A 15-year-old male with a 3-year history of ulcerative colitis has persistently elevated serum alkaline phosphatase and gamma-glutamyl transferase. Magnetic resonance cholangiopancreatography (MRCP) reveals multifocal stricturing and beading of the intra- and extrahepatic bile ducts. A liver biopsy shows features of both bile duct injury and interface hepatitis. In addition to therapy for his inflammatory bowel disease, which therapeutic regimen is specifically indicated for his liver condition?