1. Romiplostim(DB05332) Approved Drug
Chemical Formula: C2634H4086N722O790S18
Molecular Weight: 59 kDa
Romiplostim is a thrombopoiesis stimulating dimer Fc-peptide fusion protein (peptibody) to increase platelet production through activation of the thrombopoietin receptor. The peptibody molecule has two identical single-chain subunits, each one is made up of 269 amino acid residues. Each subunit consists of an IgG1 Fc carrier domain that is covalently attached to a polypeptide sequence that contains two binding domains to interact with thrombopoietin receptor c-Mpl. Each domain consists of 14 amino acids. Interestingly, romiplostim's amino acid sequence is not similar to that of endogenous thrombopoietin. Romiplostim is produced by recombinant DNA technology in Escherichia coli. FDA approved on August 22, 2008.
Indication/Usage
Treatment of chronic immune thrombocytopenic purpura.
Pharmacodynamics
Responses to platelet increase varies between patients thus indicating a need for individualization of dose. However, a dose dependent-increase in platelet counts have been observed in clinical trials. Does not affect platelet destruction.

2. Volume of Distribution
Mechanism of Action
Romiplostim is a thrombopoietin receptor agonist that activates intracellular transcriptional pathways via c-Mpl to increase production of platelets. It also works similarly to thrombopoietin (TPO), an endogenous glycoprotein hormone that regulates the production of platelets in the bone marrow.
Toxicity
The most common adverse reactions (5% higher patient incidence in Nplate versus placebo) are arthralgia, dizziness, insomnia, myalgia, pain in extremity, abdominal pain, shoulder pain, dyspepsia, and paresthesia. Headache was the most commonly reported adverse reaction that did not occur at 5% higher patient incidence in Nplate versus placebo. LD50 = 980 mg/kg.
Absorption
Cmax, healthy volunteers, subQ = hours; Cmax, immune thrombocytopenia patients, subQ = 7-50 hours (median = 14 hours). Not affected by age, weight, or gender. Accumulation does not occur after six weekly doses of 3 mcg/kg romiplostim.
Half- Life
Immune thrombocytopenia patients, subQ = 3.5 days (median) (range 1-34 days)
Route of Elimination
Renal clearance (more dominant mode of clearance as dose increases) and binding to c-Mpl receptors (dominant mode of clearance at low doses)
Volume of Distribution
In healthy volunteers, non-linear decrease in Vd with increase IV dose of romiplostim which indicates saturation of c-Mpl receptors. Vd, 0.3 g/kg = 122 mL/kg; Vd, 10 g/kg = 48.2 mL/kg
Category
Colony-Stimulating Factors and Thrombopoietic Agents

3. Affected Organisms Sequence Target General References Brands
Human and other Mammals
Sequence
MDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGKGGGGGIEGPTLRQWLAARAGGGGGGGGIEGPTLRQWLAARA
Target
Thrombopoietin Receptor
General References
Kumagai Y, Fujita T, Ozaki M, Sahashi K, Ohkura M, Ohtsu T, Arai Y, Sonehara Y, Nichol JL: Pharmacodynamics and Pharmacokinetics of AMG 531, a Thrombopoiesis-Stimulating Peptibody, in Healthy Japanese Subjects: A Randomized, Placebo-Controlled Study. J Clin Pharmacol Dec;47(12): Epub 2007 Oct 9. "Pubmed":
Rice L: Drug evaluation: AMG-531 for the treatment of thrombocytopenias. Curr Opin Investig Drugs Sep;7(9): "Pubmed":
Keating GM: Romiplostim: a review of its use in immune thrombocytopenia. Drugs Feb 12;72(3): doi: /
"Pubmed":
FDA label#
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Brands
Nplate- Amgen Inc

4. Nplate Formulation Used/Prescribed for Dosage
Romiplostim, a member of the TPO mimetic class, is an Fc-peptide fusion protein (peptibody) that activates intracellular transcriptional pathways leading to increased platelet production via the TPO receptor (also known as cMpl). The peptibody molecule contains two identical single-chain subunits, each consisting of human immunoglobulin IgG1 Fc domain, covalently linked at the C-terminus to a peptide containing two thrombopoietin receptor-binding domains. Romiplostim has no amino acid sequence homology to endogenousTPO. Nplate is supplied as a sterile, preservative-free, lyophilized, solid white powder to be administered as subcutaneous injection
Formulation
Two vial presentations are available, which contain a sufficient amount of active ingredient to provide either 250 mcg or 500 mcg of deliverable romiplostim, respectively. Each single-use 250 mcg vial of Nplate contains the following: 375 mcg romiplostim, 30 mg mannitol, 15 mg sucrose, 1.2 mg L-histidine, 0.03 mg polysorbate 20, and sufficient HCl to adjust the pH to a target of 5.0. Each single-use 500 mcg vial of Nplate contains the following: 625 mcg romiplostim, 50 mg mannitol, 25 mg sucrose, 1.9 mg L-histidine, 0.05 mg polysorbate 20, and sufficient HCl to adjust the pH to a target of 5.0
Used/Prescribed for
Nplate is indicated for the treatment of thrombocytopenia in patients with chronic immune thrombocytopenia (ITP) who have had an insufficient response to corticosteroids, immunoglobulins or splenectomy.
Dosage
The initial dose for Nplate is 1 mcg/kg based on actual body weight, If the platelet count is < 50 x 109/L, increase the dose by 1 mcg/kg, If platelet count is > 200 x 109/L for 2 consecutive weeks, reduce the dose by 1 mcg/kg., If platelet count is > 400 x 109/L, do not dose. Continue to assess the platelet count weekly. After the platelet count has fallen to < 200 x 109/L, resume Nplate at a dose reduced by 1 mcg/kg.

5. Contraindications Side- effects Drug Interactions References None
Progression of Myelodysplastic Syndromes, Thrombotic/Thromboembolic Complications, Loss of Response to Nplate, Laboratory Monitoring, Erythromelalgia, Hypersensitivity, Angioedema
Drug Interactions
No formal drug interaction studies of Nplate have been performed..
References