Rare, But Serious, Side Effect Reported With One MS Drug

By Serena Gordon HealthDay Reporter

WEDNESDAY, April 2, 2014 (HealthDay News) -- A handful of people taking a medication called Rebif to treat multiple sclerosis have developed a serious condition that causes blood clots to form in small blood vessels throughout the body.

In a letter in the March 27 issue of the New England Journal of Medicine, Scottish researchers reported that they found an unexpectedly high number of cases of "thrombotic microangiopathy" in people taking Rebif who suddenly developed severe high blood pressure. The condition is a combination of the clotting disorders hemolytic-uremic syndrome and thrombotic thrombocytopenic purpura (HUS/TTP).

The two disorders often occur together. In HUS, the red blood cells are destroyed, and the debris from that destruction clumps together and clots. Those numerous blood clots cause TTP, which occurs when small blood vessels throughout the body become blocked with blood clots, according to the U.S. National Library of Medicine.

The clotting condition is a recognized complication of using Rebif, which is one of the brand names for the drug interferon beta 1-alpha, said study senior author Siddharthan Chandran, a professor of neurology at the University of Edinburgh. In fact, British regulatory authorities issued a drug-safety update last December on the heightened risk for the condition, Chandran added.

While Chandran said that Merck, the maker of Rebif, has stated in product labeling that this clotting condition is rare, the researchers suggest that some recent change in the manufacturing process might play a role because these complications haven't been seen thus far in another type of interferon beta 1-alpha.

Two U.S. experts weighed in on the issue.

"The National MS Society's expectation is that regulatory authorities will look into the matter cited in the NEJM letter to determine if there are any additional safety concerns beyond the cautions that already appear on the product's label," said Timothy Coetzee, chief advocacy, services and research officer for the National MS Society.

Dr. Karen Blitz, director of the North Shore-LIJ Multiple Sclerosis Center in East Meadow, N.Y., said medications all have some risks, even aspirin. In this case, she said, "the risk-benefit profile for this drug is still way in favor of the benefits. People with MS who aren't protected by disease-modifying therapy have a higher likelihood of disability."

Interferon beta 1-alpha is believed to help slow the progression of MS if it is given early in the course of the disease and taken long-term. It's what is known as a disease-modifying drug.

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Rare, But Serious, Side Effect Reported With One MS Drug