Titrating-Dose of Lonafarnib in Combination With Ritonavir

Key Inclusion Criteria: 1. Male or female, 18 to 65 years of age, inclusive 2. Chronic HDV infection documented by a positive HDV antibody (Ab) test of at least 6 months duration and detectable HDV ribonucleic acid (RNA) by quantitative polymerase chain reaction (qPCR) at study entry 3. Liver biopsy demonstrating evidence of chronic hepatitis 4. Willingness to practice appropriate contraception Key Exclusion Criteria: 1. Previous use of lonafarnib 2. Co-infected with human immunodeficiency virus (HIV) or hepatitis C virus (HCV) 3. Active jaundice defined by total bilirubin level \>2.0 mg/dL and known not to have Gilbert's disease 4. Decompensated liver disease or cirrhosis, history of bleeding esophageal varices, ascites, or hepatic encephalopathy 5. Serum creatinine concentration ≥1.5 times upper limit of normal (ULN) 6. Evidence of another form of viral hepatitis (not including hepatitis B virus or HCV) or another form of liver disease 7. Evidence of hepatocellular carcinoma 8. Use of alfa interferon, either interferon alfa-2a or interferon alfa-2b, or peginterferon alfa-2a within 2 months before the start of screening 9. Concomitant use of any of the following: 1. Medications or foods that are known moderate or strong inducers or inhibitors of CYP3A4 or CYP2C19 2. Drugs known to prolong the PR interval or QT interval of the electrocardiogram 3. Receipt of systemic immunosuppressive therapy within the 3 months before start of screening 4. Statins, due to inhibition of mevalonate synthesis, which reduces protein prenylation 5. Medications contraindicated in the prescribing information for ritonavir