Alternate-Day Dosing of Caplacizumab for Immune-Mediated Thrombotic Thrombocytopenic Purpura

Background: The anti-VWF nanobody caplacizumab directly prevents the fatal microthrombi formation in immune-mediated thrombotic thrombocytopenic purpura, thereby adding a new therapeutic principle to the treatment of this autoimmune disorder. However, real-world treatment modalities beyond clinical trials remain heterogeneous.

Methods: Here, we describe the risks and benefits of an alternate-day dosing regimen for caplacizumab, by thoroughly analyzing the timing and outcome of this treatment approach in a retrospective cohort of 25 iTTP patients treated with caplacizumab in Austria and Germany between 2018 and 2021.

Results: Alternate-day dosing of caplacizumab appeared feasible and led to persisting normal platelet counts in the majority of patients, who were converted after a median time of 17 days daily treatment. Four patients experienced iTTP exacerbations or relapses that led to the resumption of daily caplacizumab application and/or other therapies. VWF activity was repeatedly measured in 17 out of 25 patients and documented sufficient suppression by caplacizumab after 24 and 48 hours, in line with published pharmacokinetics.

Conclusion: Extension of caplacizumab injection intervals from daily to alternate-day dosing may be safely considered in selected patients after 30 days of daily treatment. Earlier modifications may be considered in low-risk patients, but require close monitoring for clinical and laboratory features of thrombotic microangiopathy.