Neutralizing antibodies (NAbs) can make your MS medication less effective. Could you be at risk of developing NAbs?
There's no way to tell for sure who will develop NAbs to their MS medication. Anyone taking a disease-modifying medication for MS could potentially develop NAbs. But there are a few things that can increase the chances of NAbs:
- Being on treatment for more than 12-18 months: NAbs usually start to appear after 12-18 months of treatment.
- Dosage: higher doses may increase the risk of NAbs for some medications.
- How often the medication is used: More frequent use (for example, three times a week versus once weekly) can increase the risk of NAbs for some medications.
Although the things listed above can increase the risk of NAbs, this does not mean that you should change a treatment that is working for you because you are worried about developing NAbs. Most people never develop NAbs, and of those who do, not all experience a loss of effectiveness in their treatment. Talk to your doctor for further guidance if you are concerned about NAbs.
The medication you're taking can also make a difference. Each of the interferon medications has a different risk of developing NAbs. In two studies designed to compare the rates of NAbs between the three medications:
- Avonex® (interferon beta-1a once weekly) had the lowest risk of NAbs, with a rate of 2-7%.
- Rebif® (interferon beta-1a three times weekly) had a 15-18% risk of NAbs.
- Betaseron® (interferon beta-1b) had a 31-38% risk of developing NAbs.
It's not clear exactly why the risk is lowest with Avonex, but it is believed that this may be related to the structure of the medications, the dose, the way the medications are manufactured, the route of injection (under the skin vs. into a muscle), or how often they're used.
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