|Trade names||Nplate, Romiplate|
|Drug class||Colony-stimulating factor|
|Main uses||Immune thrombocytopenic purpura (ITP), acute radiation syndrome|
|Side effects||Joint pain, trouble sleeping, abdominal pain, headache, tiredness|
|Elimination half-life||1 to 34 days|
|Chemical and physical data|
|Molar mass||59085.01 g·mol−1|
Romiplostim, sold under the brand name Nplate among others, is a medication used to treat immune thrombocytopenic purpura (ITP) and acute radiation syndrome. In ITP it may be used when corticosteroids, immunoglobulins, or splenectomy are not effective. It is given by injection under the skin.
Common side effects include joint pain, trouble sleeping, abdominal pain, headache, and tiredness. Other side effects include blood cancer, blood clots, and bone marrow fibrosis. Safety in pregnancy is unclear. It works to stimulate platelet production by activating the thrombopoietin receptor.
Romiplostim was approved for medical use in the United States in 2008 and Europe in 2009. In the United Kingdom a 125 mcg vial costs the NHS about £240 as of 2021. This amount in the United States costs about 1,100 USD.
Romiplostim is indicated as a potential treatment for chronic idiopathic (immune) thrombocytopenic purpura (ITP). Romiplostim was designated an orphan drug by the U.S. Food and Drug Administration (FDA) in 2003, as the chronic ITP population in the USA is under 200,000 (the chronic adult ITP population in the USA is thought to be around 60,000, with women outnumbering men by a factor of two). The wholesale cost of romiplostim if administered weekly is currently estimated at US$55,250 per year.
On August 22, 2008, the FDA approved romiplostim as a long-term treatment for chronic ITP in adults who have not responded to other treatments, such as corticosteroids, intravenous immunoglobulin, Rho(D) immune globulin or splenectomy.
In a, 24-week, Phase III trials, romiplostim was more effective than placebo in achieving the primary endpoint of a durable platelet response in nonsplenectomized or splenectomized adults with chronic immune thrombocytopenic purpura.
Romiplostim treatment is generally administered at weekly intervals via subcutaneous injection. Often an initial dose of 1 mcg/kg is used for ITP. For radiation sickness a dose of 10 mcg/kg may be used.
Prior to injection, a complete blood count (CBC) is obtained, as the dosage is dependent on the individual's body weight and platelet count at the time of treatment. The goal of treatment is to maintain the count above 50,000 per cubic millimeter (mm3) of blood, not to achieve a normal count—defined as 150,000–450,000 per mm3 in most healthy individuals. If a count of 200,000 or higher is achieved for two consecutive weeks a reduced dose is administered or treatment is suspended until the count decreases below 200,000. Discontinuation of romiplostim must be approached with great caution, as a rapid decrease in the platelet count may occur, possibly leading to bleeding diathesis.
Romiplostim's effect is to stimulate the patient's megakaryocytes to produce platelets at a more rapid than normal rate, thus overwhelming the immune system's ability to destroy them. As doing so involves changes to the bone marrow chemistry, a number of potentially serious side-effects may develop, including death, myalgia, joint and extremity discomfort, insomnia, thrombocytosis, which may lead to potentially fatal clots, and bone marrow fibrosis, the latter of which may result in an unsafe decrease in the red blood count.
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