lthy volunteers -- developed antibodies to the drug, and these antibodies cross-reacted with their own natural thrombopoietin. The result was chronic low platelet counts in people who, in many cases, had never had such problems before," Dr. Bussel says.
The trick, then, was to find a platelet-stimulating agent that avoided this dangerous immune-system response.
"Luckily, Amgen, the company that has funded this research, didn't throw in the towel," Dr. Bussel says.
The company, under the guidance of the study's senior author, Dr. Janet Nichol, eventually developed AMG 531 -- a novel protein with no structural similarity to human thrombopoietin. This dissimilarity and other features mean AMG 531 is largely ignored by the immune system.
The new, two-phase trial was led by Dr. Bussel and conducted at nine centers across the United States.
In the Phase 1 part of the study, doctors first gave six groups of four ITP patients (24 total) two subcutaneous injections of AMG 531 delivered at least two weeks apart. Depending on the group they were in, patients received anywhere from 0.2 to 10 micrograms of the drug per kilogram of body weight.
In the Phase 2 part of the trial, 21 patients were randomized to receive six weekly injections of either a harmless placebo, or AMG 531 at doses of 1, 3, or 6 micrograms per kilogram of body weight.
The Phase 1 results showed the drug to be safe, with no major adverse events attributed to AMG 531 during the treatment period. Four of a total of 41 patients did show some temporary post-treatment lowering of their platelet counts, but this later resolved.
The drug's efficacy impressed the researchers.
"We were very pleased," says Dr. Bussel. Hoping to boost platelet counts to between 50,000 to 450,000 per cubic millimeter, the researchers report that seven of 12 patients given higher doses of AMG 531 (3, 6 or 10 micrograms/kilogram) fePage: 1 2 3 Related medicine news :1
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