Effect of interferon (IFN) on refractory idiopathic thrombocytopenic purpura: administration of 6 million units of recombinant IFN alpha-2b.

Five patients (six courses) with refractory idiopathic thrombocytopenic purpura (ITP) were given 6 million units of recombinant interferon (IFN) alpha-2b in 12 doses to achieve an improved response rate compared to previous studies using 3 million units. From the initial IFN administration, the platelet count increased from a pre-treatment level of 20.7 +/- 17.7 x 10(3)/microliters (mean +/- SD) and reached its first peak in weeks 2 or 3 of therapy (p < 0.05). In week 5, the platelet count made its second and maximum peak (66.5 +/- 57.9 x 10(3)/microliters; p < 0.05). A relatively good response of the platelet count (an increase to > 50 x 10(3)/microliters) was observed in three patients (four courses) out of five. These responses were not much faster or more improved than in previous reports, and a dose of 6 million units may be too large to treat some ITP patients. The platelet-associated IgG level showed a tendency to be reduced with IFN therapy. The mechanism for the increase of the platelet count may be the modification of platelet autoantibody production.