(TPO Receptor Agonists)
Platelet Growth Factors or Thrombopoietin (TPO) receptor agonists are a class of treatments that stimulate the bone marrow to produce more platelets. TPO, a protein made in the liver, naturally stimulates platelet production in the bone marrow. TPO receptor agonists bind to the same receptor as the TPO produced in the body. This prompts the megakaryocytes in the bone marrow to produce more platelets.
While ITP is often considered a disease characterized by platelet destruction, recent research has shown that many people with ITP also have unusually low platelet production. The additional bone marrow stimulation prompted by the TPO receptor agonists creates a sufficient number of platelets to overcome the platelet destruction or platelet production problems in most people who receive these treatments.
romiplostim (Nplate) - Amgen
Romiplostim is a manufactured peptibody (part peptide and part antibody) liquid that is given by weekly subcutaneous (under the skin) injection. On September 4, 2008, the US FDA approved romiplostim for adults with ITP (either splenectomized or not) who have failed at least one other treatment for the disease.
Dose: The dose of romiplostim depends on the patient's weight and response to previous doses. The initial dose is 1 mcg/kg. The dose is reduced or discontinued if the platelet count rises too high or the patient doesn't respond.
Side Effects: The most common adverse reactions are joint and muscle pain, dizziness, insomnia, indigestion, and 'pins and needles' sensation. There is a potential for patients to develop reticulum (fibrous growths) in the bone marrow and also for the platelet count to drop below the pre-treatment count if the treatment is discontinued.
Assistance Programs: Amgen has established several programs to assist those people who are not insured, underinsured or who cannot meet the insurance co-payments. Find more information at the financial support section of the Amgen Web site.
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eltrombopag (Promacta/Revolade) - GlaxoSmithKline
Eltrobopag is a small molecule (pill) taken daily. The drug was given limited approval by the FDA in November, 2008, and full approval in February, 2011, for the treatment of ITP in adults.
Dose: In the initial clinical trials, patients receiving 50 mcg or 75 mcg tablets had the best response. The pill must be taken on an empty stomach as other medications and food affect its absorption.
Side Effects: The most common adverse reaction reported was a mild to moderate headache. Elevated liver functions were present in some research subjects. Cataracts were observed in mice, but not in people.
Assistance Program: GlaxoSmithKline offers payment assistance for their products. For more information see the financial assistance portion of the GSK Web site.
Related Web Sites:
E5501 – Eisai
E5501 (avatrombopag maleate) is a small molecule, once daily pill, that has stimulated platelet production in mice and healthy human subjects. This compound was acquired by Eisai from MGIpharma, and previously, AKArx. Clinical trials for ITP patients are in progress.
LGD4665 – Ligand Pharmaceuticals
Ligand Pharmaceuticals has completed a clinical trail for this once daily pill. This compound has increased platelet counts and had an good safety profile in mice and healthy human subjects. No results have been published.