Pegasys

Pegasys is the brand name for pegylated interferon alfa-2a, a long-acting form of recombinant human interferon used in antiviral and anticancer therapy. The interferon alfa-2a molecule is covalently attached to polyethylene glycol (PEG), which increases its circulating half-life and allows once-weekly subcutaneous injections.

Mechanism of action is through binding to interferon receptors on cell surfaces, activating the JAK-STAT signaling pathway. This leads to increased expression of antiviral proteins and modulation of the immune response, contributing to antiviral effects and antiproliferative activity.

Indications and uses have traditionally included chronic hepatitis C in adults (typically in combination with ribavirin) and chronic hepatitis B in adults with compensated liver disease. Pegasys has also been used in other conditions such as certain hematologic malignancies and Kaposi’s sarcoma, though its use for these indications has declined with the advent of newer therapies.

Administration and dosing are by subcutaneous injection once weekly. Dosing is generally weight-based for hepatitis C, with treatment durations ranging from several months depending on genotype and response. In hepatitis B, courses may extend over many months and require regular monitoring. Dose adjustments may be necessary for adverse events or laboratory abnormalities.

Common adverse effects include flu-like symptoms, fatigue, cytopenias (such as anemia and neutropenia), mood changes including depression, thyroid dysfunction, autoimmune phenomena, and injection-site reactions. Because of potential serious side effects, patients require regular monitoring of blood counts, liver enzymes, thyroid function, and mental health.

Over time, pegylated interferon therapy for hepatitis C has largely been supplanted by direct-acting antivirals, though Pegasys remains part of the therapeutic landscape for selected conditions and patients.