Rebif^® (interferon beta-1a) is a purified 166 amino acid glycoprotein with a molecular weight of approximately 22,500 daltons. It is produced by recombinant DNA technology using genetically engineered Chinese Hamster Ovary cells into which the human interferon beta gene has been introduced. The amino acid sequence of Rebif^® is identical to that of natural fibroblast derived human interferon beta. Natural interferon beta and interferon beta-1a (Rebif^®) are glycosylated with each containing a single N-linked complex carbohydrate moiety.

Using a reference standard calibrated against the World Health Organization natural interferon beta standard (Second International Standard for Interferon, Human Fibroblast GB 23 902 531), Rebif^® has a specific activity of approximately 270 million international units (MIU) of antiviral activity per mg of interferon beta-1a determined specifically by an in vitro cytopathic effect bioassay using WISH cells and Vesicular Stomatitis virus. Rebif^® 8.8 mcg, 22 mcg and 44 mcg contan approximately 2.4 MIU, 6 MIU or 12 MIU, respectively, of antiviral activity using this method.

Rebif^® (interferon beta-1a) is formulated as a sterile solution in a prefilled syringe intended for subcutaneous (sc) injection. Each 0.5 ml (0.5 cc) of Rebif^® contains either 22 mcg or 44 mcg of interferon beta-1a, 2 or 4 mg albumin (human) USP, 27.3 mg mannitol USP, 0.4 mg sodium acetate, Water for Injection USP.

Each 0.2 mL (0.2 cc) of Rebif^® contains 8.8 mcg of interferon beta-1a, 0.8 mg albumin (human) USP, 10.9 mg mannitol USP, 0.16 mg sodium acetate, and Water for Injection USP.

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