Interferon beta-1a is used to treat relapsing forms of multiple sclerosis in adults (including clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease).

This medicine will not cure MS, it will only decrease the frequency of relapse symptoms.

Interferon beta-1a may also be used for purposes not listed in this medication guide.

You should not use this medicine if you are allergic to natural or recombinant interferon beta or albumin.

Tell your doctor if you have ever had:

• bleeding problems or a blood clot;
• depression, mental illness, or suicidal thoughts or actions;
• liver disease;
• bleeding problems;
• low blood cell counts;
• heart disease;
• a thyroid disorder;
• a latex allergy;
• an autoimmune disorder such as rheumatoid arthritis, lupus, or psoriasis;
• a seizure; or
• if you drink alcohol.

Some brands of interferon beta-1a contain donated human plasma and may contain viruses or other infectious agents. Donated plasma is tested and treated to reduce the risk of contamination, but there is still a small possibility it could transmit disease. Ask your doctor about any possible risk.

Tell your doctor if you are pregnant or plan to become pregnant, or if you are breastfeeding.

Interferon beta-1a is not approved for use by anyone younger than 18 years old.

Use Interferon Beta-1A (Avonex) exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.

Get emergency medical help if you have signs of an allergic reaction (hives, itching, anxiety, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Interferon beta-1a can cause life-threatening blood clots in the small blood vessels inside your organs, such as your brain or kidneys. Seek medical help right away if you have symptoms of this condition, such as a fever, tiredness, decreased urination, bruising, or nosebleeds.

Call your doctor at once if you have:

• pain, swelling, bruising, redness, oozing, or skin changes where the injection was given;
• a light-headed feeling, like you might pass out;
• unusual changes in mood or behavior (feeling hopeless, anxious, nervous, irritable, or depressed);
• thoughts about suicide or hurting yourself;
• easy bruising, unusual bleeding;
• a seizure;
• heart problems--swelling, rapid weight gain, feeling short of breath, rapid heartbeats, chest pain spreading to your jaw or shoulder, nausea, sweating;
• liver problems--nausea, loss of appetite, tiredness, confusion, easy bruising or bleeding, dark urine, clay-colored stools, or jaundice (yellowing of your skin or eyes);
• signs of infection--fever, chills, cough with mucus, bloody diarrhea, pain or burning when you urinate; or
• thyroid problems--mood swings, trouble sleeping, tiredness, hunger, diarrhea, pounding heartbeats, muscle weakness, sweating, dry skin, thinning hair, menstrual changes, weight changes, puffiness in your face, feeling more sensitive to hot or cold temperatures.

Common side effects may include:

• low blood cell counts;
• skin changes where the injection was given;
• depression;
• abnormal liver function tests;
• stomach pain; or
• flu symptoms--headache, fever, chills, chest pain, back pain, tiredness, weakness, muscle aches.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Avoid injecting this medicine into skin that is red, bruised, irritated, scarred, or infected.