The Use of Global Assays to Monitor Emicizumab Prophylactic Therapy in Patients with Hemophilia A with Inhibitors Mid-Atlantic Region III HTCs Annual Meeting Alexandria, VA March 15, 2019 Janice G. Kuhn, RN, MPH Virginia Commonwealth University

Disclosures None

Donald F. Brophy, Pharm.D., M.Sc., FCCP, BCPS Nancy L. and Ronald H. McFarlane Professor of Pharmacy Chairman, Department of Pharmacotherapy & Outcomes Science Professor of Medicine Virginia Commonwealth University School of Pharmacy Erika Martin, MT Research Professor DOI: 10.1111/hae.13689

Emicizumab Humanized bi-specific antibody directed against activated factor IX (FIXa) and factor X (FX). Functions as a bridge between FIXa and FX in the tenase complex, thereby mimicking the co-factor function of activated factor VIII.

Emicizumab: Problems with laboratory monitoring Emicizumab therapy interferes with any coagulation test that measures the intrinsic coagulation pathway, including: Activated clotting time Bethesda FVIII inhibitor titer assay Single factor assays Traditional coagulation tests to quantify response to therapy are unreliable. Additionally, significant inter-patient variance in emicizumab metabolism and/or the potential for antibody development to the drug underscore the need for accurate laboratory monitoring

Can we use global assays to measure response to Emicizumab: a Case Study

Thromboelastography (TEG) What does it do? Demonstrates the contributions and interactions of hemostatic components during clotting, especially the role of the platelet Measures the hemostatic potential of the blood at a given point in time. Is not a “clotting assay” which depends upon comparison to a “standard” dilutional response to the presence of factor between a control and the sample

TEG® Data Related to Pathways

TEG® R and K Time R–time The “waiting period” until a the fibrin formation K–time The time it takes to achieve a certain level of clot strength (amplitude 20 mm)

What influences R and K time? Factor deficiency Anti-coagulation Residual heparin Severe hypofibrinogenemia Severe thrombocytopenia R and K time  Hypercoagulable state

TEG® Pattern Recognition

Caveats of interpretation of TEG® In the clinical setting, TEGs are often used to monitor hypo or hypercoagulable states Cardiac bypass surgery Echo High-risk OB Trauma Therefore, target values may vary.

Thrombin Generation Assay Thrombin burst: the penultimate event in hemostasis Thrombosis time thrombin Normal Bleeding Tripodi A. The long-awaited whole-blood thrombin generation test. Clin Chem 2012; 58:

Thrombin Generation Assay What are we measuring? Clot forms Clotting Time Calibrated Automated Thrombogram (CAT) system measurement parameters: Lag Time- Time to initial thrombin generation Peak- Maximum amount of thrombin generated Time to peak-Time to generate maximum amount of thrombin ETP- ---Area under the curve; overall potential to generate thrombin VI- Velocity index/ rate of thrombin formation

Thrombin Generation Assay Factor VIII or Factor IX Deficiency Normal Thrombin Generation Emicizumab Action on FVIII Deficiency Emicizumab

Patient 1 Severe Factor VIII Deficiency with Inhibitor Titer of 1.9 BU Prior to emicizumab: ABR: 12-15 bleeds/year On-demand therapy: rFVIII 100U/kg every 12hr, typically for 48hr to treat bleeds Surgical prophylaxis: rFVIIa Received emicizumab 3 mg/kg subcutaneously initially, followed by 1.5 mg/kg subcutaneously 1 month later

Patient 1: TEG results TEG Normal Range: R-time: 3-8 min k-time: 1-3 min Angle: 54-77 degrees MA: 50-70 mm

TEG results pre/post in comparison to mild Factor VIII Deficiency and control

Patient 1: TGA Results

TGA results TGA Normal Range: Lag-time: 0.5-5 min ETP: 1500-3000 nM/min Thrombin Peak: 300-550 nM

Patient 2 Severe Factor VIII Deficiency with Inhibitor of 7.1 BU Prior to emicizumab: ABR: 4 bleeds/year On-demand therapy: FEIBA 75 mg/kg every 12hr Received emicizumab 3 mg/kg subcutaneously initially, followed by 1.5 mg/kg subcutaneously 1 month later

Patient 2: TEG results

Patient 2: TGA TGA Normal Range: Lag-time: 0.5-5 min ETP: 1500-3000 nM/min Thrombin Peak: 300-550 nM

Conclusions Global coagulation assays successfully monitored the pharmacodynamic response to emicizumab. Normalization of TEG viscoelastic parameters and marked improvements in thrombin generation at 1 and 2 months post‐dose, compared to baseline, consistent with a mild HA phenotype was observed. Clinicians should be aware of the potential pitfalls with using routine coagulation monitoring for emicizumab and should consider using other global coagulation measures to assess emicizumab activity. Larger studies are needed

Further considerations Can you use TEG or TGA for pre-surgical assessment of bleeding risk? All labs were in a non-bleeding state. Would results change in a bleeding state? Would the TEG predict response to BPA from in-vitro response to spiking studies with TGA? Would TEG give you additional information (would it push the R value too low?) Why is there a difference in lag times between TEG and TGA?