Tailoring caplacizumab administration using ADAMTS13 activity for immune-mediated thrombotic thrombocytopenic purpura.

Caplacizumab, a nanobody targeting the A1 domain of von Willebrand factor (VWF), rapidly inhibits VWF interaction with platelets. This inhibition effectively prevents microthrombus formation and has led to its increasing use as a frontline disease-modifying agent. Clinical trial and postmarketing data suggest that caplacizumab administration guided by ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 motif, member 13) recovery may be as effective and possibly safer than the dosing recommended by the manufacturer. Accordingly, this before-after cohort study sought to compare historical cases of immune thrombotic thrombocytopenic purpura (iTTP) (20 episodes) managed without caplacizumab with cases of iTTP (20 episodes) using a tailored approach to caplacizumab administration based on ADAMTS13 activity measured twice weekly during the hospital stay. Caplacizumab was discontinued when the ADAMTS13 activity was ≥20% on 2 consecutive occasions. Caplacizumab-treated patients received 6 doses (range, 2-30), an 81% reduction relative to the number of doses based on the manufacturer's recommendations (35+), leading to cost savings of $6 466 800. Platelet count normalization occurred at 4 days in caplacizumab-treated patients vs 6 days in the non-caplacizumab cohort (