Pegylated interferon (PEG-IFN) is a class of medication that includes three different drugs as of 2012: Pegylated interferon-alpha-2a Pegylated interferon-alpha-2b Pegylated interferon-beta-1a In these formulations, Polyethylene glycol (PEG) is added to make interferon last longer in the body. They are used to treat both hepatitis B, hepatitis C and multiple sclerosis. Pegylated interferon is contraindicated in patients with hyperbilirubinaemia. References Antiviral drugs Immunostimulants World Health Organization essential medicines