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ADVANCES IN THE DIAGNOSIS AND TREATMENT OF THROMBOCYTOPENIA

ADVANCES IN THE DIAGNOSIS AND TREATMENT OF THROMBOCYTOPENIA. Petechiae. Remove Antigen: Rx Inciting Agent = Fix “ITP”. HIV. Hepatitis C. Helicobacter pylori. WHEN TO DO A BONE MARROW IN THE THROMBOCYTOPENIC PATIENT?. ITP: A SIMPLE DISEASE.

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ADVANCES IN THE DIAGNOSIS AND TREATMENT OF THROMBOCYTOPENIA

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  1. ADVANCES IN THE DIAGNOSIS AND TREATMENT OF THROMBOCYTOPENIA

  2. Petechiae

  3. Remove Antigen: Rx Inciting Agent = Fix “ITP” HIV Hepatitis C Helicobacter pylori

  4. WHEN TO DO A BONE MARROW IN THE THROMBOCYTOPENIC PATIENT?

  5. ITP: A SIMPLE DISEASE • Patients make auto-antibodies directed against their own platelets • These platelets are rapidly destroyed • If the platelet count becomes low enough, bleeding symptoms may ensue • Bleeding is rarely serious, ie an intracranial hemorrhage, even at very low counts

  6. ITP: A COMPLICATED DISEASE • Anti-platelet antibodies have not been able to be measured discriminatively: the diagnosis and prognosis (outcome, risk of bleeding) remain insecure • Patients may not make platelets well • Treatment is uncertain: who needs it, what to treat with and in which order

  7. Pathophysiology of ITP Implications for Diagnosis and Treatment

  8. Effect on the Platelet Count of Plasma : ITP into Normal 1000 800 600 400 200 Disease incidence (thousands) 1 2 3 1 2 3 4 5 6 7 8 9 Hours Days Harrington WJ, et al. J. Lab Clin Med. 1951;38:1-10.

  9. ITP: what tests are helpful • Complete CBC---not just the platelets • Bone marrow---not in all/most cases • Blood type & DAT-prognostic re hemolysis • PT-PTT, Thyroid, Ig’s, lupus, SMA • Anti-phospholipid antibodies • Platelet turnover (estimates): platelet retics, thrombopoietin, large platelets

  10. Who Needs Treatment with ITP?At What Platelet Count ? Needs to be individualized: job physical trauma ie sports access to care anxiety effect on fatigue

  11. Acute Platelet Increase • gold standard: IVIG at 1 gm/kg • IV anti-D: as fast as IVIG at 75 mcg/kg • Steroids: IV solumedrol 30/kg, high dose dexamethasone or Prednisone 2-4/kg • Platelet transfusions • Combinations including Steroids, IVIG, IV anti-D and/or vincristine

  12. Advantages and Disadvantages of Treatment for Children with ITP AdvantagesDisadvantages • Steroids: oral, continuous so much toxicity often works with any usage • IVIG: rapid substantial blood product, platelet increase headache, 4-6hrs • IV anti-D: 5-15 minute, at fever-chill, hemo- 75 mcg/kg=IVIG lysis, IVH, blood

  13. STUDY TREATMENTS ARM - A D D D D days 1 2 3 4 7 14 21 28 ARM - B RTX RTX D D D D RTX RTX days 1 2 3 4 7 14 21 28 D: Dexamethasone 40 mg po daily x 4 RTX: Rituximab 375 mg/m2 IV x 4 ML18542 study Clinica Ematologica-Udine

  14. SPLENECTOMY

  15. CONCLUSION: ITP IN CHILDHOOD • Treatment is indicated for those at risk of (serious) bleeding • Choice of treatment needs to be appropriate for the goal: acute vs cure • New treatments will revolutionize care • Understanding of pt pathophysiology may allow individualization of care

  16. GUIDELINES FOR PLATELET TRANSFUSIONS“SAVE ‘EM TIL YOU REALLY NEED ‘EM”NEVER TRANSFUSE A NUMBER.ALWAYS TRANSFUSE A PATIENT!

  17. Platelet Production Is Suboptimal in ITP Patients Autoantibodies inhibit Mk growth and promote apoptosis (Chang, McMillan) Autologous 111In-platelet studies show platelet production < normal in 2/3 pts----same results with absolute platelet retics TPO levels normal in 75% of ITP patients (relative TPO deficiency) Damaged or Dysfunctional Mk in marrow (Houwerijl)

  18. Pathophysiology of ITP Macrophage P Thrombo-poietin Peripheral blood P P Bone marrow P Platelet Megakaryocyte

  19. TPO Agonists in Thrombocytopenic States: Focus on ITP Newer agents that will probably revolutionize our approach to thrombocytopenia in many conditions, not only ITP

  20. rhTPO and PEG-rHUMGDF • rhTPO • Glycosylated • Full length • PEG-rHuMGDF • Not glycosylated • Truncated • Additional polyethylene • glycol moiety COOH terminal domain Polyethylene glycol COOH NH2 NH2 Mpl-binding domain Mpl-binding domain Kuter DJ, Begley CG, Blood 2002;100:3457.

  21. Why Are We Not Using the 1st Generation Thrombopoietins? Initial use of MGDF (and also rhuTPO) resulted in the development of antibodies to exogenous (administered) 1st generation TPO’s that cross-reacted with endogenous TPO (native eTPO): a number of multiply-dosed recipients developed a lasting thrombocytopenia.

  22. TPO Agonist TPO Agonist Fc Fc Carrier Domain Carrier Domain Peptides Peptides AMG 531 • Unique platform “peptibody” • Made in E. coli • Molecular weight = 60,000 D • 4 Mpl binding sites • No sequence homology with TPO • Cleared endothelial FcRn • Recycled • Cleared RES Bussel JB et al. N Engl J Med. 2006;355:1672.

  23. Romiplostim: 38% Durable Response, 79% Overall Response Placebo 20 Romiplostim 15 10 5 0 Overall Response Number of Weeks Platelet Response DurableResponse 100 100 78.6 80 80 12.3 (1.2) 60 60 Mean (SE) Number of Weeks With Platelet Response Durable Platelet Response (%) Overall Platelet Response (%) 38.1 40 40 20 20 0.2 (0.1) 0.0 0.0 0 0 (P < 0.0001) (P = 0.0013) (P < 0.0001) Platelet response: platelet count ≥ 50 x 109/L Durable platelet response: platelet response for ≥ 6 weeks of final 8 weeks,in the absence of rescue medications during 24 week trial Overall response: either durable or transient platelet response (≥ 4 weekly platelet responses) Error bars represent standard deviation of the mean

  24. Romiplostim (AMG 531): Summary In splenectomized patients: 38% durable response, 79% overall response Increased and maintained platelet counts over24 weeks Significantly decreased the use of rescue medications All romiplostim patients discontinued or reduced concurrent ITP therapy (corticosteroids, azathioprine, danazol) Romiplostim appeared to be well tolerated

  25. Romiplostim: Summary of Long-term Dosing Efficacy Data Summary The majority of patients achieved long-term platelet counts > 50 x 109/L and double the baseline value Mean platelet count maintained between 50 and 250 x 109/L over 2 years Use of concomitant and rescue medications was substantially reduced over time No trend in this study for adverse events to increase in frequency with longer drug exposure One patient had neutralizing antibodies to AMG 531; negative on retesting

  26. Eltrombopag: Oral Platelet Growth Factor • Small molecule, non-peptide thrombopoietin receptor (TPO-R) agonist • Does not compete with TPO for binding to TPO-R • Low immunogenic potential • Active only in humans, chimps • Stimulates megakaryocyte proliferation and differentiation • Orally bioavailable • Increases platelet counts in normal volunteers Eltrombopag MW 442 Thrombopoietin MW 64,000

  27. Primary Endpoint: Percentage of Patients With Platelets ≥50,000/µL at Day 43 Visit† P <0.001‡OR = 9.61 (3.31, 27.86) Responders (%) Placebo§ Eltrombopag †Last observation carried forward. ‡Indicates significance at 5% (2-sided) level of significance.§1 patient received IVIg on Day 1. Logistic regression analysis adjusted for randomization stratification variables.

  28. Median Platelet Counts (25th and 75th Percentiles) Baseline to Week 20 350 300 200 150 250 100 50 0 20 33 107 106 106 99 97 92 90 83 76 67 62 65 60 51 55 48 39 43 42 39 Baseline 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Week Number of subjects: Platelet count (Gi/L) Splenectomized pts respond as well as non-splenectomized pts

  29. Conclusions The EXTEND data suggest that oral eltrombopag was well tolerated and safe Eltrombopag up to 75 mg/day increased and sustained platelet counts >50,000/μL in the majority of patients Eltrombopag reduced the incidence and severity of bleeding

  30. HCV Phase II Study 250 Placebo 200 30 mg 50 mg 75 mg 150 Median Platelet Count 100 50 INITIATION MAINTENANCE 0 0 14 28 42 56 70 84 98 112 Study Day McHutchison, NEJM 2007

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