1. Using a tailored approach based on the recovery of ADAMTS13 activity, patients were treated with a median of 6 caplacizumab doses.

  2. Compared to the historical cohort, caplacizumab-treated patients showed faster normalization of platelet counts and ADAMTS13 activity.

Neuropsychiatric sequala are increasingly recognized as major long-term complications of immune thrombotic thrombocytopenic purpura (iTTP). Caplacizumab, a nanobody targeting the A1 domain of von Willebrand Factor (VWF), rapidly inhibits VWF interaction with platelets. This inhibition effectively prevents microthrombi formation and has led to its increasing use as a frontline disease-modifying agent. Clinical trial and post-marketing data suggest that caplacizumab administration guided by ADAMTS13 recovery may be as effective and possibly safer compared to dosing recommended by the manufacturer. Accordingly, this before-after cohort study sought to compare historical cases of iTTP (20 episodes) managed without caplacizumab to 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 two 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 versus 6 days in the non-caplacizumab cohort (p=0.2). Rates of exacerbation and relapse were similar between both groups. Ultimately, these findings suggest that tailoring caplacizumab administration based on ADAMTS13 activity recovery leads to a marked reduction in the caplacizumab doses required. Despite this reduction, clinical and laboratory data were similar to those described in clinical trials and post-marketing studies while generating significant cost savings. Given these findings, prospective studies utilizing ADAMTS13 activity to guide individualized caplacizumab therapy are warranted.

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