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What Is a "Pegylated" Drug?


Updated June 10, 2014

What Is a

Pegasys is an example of a pegylated interferon for treating chronic hepatitis.

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Question: What Is a "Pegylated" Drug?
Answer: Pegylated interferon is one of the powerful drugs that treat chronic hepatitis. What does the "pegylated" mean and why is it important? If you take a weekly injection of interferon, you owe thanks to a chemist. This is because without the chemistry of pegylation you would need to inject interferon up to three times a week. In short, pegylation makes taking your medicine easier and actually makes it work better.

Pegylated interferon, usually called peginterferon, is a chemically modified form of the standard interferon that treats hepatitis C and rarely hepatitis B. The difference between interferon and peginterferon is the PEG, which stands for a molecule called polyethylene glycol. The PEG does nothing to fight the virus. But by attaching it to the interferon (which does fight the virus), the interferon will stay in the body (specifically the blood) much longer.

This benefits you by only needing one weekly infection and by giving you a higher rate of sustained virologic response. Many drugs can be pegylated. In addition to interferon (such as Pegasys and PegIntron), several pegylated drugs are used to treat various cancers and their side effects.


Katzung, BG. Basic and Clinical Pharmacology, 10e. New York, McGraw-Hill, 2007.

Brenner GM, Stevens, CW. Pharmacology, 2e. Philadelphia, Saunders Elsevier, 2006.

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