The missing piece of the puzzle

All three interferon medications (Avonex®, Betaseron®, and Rebif®) can trigger neutralizing antibodies (NABs). The scientific term for this is "immunogenicity." But it is believed that the three treatments are not equally immunogenic. That is, the chance that NABs will form is different for each interferon. The different immunogenicities of the three interferons have become a key difference among these MS treatments.

In previous studies, 28-43% of people on Betaseron® developed NABs, compared to 12-25% of people on Rebif®. Betaseron® NABs seemed to disappear over time, but it is unknown whether Rebif® NABs do the same. Less than 7% of people taking Avonex® developed NABs. Another way of saying this is that Betaseron® is the most immunogenic interferon, followed by Rebif® and, lastly, Avonex®.

There is no guaranteed way to prevent NABs yet. Some experts say that is best to start people on the least immunogenic interferon so that they're less likely to develop NABs in the first place. The route of administration may also be important, as NAB formation may be decreased with intramuscular injection. Another approach to prevent NABs is to give intravenous corticosteroids, although this would not be recommended on a regular basis without a good reason.

Currently, testing for NABs is not done routinely. Doctors may test for NABs if people are not responding to treatment. However, experts are not convinced of what to do after people test positive for NABs. One option is to stop the interferon medication in people with NABs, wait for the antibodies to disappear, and then start another less immunogenic interferon. Switching interferons without waiting may not be advisable, as NABs can cross-react. Another option may be to increase the dose of interferon. However, this may lead to a serious complication known as immune complex disease (where antibody-interferon clusters get trapped in the kidneys, lungs, skin and joints). Finally, stopping interferon treatment altogether may be an alternative.

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