As hematologists debated the role of the anti–von Willebrand factor agent caplacizumab for acquired thrombotic thrombocytopenic purpura (TTP), an investigator on the phase 3 trial that led to its approval had a message.
,” said hematologist Spero Cataland, MD, of the department of internal medicine at Ohio State University in Columbus.
If cost is going to be a factor, and it “has to be in our world these days, it’s more of a discussion,” he said during his presentation at the 2020 Update in Nonneoplastic Hematology virtual conference.
The HERCULES trial Dr. Cataland helped conduct found a median time to platelet count normalization of 2.69 days when caplacizumab was started during plasma exchange versus 2.88 days for placebo; 12% of patients had a TTP recurrence while they continued caplacizumab for 30 days past their last exchange and were followed for an additional 28 days versus 38% randomized to placebo. Caplacizumab subjects needed an average of 5.8 days of plasma exchange versus 9.4 days in the placebo arm (N Engl J Med. 2019 Jan 24;380(4):335-46).
Based on the results, the Food and Drug Administration approved the agent for acquired TTP in combination with plasma exchange and immunosuppressives in Feb. 2019 for 30 days beyond the last plasma exchange, with up to 28 additional days if ADAMTS13 activity remains suppressed. Labeling notes a risk of severe bleeding.
“The data on refractory disease and mortality aren’t quite there yet, but there’s a suggestion [caplacizumab] might impact that as well,” Dr. Cataland said. In its recent TTP guidelines, the International Society on Thrombosis and Haemostasis gave the agent only a conditional recommendation, in part because it’s backed up only by HERCULES and a phase 2 trial.
Also, the group noted that in the phase 2 study caplacizumab patients had a clinically and statistically significant increase in the number of relapses at 12 months: 31% versus 8% placebo. “Caplacizumab may leave patients prone to experience a later recurrence owing to the unresolved ADAMTS13 deficiency and inhibitors,” Dr. Cataland said.
“We do see some early recurrence” when caplacizumab is stopped, suggesting that when the agent’s “protective effect is removed, the risk is still there,” said Dr. Cataland, who was also an author on the ISTH guidelines, as well as the phase 2 trial.
It raises the question of how long patients should be kept on caplacizumab. There are few data on the issue, “but the consensus has been to stop caplacizumab when two consecutive ADAMTS13 measurements show 20% or greater activity,” or perhaps with one reading above 20% in a patient trending in the right direction. “With a bleeding complication, you might stop it sooner,” he said.
Dr. Cataland anticipates TTP management will eventually move away from plasma exchange to more directed therapies, including caplacizumab and perhaps recombinant ADAMTS13, which is in development.
There have been a few reports of TTP patients who refuse plasma exchange on religious grounds being successfully treated with caplacizumab. Dr. Cataland also noted a patient of his with relapsing TTP who didn’t want to be admitted yet again for plasma exchange and steroids at the start of a new episode.
“We managed her with caplacizumab and rituximab, and in a couple weeks she had recovered her ADAMTS13 activity and was able to stop the caplacizumab.” She was a motivated, knowledgeable person, “someone I trusted, so I was comfortable with the approach. I think that may be where we are headed in the future, hopefully,” he said.
Dr. Cataland disclosed research funding and consulting fees from Alexion, caplacizumab’s maker, Sanofi Genzyme, and Takeda,. The conference was sponsored by MedscapeLive. MedscapeLive and this news organization are owned by the same parent company.