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Treatment of acquired TTP with caplacizumab
Which laboratory parameters are affected by caplacizumab and how?
VWF activity and antigen are increased, while FVIII:C level is decreased.
FVIII:C, VWF activity and antigen levels are increased.
FVIII:C, VWF activity and antigen levels are decreased.
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Caplacizumab (Cablivi®, Sanofi-Aventis) is a humanised, bivalent nanobody targeting the A1 domain of von Willebrand factor (VWF) used for the treatment of acquired thrombotic thrombocytopenic purpura (aTTP) in combination with plasmapheresis and immunosuppression (1, 2). aTTP is a rare, life-threatening autoimmune blood clotting disorder caused by inhibitory autoantibodies to the von Willebrand factor (VWF)-cleaving protease ADAMTS-13. Decreased ADAMTS-13 activity leads to accumulation of extremely large (UL) VWF multimers, which bind to platelets and induce microthrombus formation, cause tissue ischaemia and organ dysfunction, and potentially lead to overt severe thromboembolic complications such as stroke and myocardial infarction, and arterial and venous thrombosis (3, 4, 5, 6).
The pharmacological action of caplacizumab results in a reduction of VWF activity (ristocetin-induced platelet aggregation (RIPA) or ristocetin cofactor (VWF:RCo)) and VWF antigen levels (VWF AG). Since coagulation factor VIII (FVIII) is bound in a complex to VWF in the blood, a reduction in the coagulation factor VIII concentration (FVIII:C) in plasma occurs in parallel (7). Patients under stable therapy with a daily subcutaneous dose of 10 mg caplacizumab have a VWF AG level reduced by approx. 50% with a similarly strong reduction in FVIII:C (7). The reduction of the VWF activity is markedly greater than that of the antigen level: VWF:RCo falls below 20% and RIPA below 10% of the norm (7). However, the reduced VWF and FVIII:C concentrations and activities are only transient and usually return to baseline levels seven days after treatment has been discontinued.
The most common side effects in patients treated with caplacizumab include bleeding events in various areas of the body (nose, gums, etc.) (7, 8, 9, 10). Due to this increased risk of bleeding in patients receiving caplacizumab therapy, concomitant treatment with platelet aggregation inhibitors, unfractionated or low molecular weight heparin, or oral anticoagulants requires a specific risk-benefit assessment and close clinical monitoring.
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 Peyvandi F, et al. (2021): Caplacizumab prevents refractoriness and mortality in acquired thrombotic thrombocytopenic purpura: integrated analysis. Blood adv; 5 (8): 2137–41.
 Mazepa MA, et al. (2019): How targeted therapy disrupts the treatment paradigm for acquired TTP: the risks, benefits, and unknowns. Blood; 134 (5): 415–20.