Thrombopoietin receptor agonists are pharmaceutical agents that stimulate platelet production in the bone marrow. In this, they differ from the previously discussed agents that act by attempting to curtail platelet destruction.
Mode of Action:
Eltrombopag is an orally bioavailable, small-molecule TPO-receptor agonist that interacts with the transmembrane domain of the human TPO-receptor. Eltrombopag is a stimulator of STAT and JAK phosphorylation. Unlike recombinant TPO or romiplostim, Eltrombopag does not activate the AKT pathway in any way. It should be noted that when given to patients with aplastic anemia, other lineages besides platelet count were increased, suggesting that either eltrombopag enhanced the effect of TPO in vivo; or there is a yet uncovered mechanism of action at work.
Eltrombopag is predominantly through pathways including cleavage, oxidation, and conjugation with glucuronic acid, glutathione, or cysteine. In vitro studies suggest that CYP1A2 and CYP2C8 are responsible for the oxidative metabolism of eltrombopag. UGT1A1 and UGT1A3 are responsible for the glucuronidation of eltrombopag.
Eltrombopag may cause hepatotoxicity, especially if administered in combination with interferon and ribavirin in patients with chronic hepatitis C (may increase the risk of hepatic decompensation).
http://www.gsk.com/media/press-releases/2012/FDA-approves-new-indication-for-PROMACTA-eltrombopag.htmlZekry A, Freiman J: Eltrombopag: Is this “24 karat gold platelet” treatment for thrombocytopenia in cirrhosis associated with hepatitis C? Hepatology. 2008 Apr;47(4):1418-21. PubmedMondelli MU: Eltrombopag: An effective remedy for thrombocytopaenia? J Hepatol. 2008 Jun;48(6):1030-2. Epub 2008 Mar 31. PubmedTarantino MD, Fogarty P, Mayer B, Vasey SY, Brainsky A: Efficacy of eltrombopag in management of bleeding symptoms associated with chronic immune thrombocytopenia. Blood Coagul Fibrinolysis. 2013 Apr;24(3):284-96. doi: 10.1097/MBC.0b013e32835fac99. Pubmed 23492914Kiang TK, Ensom MH, Chang TK: UDP-glucuronosyltransferases and clinical drug-drug interactions. Pharmacol Ther. 2005 Apr;106(1):97-132. Epub 2005 Jan 12. PubmedDeng Y, Madatian A, Wire MB, Bowen C, Park JW, Williams D, Peng B, Schubert E, Gorycki F, Levy M, Gorycki PD: Metabolism and disposition of eltrombopag, an oral, nonpeptide thrombopoietin receptor agonist, in healthy human subjects. Drug Metab Dispos. 2011 Sep;39(9):1734-46. doi: 10.1124/dmd.111.040170. Epub 2011 Jun 6. PubmedKuter DJ: The biology of thrombopoietin and thrombopoietin receptor agonists. Int J Hematol. 2013 Jul;98(1):10-23. doi: 10.1007/s12185-013-1382-0. Epub 2013 Jul 3. Pubmed
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