Nplate (romiplostim)

The only injectable TPO receptor agonist for ITP. It suits people who prefer not to take a daily pill or struggle with eltrombopag's food and calcium rules, at the cost of a weekly clinic visit.

Romiplostim mimics thrombopoietin (TPO), the hormone that tells cells in the bone marrow to make platelets. It binds the TPO receptor on those cells and turns on the signal, so the marrow makes more platelets. In ITP the immune system destroys platelets faster than the body replaces them; romiplostim raises production enough to keep the count at a safer level rather than stopping the immune attack.

Nplate has no boxed warning. The label warns that in people with myelodysplastic syndromes (MDS), a bone marrow condition, Nplate can raise blast counts and the risk of progressing to acute myeloid leukemia, so it is not used for MDS or any cause of low platelets other than ITP. Higher platelet counts can bring blood clots, including clots in the liver's portal vein in people with chronic liver disease. Platelets can also stay low or fall again during treatment, sometimes because of antibodies to the drug. The most common side effects in adults, against placebo, were joint pain (26% against 20%), dizziness (17% against 0%), trouble sleeping (16% against 7%), muscle pain (14% against 2%), pain in the arms or legs (13% against 5%) and belly pain (11% against 0%). In children the most common were bruising (41%), upper respiratory infection (31%) and mouth and throat pain (25%).

Biologic given weekly in a clinic, so cost depends on medical-benefit coverage as well as copay help. Amgen reports that about 7 in 10 Nplate claims in 2023 to 2024 had $0 out-of-pocket cost across commercial and Medicare plans.

Pick your insurance to see which help fits. Drugmaker copay cards can't be used with Medicare, Medicaid or TRICARE; charity funds are the usual route there.

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Approved for adults with ITP after an insufficient response to corticosteroids, immunoglobulins or splenectomy, and for children 1 year and older who have had ITP for at least 6 months with the same history. Not for MDS or other causes of low platelets.

Source: Amgen SupportPlus for Nplate

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Two 24-week placebo-controlled trials enrolled adults with ITP whose platelet counts were 30,000 or lower after at least 1 earlier treatment. In people who still had their spleen (Study 1, NCT00102336), 61% on Nplate had a durable platelet response against 5% on placebo, and 20% needed rescue treatment against 62%. In people whose spleen had been removed (Study 2, NCT00102323), 38% had a durable response against none on placebo, and 26% needed rescue treatment against 57%.

The FDA approved Nplate on August 22, 2008 for adults with ITP, making it the first TPO receptor agonist approved in the US. Approval for children 1 year and older who have had ITP for at least 6 months followed on December 14, 2018, and approval for acute radiation syndrome on January 28, 2021.

Steroids and IVIG are usually tried first. When they are not enough, options include the TPO receptor agonists Nplate, Promacta and generic eltrombopag, Alvaiz and Doptelet (avatrombopag), which raise platelet production; Tavalisse (fostamatinib) and Wayrilz (rilzabrutinib), which slow platelet destruction; and rituximab or spleen removal.