The cytokines: The interferon family - Pharmaceutical Biotechnology: Concepts and Aapplications - page 229

2b
is then undertaken as a fi nal purifi cation step. The crystalline product is redissolved in phosphate
buffer, containing glycine and human albumin as excipients. After aseptic fi lling, the product is
normally freeze-dried. Intron A is usually sold at fi ve commercial strengths (3, 5, 10, 25, and 50
million IU/vial).
More recently, a number of modifi ed recombinant interferon products have also gained market-
ing approval. These include PEGylated interferons (PEG IntronA and Viraferon Peg (Table 8.8
and Box 8.2) and the synthetic interferon product Infergen. PEGylated interferons are generated
by reacting purifi ed IFN-

a large cold-room adapted to function under cleanroom conditions. Crystallization of the IFN- α

s with a chemically activated form of PEG. Activated methoxypoly-
ethylene glycol is often used, which forms covalent linkages with free amino groups on the inter-
feron molecule. Molecular mass analysis of PEGylated interferons (e.g. by mass spectroscopy, gel

α

Box 8.2

Product case study: ViraferonPeg

ViraferonPeg (tradename) is a PEGylated form of interferon alfa-2b (IFNα-2b) approved for
medical use in the EU since 2000. It differs from native human IFN -2b only by the presence

of covalently attached PEG. ViraferonPeg is indicated for the treatment of chronic hepatitis C
in adults, and is usually administered in combination with the antiviral drug ribavirin. It is pro-
duced via recombinant DNA technology in an engineered E. coli cell line carrying the human
IFN

α

-2b gene. After cell fermentation the interferon is purifi ed from the bacterial culture via
crystallization and multiple chromatographic steps. As part of the downstream processing, the
interferon is incubated with chemically activated PEG (methoxypolyethylene glycol, mPEG),
which spontaneously forms a covalent linkage via selected protein amino acid groups. The
majority of interferon molecules are monoPEGylated with minor quantities of unPEGylated
and diPEGylated product also being produced.
The product is presented in lyophilized format and contains sodium phosphate, sucrose and
polysorbate as excipients. It is usually administered as once-weekly s.c. injections, typically for
periods of 6 months.
Pharmacokinetic studies indicate a plasma half-life of 13-25 h (compared with 4 h for the
unPEGylated molecule) with maximum serum concentrations attained within 15-44 h. The
main clinical study to establish initial safety and effi cacy was a multicentre double blind,
randomized trial involving 1200 patients split into four groups (three treated with increas-
ing concentrations of ViraferonPeg and the fourth being treated with unPEGylated IFNα-
2b (tradename Intron A). The primary effi cacy measure was a composite of viral response,
assessed in terms of reduction in serum viral particle load and normalized liver enzyme
function, and the PEGylated product proved most effective. A subsequent trial showed that a
combination of ribavirin and ViraferonPeg to be more effective than a combination of ribavi-
rin and unPEGylated product.
Common side effects noted include injection site reactions, weakness, dizziness, weight loss
and fl u-like symptoms, with depression being the most common reason for treatment discon-
tinuation. ViraferonPeg is manufactured and marketed by Schering Plough.

α