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How to Prescribe Interferon beta-1a: Avonex®

James Bowen, MD

Medical Director, Multiple Sclerosis Center

Swedish Neuroscience Institute

Seattle, WA



  • Slows the course of multiple sclerosis when used regularly over long periods of time.
  • Does not improve existing symptoms.
  • Is not used to treat acute MS attacks.


Generic name: interferon beta-1a


How supplied: AvonexÒ comes in prepackaged kits containing all needed supplies. It comes in either prefilled syringes with 30 mcg, or in vials of lyophilized powder with 33 mcg. There are four doses per package.


Initial dose: AvonexÒ should be started at 1/4 dose and tapered upwards as tolerated. Most patients tolerate an increase of ¼ dose every two weeks. These doses are obtained by removing some of the fluid from the syringe. The time of day does not matter, though most patients find that the flu-like side effects are better tolerated if the medication is given at bedtime.


Maintenance dose: 30mcg intramuscularly once a week.


Antipyretics: Antipyretics should be prescribed for every patient starting AvonexÒ. Flu-like side effects usually begin about an hour after the injection, so the antipyretics can be administered at the time of the injection. Typical medications include: acetaminophen 650mg qid, aspirin 650mg qid, ibuprofen 600mg tid, or naproxen 250mg bid. In cases with refractory flu-like side effects, acetaminophen can be combined with either aspirin, ibuprofen, or naproxen. Flu-like side effects may also be decreased with pentoxifylline 400mg tid, or with prednisone 20mg po given with each injection. Antipyretics may be needed only at the time of the injection or they may also be needed the following day. Over time, antipyretics may be tapered or discontinued as tolerated.


Sharps container: Sharps containers for needle disposal should be prescribed.


Autoinjector: Pen injector available soon through pharmacy.


Initial training: Initial training for patients is provided by the manufacturer (Biogen Idec) through visiting nurse services. This may be arranged by contacting MS Active Source at 1-800-456-2255. Larger centers may perform their own training.


Laboratory testing: Basic chemistry panels, transaminases, and CBCs should be monitored. These should be checked before initiating treatment, and at 1, 3, and 6 months after starting treatment. After 6 months they should be checked periodically. Thyroid function tests are recommended every 6 months for those with thyroid dysfunction.


Side effects:

  • Flu-like side effects (fever, myalgias) should be treated with antipyretics (see above). Flu-like side effects typically lessen over the first few months of use.
  • Depression. Whether AvonexÒ causes depression is uncertain. Patients should be monitored and treated appropriately should depression develop.
  • Transaminase elevation may occasionally occur. Elevations up to three times normal may be followed. Elevations above three times normal should be treated with dose reduction. Once transaminases have improved the dose can be gradually increased.
  • Mild leucopenia may be followed. Severe leucopenia usually responds to dose reduction.


Company Support:   MS Active Source - 1-800-456-2255.




Last Updated: April 2012