Avonex, Betaseron, Extavia, Plegridy and Rebif are interferon therapies. Interferon is a natural compound that our immune cells make. Interferon treatment can help “quiet down” inflammatory white blood cells and help block these cells from crossing the blood vessel walls into the brain and spinal cord. Fortunately, this anti-inflammatory benefit does not result in increased infections.

Avonex, Plegridy and Rebif

Three interferon beta-1a options are available, Avonex, Plegridy and Rebif. Avonex is given as 30 micrograms in the muscle once a week and Rebif is given as 44 micrograms under the skin three times a week. Both medications have been shown to prevent relapses, prevent disability and reduce MRI activity. Avonex reduced relapses by 18-32% in clinical trial. In the patients that finished the two year trial, Avonex prevented the likelihood of disability progression by 37%. Rebif reduced relapses by 32%, reduced new MRI activity by 78%, and prevented the likelihood of disability progression by 30% in clinical trial. Interferon side effects and risks include low white blood count, rare liver injury, depression, injection reactions and flu-like symptoms that are generally manageable and improve over the first 1-2 months.

In the Evidence trial, patients on Rebif had 17% less relapses and 36% less MRI activity at 64 weeks compared to Avonex. However, 25% of Rebif and 2% of Avonex patients developed antibodies to the interferon which might cause the medication to become less effective. Rebif caused less flu-like symptoms than Avonex, but more liver and white blood count test abnormalities.

Plegridy, approved in August 2014, has a pegylated tail added to the interferon molecule so injection under skin can be given only once every 2 weeks. In the ADVANCE Trial, 512 patients received 125 micrograms of Plegridy and 500 patients received placebo every 14 days under the skin over 48 weeks. MS attacks (annualized relapse rate) dropped by 36%. Risk of disability progression was reduced by 38%. Sixty-seven percent less new or enlarging T2 lesions and 86% less contrast-enhancing T1 lesions.


Betaseron is a slightly different interferon, interferon beta-1b. Betaseron is given under the skin every other day. Betaseron has also been shown to prevent 34% of relapses and reduce new MRI activity 83%. Trials have also shown that Betaseron reduces the likelihood of becoming disabled when initiated after the first attack and even if secondary progressive with relapses. A head-to-head trial showed benefit of Betaseron over Avonex on relapses, disability and MRI, but the trial was partially limited because both the patients and treating doctors knew which medication the patient was taking (“unblinded”). However, the MRI data was “blinded.”


Extavia is interferon beta-1b. Interferon beta-1b was the first FDA-approved treatment in 1993. The version of interferon beta-1b available for the past 16 years has been Betaseron. Novartis, who temporarily owned the plant making interferon beta-1b, has made an arrangement with Bayer, makers of Betaseron, to brand and market their version Extavia.