Caplacizumab may hold promise in the treatment of acquired thrombotic thrombocytopenic purpura (TTP), according to trial results published in The New England Journal of Medicine.

The study was a double blind phase 3 trial (HERCULES; Identifier: NCT02553317), in which 145 patients with acquired TTP were randomly assigned to receive either caplacizumab or a placebo control. Time to platelet count normalization was the primary study endpoint, including stoppage of daily plasmapheresis within 5 days of normalization. Multiple TTP-related secondary endpoints were examined.

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The time to reach platelet count normalization was significantly shorter with caplacizumab compared with placebo: With caplacizumab it occurred at a median of 2.69 days (95% CI, 1.89-2.83), but with placebo it occurred at median of 2.88 days (95% CI, 2.68-3.56; P =.01). Caplacizumab was also 1.55 times as likely to be associated with platelet count normalization compared with placebo.

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Throughout the trial, patients experienced TTP recurrence at a lower rate with caplacizumab (12% vs 38%; P <.001). Patients taking caplacizumab also showed a substantially lower rate (12%) of undergoing an incident from a composite endpoint that included thromboembolic events, TTP recurrence while on treatment, and TTP-associated fatality. With placebo this rate was 49% (P <.001).

In the placebo group, there were 3 fatalities during the treatment period. A fatal cerebral ischemia was reported in the caplacizumab group following the treatment period.

There were 3 patients receiving placebo who showed refractory disease; none receiving caplacizumab did. The authors also reported that caplacizumab was associated with shorter hospital stays and a reduced need for plasma exchange. Mucocutaneous bleeding was the most common adverse event for both the caplacizumab (65%) and placebo (48%) groups.

In this study, caplacizumab therapy was associated with faster platelet count normalization in acquired TTP and lower rates of multiple TTP-related risks.


1.     Scully M, Cataland SR, Peyvandi F, et al. Caplacizumab treatment for acquired thrombotic thrombocytopenic purpura [published online January 24, 2019]. N Engl J Med. doi:10.1056/NEJMoa1806311