New Drugs for ITP

The world of platelets and ITP has gone through some changes lately with the approval of two new drugs for ITP and the presentation of data on the use of established drug rituximab (Rituxan) for ITP at the recent American Society of Hematology (ASH) annual meeting earlier this month.

Approval of Nplate (romiplostim)(Amgen) came in August of this year, while approval of Promacta (eltrombopag) (GSK) came in in November. The main practical difference between these drugs is that Nplate is administered subcutaneously on a weekly schedule, while Promacta is given orally on a daily basis..

Both Nplate and Promacta have indications for patients with chronic immune thrombocytopenic purpura (ITP) who have had an insufficient response to corticosteroids, immunoglobulins, or splenectomy. Both drugs are thrombopoietin (TPO) receptor agonists that stimulate bone marrow megakaryocytes to produce platelets.

Areas of concern about these drugs have to do with increased reticulin formation and fibrosis in the bone marrow, thrombogenic potential from too high an increase in platelets, and possible malignant transformation to leukemia, especially in myelodysplastic disorders (MDS). Also, discontinuation of drug may cause rebound thrombocytopenia.

Although Nplate was the first to receive approval, it is my guess that Promacta will be more widely used given its oral availability. However, cost of both of these new drugs could limit their use. And, given that ITP is relatively uncommon, it is my guess that these drugs may try to find broader use in other situations, such as chemotherapy induced thrombocytopenias, MDS and chronic thrombocytopenia from hypersplenism due to chronic liver disease. The market potential in these situations is much larger.

In other news, the combination of Rituxan plus dexamethasone was reported by Italian investigators to be significantly better in inducing initial and sustained responses in patients with ITP than dexamethasone alone, in a plenary session abstract presented at the ASH annual meeting. It was concluded that the option of treatment with Rituxan plus dexamethasone could be offered as an option before splenectomy, particularly in patients who are at high risk of complications from surgery or who are reluctant to undergo splenectomy.