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3.1.2 Pegylated Interferon

Pegylated interferons give better results than interferon alone, with no apparent difference in side effects.

Polyethylene glycol (PEG) is a substance (anti-freeze) with a high "molecular weight" that is easily excreted in the urine, due to being soluble in water. "PEG" can be linear or branched. It can be attached to interferon alpha, by different types of protein linkages. The larger or branched PEGs lead to a longer, sustained absorption period. PEG attachment to interferon alpha leads to a longer half-life (the amount of time for an original amount to be metabolized by half) of the interferon. In other words, it makes the interferon stay in the body for a longer period of time. This occurs due to decreased "clearance" by the kidney and slower breakdown of protein. In addition, PEG makes it less probable that the immune system would make antibodies against interferon.

Comparisons of the two available pegylated interferons, Peg-Intron and Pegasys have tentatively been made. The two substances differ basically in the size of the molecule involved, (40 kilodalton for Pegasys, 12 "kilodalton" for Peg-Intron) and in the half-life of each product. Peg Intron is distributed widely throughout the body, and Pegasys is distributed to the blood and organs, including the liver. There might be some compartments within the body that Pegasys does not penetrate. Pegasys has a half-life of 50-80 hours, where Peg Intron has a half-life of 30-50 hours, according to San Francisco specialist Dr. Teresa Wright. Roche's Pegasys shows a sustained response rate of 39% compared to 25% for Schering's Peg Intron. Ronald Baker, PhD and Harvey S. Bartnof, MD ( www.hivandhepatitis.com ) warn that a direct comparison of results is difficult, however. The mean baseline viral load levels in the Peg Intron study were not presented, so it’s difficult to compare, and the Peg Intron trial included more genotype 1 patients.



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