Ingredient in New MS Drug Linked to Serious Brain Disease

Reports found four psoriasis patients who took similar drug developed rare but sometimes deadly condition

By Brenda Goodman

HealthDay Reporter

WEDNESDAY, April 24 (HealthDay News) -- The active ingredient in a drug that's expected to become a popular treatment for multiple sclerosis has been linked to four European cases of a rare but sometimes fatal brain disease called progressive multifocal leukoencephalopathy (PML).

The ingredient, dimethyl fumarate, is used in a drug called Fumaderm that was approved in Germany in 1994 to treat the skin condition psoriasis. It is also in a different but closely related medication called Tecfidera, which was just approved by the U.S. Food and Drug Administration in March for the treatment of multiple sclerosis (MS). It is known as a fumaric acid ester, which is commonly used as a food additive and has been used to treat psoriasis in Germany for 30 years.

According to reports published in the April 25 issue of the New England Journal of Medicine, however, four patients who were taking Fumaderm to treat their psoriasis developed PML.

In a letter responding to the reports, Biogen, the company that makes both drugs, said Tecfidera may be safer because it contains only dimethyl fumarate, while Fumaderm also contains three other fumaric acid esters.

The company also noted that none of the patients taking Tecfidera during clinical trials (then known as BG-12) developed PML. Since Tecfidera is a pill rather than an injection, and was effective and well-tolerated by patients in clinical trials, analysts have predicted it would soon become the top-selling multiple sclerosis treatment.

But the German doctor who treated one of the psoriasis patients who got PML thinks there is still cause for concern.

Dr. Jorg Schulz, a neurologist at Rheinisch-Westfaelische Technische Hochschule Aachen, a research university in Aachen, said the two drugs are virtually identical once they are broken down in the body.

"The problem is that the studies with BG-12 covered a two-year period, but no longer periods," Schulz said, and he believes it may take prolonged treatment with the drug for PML to surface.

"With the publication of our case, we wish to create awareness that treatment with any form of fumaric acid may bear the risk of developing PML," Schulz said.

PML is caused by the JC virus, which normally lies dormant in the body and causes no harm. About half of multiple sclerosis patients have antibodies to the JC virus in their blood, suggesting a current or former infection. When the immune system is depleted by illnesses like cancer or AIDS or suppressed by certain medications, the virus can flare and destroy nerve cells in the brain.

Ironically, PML is a lot like multiple sclerosis, but it progresses more rapidly as it causes weakness, paralysis, confusion, memory loss and loss of vision or speech. Quick treatment can stop the damage, although patients may be permanently disabled.

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