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Efgartigimod Promotes Sustained Platelet Count Response in iTP

December 6, 2022

February 2023

Treatment with efgartigimod (EFG) resulted in platelet count increases as well as high sustained platelet count responses in patients with persistent or chronic immune thrombocytopenia (iTP), according to a study presented at the 64th ASH Annual Meeting and Exposition.

“There is a need for better iTP therapy,” said study author Catherine M. Broome, MD, of Georgetown University in Washington, DC. “While current treatment options for iTP are many, they can be associated with comorbidities, unsatisfactory efficacy and effect duration, and they can have a limited impact on quality-of-life measures.”

Dr. Broome and colleagues sought to test the efficacy and safety of EFG in a phase III, double-blind trial of adult patients. EFG works by competitively inhibiting the neonatal Fc receptor (FcRn), thus preventing recycling of endogenous IgG and reducing IgG blood levels and IgG autoantibody levels.

The team randomized 131 patients in a 2:1 ratio of EFG 10 mg/kg or placebo for 24 weeks. Patients could continue to take their current iTP therapies at their same initial dosage, with the exception of romiplostim.

The majority of patients had previously tried multiple therapies for iTP, and they all had long-standing disease duration (mean 10.3 years), a refractory population that tends to be very difficult to treat, Dr. Broome noted.

The study achieved its primary endpoint in terms of sustained platelet count response, defined as a minimum platelet count of 50 × 109/L during at least four of six visits between weeks 19 and 24 without intercurrent events such as rescue therapy at week 12 or later, in 21.8% of patients versus placebo (5%). Secondary endpoints included extent of disease control in chronic iTP, proportion of all patients with sustained platelet count response, incidence of bleeding events, and durable sustained platelet response in all patients.

Dr. Broome noted that 38.4% of patients treated with EFG reached a platelet count of 30 × 109 platelets at week one, the threshold at which patients are not expected to experience significant spontaneous bleeding events. This compared to 11.1% of placebo-treated patients.

The study was designed such that patients received weekly EFG dosing for weeks one to four, after which dosing was switched to every other week in patients who achieved a pre-specified platelet level. Notably, 90% of the patients who switched to every other week dosing because of sufficient platelet counts were able to maintain their platelet levels. Thus, Dr. Broome suggested clinicians may have some flexibility in dosing.

“In whatever subgroup we analyzed, [EFG] showed a benefit over placebo,” Dr. Broome said.

This applied to criteria such as history of splenectomy, baseline treatment, time since diagnosis, prior treatment history (including rituximab or thrombopoietin receptor agonist treatment), and age.

Most adverse events (AEs) experienced by patients were mild to moderate, and all were consistent with previous studies of EFG.

“One might wonder about an increased risk of infection if we are decreasing antibody levels, but this was not noted in this trial,” Dr. Broome said.

“The benefits of targeting the neonatal receptor and lowering total IgG levels were demonstrated by clinically and statistically significant improvements in platelet counts compared with placebo,” she said. “It’s a great drug to look at for patients who have not responded to a steroid, to another immunosuppressant, or to thrombopoietin receptor agonists.”

However, she noted, data from this specific trial don’t clarify whether it could also make sense to use EFG as an initial agent in some patients. The research team plans to continue to evaluate the efficacy and safety of EFG during the ongoing open-label extension trial, in which more than 90% of patients are continuing to participate.

Any conflicts of interest declared by the authors can be found in the original abstract.

Reference

Broome CM, McDonald V, Miyakawa Y, et al. Efficacy and safety of intravenous efgartigimod in adults with primary immune thrombocytopenia: results of a phase 3, multicenter, double-blinded, placebo-controlled, randomized clinical trial (ADVANCE IV). Abstract #3. Presented at the 2022 American Society of Hematology Annual Meeting and Exposition; December 11, 2022; New Orleans, Louisiana.

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