Differences Between Peginterferon Alfa 2a and 2b

Interferon is a drug that mimics a protein in the body that the immune system uses to destroy viruses. Pegylated interferon is a modified form of the drug that is able to stay in the body longer, which provides better treatment. Polyethylene glycol (PEG) is added to the interferon, a process called pegylation, which is used with other kinds of drugs as well.

The Hepatitis C virus.
SCIEPRO / Getty Images

Two kinds of pegylated interferons are available and used to treat Hepatitis C virus infection.

  • Peginterferon alfa-2a: Also called alfa-2a, commercial name Pegasys.
  • Peginterferon alfa-2b: Also called alfa-2b, commercial name PegIntron.

They were considered the treatment of choice, used with ribavirin, and listed on the World Health Organization's List of Essential Medicines. The treatment of HCV is changing with the approval of Sofosbuvir (Sovaldi) and Simeprevir (Olysio) in 2013 by the FDA. These newer medications and others sure to follow may displace the peginterferons as the preferred treatment.

The main difference between these two pegylated interferons is in the dosing. Alfa-2a is used as a fixed weekly dose. Alfa-2b is used as a weekly dose based on the weight of the patient. There are other differences between the two drugs, but they are mostly technical and are used by the prescribing physician. For example, alfa-2a has a relatively constant absorption after injection and is distributed mostly in the blood and organs. But alfa-2b has a rapid absorption and a wider distribution in the body.

Differences in Effectiveness

Until January 2008, no data directly compared these two medicines. That has changed with a large clinical study known as IDEAL and further clinical comparisons. These provide interesting results that will allow physicians additional insight into these powerful chronic hepatitis C therapies.

The IDEAL study — Individualized Dosing Efficacy versus Flat Dosing to Assess Optimal Pegylated Interferon Therapy — involved 3070 individuals in a randomized controlled trial. It found similar effectiveness between alfa-2a and alfa-2b in sustained virological response rate. Alfa-2a had a rate of 41% and alfa-2b had an SVR of 39%.

But the case was not closed. Two more studies found statistically significant differences between the two drugs, with alfa-2a the clear winner by over 12% better rates in SVR.

A further meta-analysis of 3,518 patients from seven randomized controlled trials found better results with alfa-2a, although it produced a higher rate of neutropenia. Neutropenia is a reduction in the number of white blood cells. This is a side effect that is not desirable, as white blood cells are the major component of the body's immune system. When they are reduced, you would be more vulnerable to infection and less able to fight off bacteria and viruses.

These results will likely be taken into consideration when recommending treatment. But newer therapies have displaced peginterferons as the treatment of choice for chronic hepatitis C. Such is the nature of research and development. It may eventually be moot to compare these two drugs as newer treatments will be preferred.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  • Hepatitis C FAQs for Health Professionals, October 14, 2015. Centers for Disease Control and Prevention.

  • Alavian SM, Behnava B, Tabatabaei SV. The comparative efficacy and safety of peginterferon alpha-2a vs 2b for the treatment of chronic HCV infection: a meta-analysis. Hepat Mon. 2010;10(2):121–31.
  • Ascione A, De Luca M, Tartaglione MT, Lampasi F, Di Costanzo GG, Lanza AG, Picciotto FP, Marino-Marsilia G, Fontanella L, Leandro G. Peginterferon alfa-2a plus ribavirin is more effective than peginterferon alfa-2b plus ribavirin for treating chronic hepatitis C virus infection. Gastroenterology. 2010;138(1):116–22.
  • Berenguer M, Wright TL. Hepatitis C. In: M Feldman, LS Friedman, LJ Brandt (eds), Gastrointestinal and Liver Disease, 8e. Philadelphia, Elsevier, 2006. 1701.
  • McHutchison JG, Lawitz EJ, Shiffman ML, Muir AJ, Galler GW, McCone J, Nyberg LM, Lee WM, Ghalib RH, Schiff ER, Galati JS, Bacon BR, Davis MN, Mukhopadhyay P, Koury K, Noviello S, Pedicone LD, Brass CA, Albrecht JK, Sulkowski MS, IDEAL Study Team. Peginterferon alfa-2b or alfa-2a with ribavirin for treatment of hepatitis C infection. N Engl J Med. 2009;361(6):580–93.
  • Rumi MG, Aghemo A, Prati GM, D'Ambrosio R, Donato MF, Soffredini R, Del Ninno E, Russo A, Colombo M. Randomized study of peginterferon-alpha2a plus ribavirin vs peginterferon-alpha2b plus ribavirin in chronic hepatitis C. Gastroenterology. 2010;138(1):108–15.

By Charles Daniel
 Charles Daniel, MPH, CHES is an infectious disease epidemiologist, specializing in hepatitis.