Drug counters severe platelet shortage

From San Diego, at a meeting of the American Society of Hematology

People with a condition called immune thrombocytopenic purpura (ITP) make antibodies that destroy platelets, which are required for blood to clot. Because of their platelet shortages, ITP patients live in fear of bumps and scrapes and “can’t even get their teeth cleaned” for fear of a bleeding episode, says David J. Kuter of Massachusetts General Hospital in Boston. Drugs such as steroids offer some relief against this autoimmune disease, but they cause side effects.

Kuter and his colleagues report that an experimental drug designated as AMG531, which is made by Amgen of Thousand Oaks, Calif., revs up production of platelets so that people with ITP can maintain their platelet counts close to the normal range.

The researchers gave 16 ITP patients weekly injections of various doses of the new drug for 6 weeks, while four other ITP patients got placebo shots. The volunteers had entered the study with platelet counts of less than 50,000/microliter of blood. By the end of the 6 weeks, platelet counts had risen to an average of 135,000/µl in people getting a small dose of the drug and 265,000/µl in people getting a larger dose, Kuter says. The range for healthy people is 150,000 to 400,000 platelets per µl.

Study participants receiving placebo injections saw no improvement but have since been given the option of receiving AMG531.

“This has led to a paradigm shift in the treatment of ITP,” says study collaborator James N. George of the University of Oklahoma Health Sciences Center in Oklahoma City. Whereas doctors previously had tried to beat ITP by using powerful steroids to suppress the autoimmune reaction against platelets, the new approach induces the body to make platelets faster than they are being destroyed, he says.

ITP affects roughly 30,000 people in the United States. Researchers already are recruiting ITP patients for a large-scale trial aimed at getting regulatory approval for AMG531.