To examine the safety, tolerability, and efficacy of daily dosing with vidofludimus calcium over a 6-month period.

Investigators will assess the following:

1. Changes on serum alkaline phosphatase levels at 3 & 6 months.
2. Changes in other liver biochemistries at 3 & 6 months.
3. Changes in IL-17 &IFNγ levels at 6 weeks and 6 months.

Inclusion Criteria:

1. Male or female subject age 18-75 years
2. Diagnosis of PSC consistent with the guidelines published by the AASLD. All subjects must have an elevated serum ALP of at least 1.5 times upper limit of normal (ULN) at baseline plus cholangiographic evidence of PSC (MRI, endoscopic retrograde cholangiography, or direct cholangiography).
3. Indirect bilirubin <1.2 times the ULN
4. An ultrasound (or equivalent imaging modality) that excludes biliary obstruction and malignancy within 6 months of study enrollment
5. PSC with or without inflammatory bowel disease, such as ulcerative colitis or Crohn's disease
6. Must agree to comply with the study protocol and provide informed consent

Exclusion Criteria:

1. Pregnancy, attempting to become pregnant, or breastfeeding
2. Active hepatitis A or B infection
3. Active hepatitis C infection (antibody positive); patients with a history of hepatitis C infection will be eligible for this study if they have undetectable levels of HCV RNA
4. HIV/AIDS (per medical record or HIVAb/HIA antigen), tuberculosis, or positive interferon-gamma assay (IGRAs) for Mycobacterium tuberculosis
5. Other cholestatic liver disease such as primary biliary cholangitis and cholestatic diseases of pregnancy
6. Metabolic liver diseases such as Wilson's disease, Gilbert's syndrome or hemochromatosis
7. Serum uric acid levels at screening >1.2 ULN
8. Inherited diseases of the liver such as α-1 antitrypsin deficiency
9. Immunoglobulin G4-related cholangitis
10. PSC with concomitant autoimmune hepatitis (AIH) and/or primary biliary cholangitis
11. Secondary sclerosing cholangitis (SSC)
12. Active acute ascending cholangitis requiring antibiotics
13. CCA (malignant biliary stricture, neoplasm, and cytology/histopathology or positive fluorescence in situ hybridization (FISH) consistent with adenocarcinoma of the bile duct)
14. A liver biopsy, if one has been previously obtained, which showed non-alcoholic steatohepatitis (NASH). Patients with suspected fatty liver by imaging will not be excluded.
15. Presence of complications of advanced PSC such as hepatic encephalopathy, portal hypertension, hepato-renal syndrome, and hepato-pulmonary syndrome
16. History of liver transplantation, anticipated need for liver transplantation within 12 months from randomization, a Model of End-stage Liver Disease (MELD) score of ≥15, or a Child Pugh score >6
17. Ongoing alcohol abuse (>4 drinks per day for men, and >2 drinks per day for women)
18. Moderate-to-severe renal impairment with a calculated creatinine clearance of <60mL/min
19. Any other conditions or abnormalities that, in the opinion of the investigator, may compromise the safety of the subject or interfere with the subject participating in or completing the study
20. Evidence of, or treatment for, C. difficile infection within 30 days before the initiation of the study drug
21. Evidence of active C. difficile infection during the screening phase confirmed by a positive C. difficile toxin B
22. Subjects who have been treated for intestinal pathogens other than C. difficile infection within 30 days prior to study drug initiation
23. Received or plan to receive live vaccine within 30 days prior to, and through the end of the study
24. Use of methotrexate at dose ≥17.5mg/week
25. Rosuvastatin exceeding 10 mg daily

Adverse Events were collected from baseline to end of study, approximately 8 months