Avonex (Interferon beta-1a)

Avonex (Interferon beta-1a) is a genetically modified beta interferon produced in mammalian cells.  Along with Rebif (Interferon beta-1a), Avonex (approved 1996 U.S FDA) is one of two Interferon beta-1a formulations approved for treating relapsing forms of MS.  Avonex involves a once-weekly Intramuscular injection, while Rebif involves a subcutaneous injection three times a week.  A 64 week study involving some 700 RRMS patients, Comparative tolerance of IFN beta-1a regimens in patients with relapsing MS, found that overall adverse events were more common with Rebif, and were due predominantly to differences in injection-site reactions.  However, flu-like symptoms were more common with Avonex, and were more severe and persisted for longer.  Overall, the study found that, “Based on superior clinical and magnetic resonance imaging outcomes over an average of 64 weeks, coupled with modest safety differences, the risk-benefit ratio for IFN therapy in RRMS favours the 44 mcg tiw (Rebif) regimen over this period of time.”

Interferons are proteins which are created naturally by the body to defend against viruses.  Avonex and Rebif are made up of exactly the same amino acids (major components of proteins) that are created by the body.  The interferons are effective against MS because they help regulate the immune system to decrease attacks on myelin.  Avonex (Interferon beta-1a) and the other interferon medications, Rebif (Interferon beta-1a) and Betaseron etc.  (Interferon beta-1b), along with Copaxone (Glatiramer acetate), a synthetic protein that simulates myelin basic protein, make up the so-called “CRAB” therapies for MS.  The CRAB medications are the only clinically proven treatments for affecting the underlying course of Multiple Sclerosis, and for decreasing overall exacerbation rate. 

Avonex is given once a week as an intramuscular injection.  Several studies have shown that the 30 microg. dosage produces equivalent results to the 60 microg. dose, and produces fewer side effects.  Avonex can affect liver function and may cause side effects including flu-like symptoms (fatigue, chills, fever, muscle aches, and sweating) and injection site reactions (swelling, redness, discoloration, and pain).  NSAIDs like Naproxen and ibuprofen may be somewhat helpful in minimizing fatigue or muscle and joint pain. 

As interferons are engineered proteins, after several years the body may begin to perceive them as foreign and mount an immune attack by producing "neutralizing antibodies".  The production of these antibodies renders the medications less effective over time.  Studies have shown that antibody production varies between the different interferon medications, after 18 months, ranging from about 31% for Betaseron, 19% for Rebif, and 4% for Avonex.  Many physicians now recommend testing twice a year for the presence of neutralizing antibodies, and switching to another medication if high levels are present.  There is some evidence that switching from a drug that is less capable of producing antibodies, for example switching from Betaseron to Avonex, may be easier and more effective than switching from a less antigenic drug (producing less antibodies) to a more antigenic drug (producing more antibodies).