Raw research findings for this medication. Mostly single studies, not curated or confirmed robust.
Peginterferon alfa-2a is interferon alfa-2a attached to a large polyethylene glycol (PEG) molecule so it lasts a week. It boosts the body's antiviral and immune defences. It is used for chronic hepatitis B, was used with ribavirin for chronic hepatitis C, and is used off label for some blood disorders such as polycythaemia vera. It is sold as Pegasys.
Response of hepatitis C to peginterferon and ribavirin depended strongly on the IFNL3 (IL28B) region: people with the CC genotype at rs12979860 cleared the virus far more often. CPIC published a guideline on IFNL3 for this treatment. In hepatitis B, the same region has been studied with smaller effects. Interferon-free hepatitis C medicines have since made the gene much less important.
Every published finding on gene variants and Pegasys. Upload your DNA file to see which of these rows apply to you.
PharmGKB weighs all studies of a variant and rates how strong the evidence is, from 1A (strongest) to 4.
IFNL3;IFNL4 rs12979860: Level 1A · replicated. Efficacy: Hepatitis C virus infection. 69.
IFNL3;IFNL4 rs12979860: Level 1A · replicated. Efficacy: Chronic hepatitis C virus infection. 9.
IFNL3;IFNL4 rs12979860: Level 1A · replicated. Efficacy: Chronic hepatitis C virus infection. 5.
IFNL3 rs8099917: Level 1B · replicated. Efficacy: Chronic hepatitis C virus infection. 45.
Studies of how well it worked in people carrying a variant.
Studies of how much of the drug people needed or tolerated.
Study findings and evidence levels: PharmGKB (CC BY-SA 4.0). Guidelines: CPIC and DPWG, as bundled in PharmCAT. Most studies were done mainly in people of European ancestry.
More drugs from the same category
Interferon alfa-2a (Interferons)
Not a prescribing recommendation. This page is educational information about pharmacogenomic research and clinical guidelines - it is not medical or dosing advice, and not a prediction of how any medication will work for you. Never start, stop, or change a medication or dose based on it; talk to your doctor or pharmacist, who can order clinical-grade testing if appropriate.
Content updated September 2026.
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