Liver Injury Warning for MS Drug Avonex

March 16, 2005 -- Patients taking the multiple sclerosis (MS) drug Avonex should be watched for possible liver problems, says the drug's maker.

Rare cases of severe liver injury, including cases of liver failure, have been reported among Avonex users, says Avonex's maker, Biogen, in a letter to doctors.

"Patients should be monitored for signs of [liver] injury," says the revised Avonex warning label.

Here's how the drug's web site puts it:

"Your liver may be affected by taking Avonex and a few patients have developed severe liver injury. Your healthcare provider may ask you to have regular blood tests to make sure that your liver is working properly. If your skin or the whites of your eyes become yellow or if you are bruising easily you should call your doctor immediately."

Liver Damage Without Symptoms

Liver enzymes can become elevated while taking Avonex. This elevation is a sign of possible liver damage and can be detected on blood tests. However, there are often no symptoms associated with high liver enzymes. Liver enzyme elevation recurred in some patients who tried taking Avonex again.

The findings were seen in postmarketing data, says the Biogen letter. The number of affected patients and details about them were not disclosed.

Some of the cases occurred in Avonex users who were also taking other drugs that could cause liver problems, says the Biogen letter. The potential for liver problems should be weighed when using Avonex with such drugs and products that may affect the liver -- including alcohol.

The same risk should also be considered when adding new treatments to patients already taking Avonex.

Pregnancy and Avonex

Biogen also made another change to Avonex labels. The revision encourages doctors to enroll women who become pregnant while taking Avonex in the Avonex Pregnancy Registry. "Avonex has not been studied in pregnant women," says the drug's web site.

Avonex is used to help treat MS symptoms. It's administered by injection once a week.

In 2003, the FDA approved its use for people who had suffered only one MS attack, as confirmed by brain scans. Avonex was the first drug to get approval for those patients. Previously, it was typically used only for patients who had experienced at least two MS attacks.

The most common side effects associated with Avonex include flu-like symptoms, fever, fatigue, headache, chills, nausea, vomiting, and pain. Cautions for Avonex use have already been noted for people with mood disorders including depression. Patients with heart disease should also be closely monitored while taking Avonex.