In a letter in the March 27th issue of the New England Journal of Medicine, Scottish researchers announced that they’d found evidence linking the MS drug Rebif to the formation of “thrombotic microangiopathy.” This condition causes serious blood clots to form in small blood vessels in different parts of the body. The condition is rare, but it is potentially life threatening.
In the letter to the Journal, researchers said a large number of individuals taking the Rebif drug quickly developed dangerously high blood pressure. Many of those cases were associated with thrombotic microangiopathy, which is caused by a combination of two clotting disorders: hemolytic-uremic syndrome (HUS) and thrombocytopenic purpura (TTP). In HUS, red blood cells are destroyed, resulting in the build-up of debris and the formation of blood clots. Those blood clots then block numerous small blood vessels in the body, causing TTP and a rise in blood pressure.
The clotting condition has been recognized as a complication associated with Rebif, the study’s senior author, Siddharthan Chandran said. In fact, British regulatory authorities did issue a safety update in December to warn users about the risk for the condition. Chandran, said it isn't clear why the complication occurs in some patients. “The mechanism that triggers this complication is not fully understood, and more research is needed into the relationship between interferon beta and thrombotic microangiopathy,” said Chandran.
However, there are some suspicions that these complications may be rooted in some recent changes to the drug’s manufacturing process. These questions arise because these complications haven’t been seen in another type of the drug interferon beta-1 alpha.
U.S. experts expect regulatory agencies to take a closer look at the MS drug. Timothy Coetzee, the chief advocacy and research officer for the National MS Society, said, “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.”
Interferon beta 1-alpha is a disease-modifying drug, which, if given early enough in the course of the disease and taken long term, is expected to slow the progression of MS. During the first 9 years of safety monitoring for Rebif — one of the brand names for the drug interferon beta-1 alpha — there were very few cases of the serious clotting conditions. There were four cases of the clotting condition. All four of these patients had been taking Rebif long-term and had been tolerating the drug well. Of these four, three were found to have been newly diagnosed with high blood pressure. Impaired kidney function and abnormalities in the blood are potential early warning signs of the blood clot complication, Chandran said.