Rebif Side Effects May Be Linked to Serious Blood Disorder: Report

Doctors from the U.K. are raising concerns about the risk of a serious blood disorder that appears to be linked to side effects of Rebif, a multiple sclerosis drug that may case the development of dangerous blood clots in small blood vessels.

In a letter to the editor published late last month in the New England Journal of Medicine, doctors warn that a surprisingly high number of cases of thrombotic microangiopathy have been seen among users of Rebif. While the condition was originally thought to be rare and not life-threatening, a spike in reports and at least one death have some doctors concerned.

Thrombotic microangiopathy involves cellular damage to blood vessels that can cause blood clots in small blood vessels. Patients suddenly suffer from high blood pressure. The condition is considered a combination of hemolytic-uremic syndrome (HUS), and thrombotic thrombocytopenic purpura (TTP).

HUS results in a sudden decrease in blood platelets, destruction of red blood cells and in about 10% of cases, can cause kidney failure. The destroyed red blood cells can coalesce into blood clots. The clots then cause TTP, which leads to blood clots and reduced blood platelets. TTP can be fatal between 10% and 20% of the time.

The condition has been linked to Rebif in the past, but Merck previously indicated that the blood disorder is rare. The letter indicates that four recently seen cases in South Scotland, and another six cases from across the U.K. represent an unusual spike. The researchers also found at least one fatal complication linked to the problem.

Dr. Siddharthan Chandran, the lead author and a professor of neurology at the University of Edinburgh, wrote that he suspects that there may have been some recent change in the Rebif manufacturing process that may have changed the drug’s safety profile.

The letter follows a warning issued in December by the U.K.’s Medicines and Healthcare Products Regulatory Agency (MHRA), which began investigating a cluster of Rebif thrombotic microangiopathy cases and asked doctors to be vigilant for symptoms and signs among the drug’s users.

Rebif (interferon beta 1-alpha) was first approved or the treatment of multiple sclerosis in Europe in 1996, and then in the U.S. in 2002. It is sold in the U.K. by Merck and in the U.S. by Merck and Pfizer.