Primary biliary cholangitis (PBC) is a chronic autoimmune liver disease characterised by destruction of the intrahepatic bile ducts leading to liver inflammation and fibrosis, and ultimately liver cirrhosis and end-stage liver disease. More than 50% of patients with PBC suffer from chronic fatigue, and approximately 20% suffer from severe fatigue with negative impact on their quality of life. Although fatigue is a large problem in patients with PBC, no effective treatments are available.

A Danish intervention study have shown that high dose oral thiamine (Vitamin B1) were effective in treating chronic fatigue in patients with inflammatory bowel disease. In this study, only few and minor adverse events to thiamine treatment were observed. Although the precise mechanism of work remains unknown, the investigators see no reason that this cannot be transferred topatients with PBC. Hence, the investigators aim to conduct a study investigating the use of oral thiamine in chronic fatigued patients with PBC.

The study will be conducted as a double-blinded, placebo-controlled, randomised, crossover trial including 36 patients with PBC and with a higher fatigue level than in the general population for more than six months. The patients will be randomised into one of two 3x4 weeks setups; 1) thiamine for four weeks followed by four weeks washout and finally four weeks of placebo or 2) placebo for four weeks followed by four weeks washout and finally four weeks of thiamine. The primary endpoint is to investigate the fatigue-level before and after treatment with thiamine and placebo using every patient as their own control. Fatigue-level will be measured using international validated questionnaires. The doses of thiamine are calculated based on the patient gender and weight. All patients will be included in the outpatient clinic at the Department of Hepatology and Gastroenterology at Aarhus University Hospital.

Inclusion Criteria:

• PBC for more than 3 months
• PBC-40 fatigue score >32
• Fatigued for at least 6 months

Exclusion Criteria:

• Comorbidity that can explain fatigue
• Non-compliant patients
• Pregnancy
• Expected surgical interventions during the study period
• Chronic kidney disease (eGFR<60)