provide written informed consent. 2. Male or female, age ≥ 18 years. 3. HCV RNA ≥ 104 IU/mL at screening. 4. Confirmed chronic HCV infection as documented by either: a. a positive anti-HCV antibody test or positive HCV RNA or positive HCV genotyping test at least 6 months prior to the Baseline/Day 1 visit, or 5. HCV genotype 4 at screening as determined by the Central Laboratory. Any non-definitive results will the subject from study participation. 6. The subject's medical records must be sufficient to categorize prior treatment history as one of the following: i) IFN-intolerant: subject had documented intolerance to IFN during prior IFN therapy of up to 12 weeks duration ii) Non-response: subject did not achieve undetectable HCV RNA levels on treatment iii) Relapse/Breakthrough: subject achieved undetectable HCV RNA levels during treatment or within 4 weeks after treatment and later showed detectable HCV RNA An Absence of cirrhosis is defined as any one of the following Liver biopsy within 2 years of Screening showing absence of cirrhosis Fibroscan with a result of ≤ 12.5 kPa within 6 months of Baseline/Day1 FibroTest score of ≤ 0.48 AND APRI of ≤ 1 performed during Screening In the absence of a definitive diagnosis of the presence or absence of cirrhosis by the above a liver biopsy is required. Liver biopsy results supersede the results obtained by Fibroscan or Fibro Test. 7. Body mass index (BMI) ≥ 18 kg/m2. 8. Screening ECG without clinically significant abnormalities. 9. Subjects must have the following laboratory parameters at screening ALT ≤ 10 x the upper limit of normal (ULN) AST ≤ 10 x ULN Hemoglobin ≥ 12 g/dL for male, ≥ 11 g/dL for female subjects Platelets > 50,000 cells/mm3 INR ≤ 1.5 x ULN unless subject has known hemophilia or is stable on an anticoagulant regimen affecting INR Albumin ≥ 3 g/dL  for Part A Subjects who meet any of the following are not to be enrolled in this study. 1. for treatment naïve subjects only: Prior exposure to IFN, RBV, or other approved or experimental direct-acting antiviral targeting the HCV. 2. for treatment-experienced subjects: prior exposure to a NS5a inhibitor, NS5b nucleotide inhibitor, or NS5b non-nucleotide inhibitor targeting the HCV 3. Pregnant or nursing female or male with pregnant female partner. 4. Chronic liver disease of a non-HCV etiology (eg, hemochromatosis, Wilson's disease, α1 antitrypsin deficiency, cholangitis). 5. Infection with hepatitis B virus (HBV) or human immunodeficiency virus (HIV). 6. Contraindication to RBV therapy e.g., history of clinically significant hemoglobinopathy (sickle cell disease, thalassemia). 7. History of malignancy diagnosed or treated within 5 years (recent localized treatment of squamous or non-invasive basal cell skin cancers is permitted; cervical carcinoma in situ is allowed if appropriately treated prior to screening); subjects under evaluation for malignancy are not eligible. 8. Chronic use of systemically administered immunosuppressive agents (eg, prednisone equivalent > 10 mg/day). 9. Clinically-relevant drug or alcohol abuse within 12 months of screening. A positive drug screen will subjects unless it can be explained by a prescribed medication; the diagnosis and prescription should be approved by the investigator. 10. History of solid organ transplantation. 11. Current or prior history of clinical hepatic decompensation (eg, ascites, variceal hemorrhage, hepatic encephalopathy, hepatorenal syndrome and hepatopulmonary syndrome). 12. History of clinically-significant illness or any other major medical disorder that may interfere with subject treatment, assessment or compliance with the protocol. 13. History of a gastrointestinal disorder (or post-operative condition) that could interfere with the absorption of the study drug. 14. History of significant pulmonary disease, significant cardiac disease or porphyria. 15. Excessive alcohol ingestion, defined as 3 glasses/day (1 glass is equivalent to 284 mL beer, 125 mL wine, or 25 mL distilled spirits) for females and 4 glasses/day for males. 16. History of difficulty with blood collection and/or poor venous access for the purposes of phlebotomy. 17. Donation or loss of more than 400 mL blood within 2 months prior to Baseline/Day 1. 18. Known hypersensitivity to RBV, the study investigational medicinal product, the metabolites, or formulation excipients for Part B Subjects who meet any of the following are not to be enrolled in this study. 1. For treatment naïve subjects only (Cohort 1): Prior exposure to IFN, RBV, or other approved or experimental direct-acting antiviral targeting the HCV. 2. Current or prior history of any of the following: A Clinical hepatic decompensation (ie, ascites, encephalopathy or variceal hemorrhage) B Clinically-significant illness (other than HCV) or any other major medical disorder that may interfere with subject treatment, assessment or compliance with the protocol, or, current evaluation for a potentially clinically significant illness (other than HCV) C Gastrointestinal disorder or post-operative condition that could interfere with the absorption of the study drug D Solid organ transplantation E Significant pulmonary disease, significant cardiac disease or porphyria F Psychiatric hospitalization, suicide attempt, and/or a period of disability as a result of their psychiatric illness within the last 5 years Subjects with psychiatric illness (without the prior mentioned conditions) that is well-controlled on a stable treatment regimen for at least 6 months prior to Baseline/Day 1 or that has not required medication in the last 12 months may be enrolled. G Any malignancy within the 5 years prior to screening, with the exception of specific cancers that are cured by surgical resection (basal cell skin cancer, etc.), or current evaluation for possible malignancy H Difficulty with blood collection and/or poor venous access for the purposes of phlebotomy I Significant drug allergy (such as anaphylaxis or hepatotoxicity) 3. Chronic liver disease of a non-HCV etiology (eg, hemochromatosis, Wilson's disease, α1 antitrypsin deficiency, cholangitis) 4. Infection with hepatitis B virus (HBV) or human immunodeficiency virus (HIV) 5. Use of any prohibited concomitant medications 6. Contraindication to RBV therapy, including significant history of clinically significant hemoglobinopathy (eg, sickle cell disease, thalassemia) 7. In the judgment of the investigatory, any clinically-relevant drug or alcohol abuse within 12 months of screening that may interfere with subject treatment, assessment of compliance with the protocol 8. Pregnant or nursing females or male with pregnant female partner 9. Known hypersensitivity to RBV, SOF, or formulation excipients