pegylated interferon pegylated interferon 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.