FDA Panel Narrowly Backs Avacopan Approval

Kerry Dooley Young

May 07, 2021

A panel of federal advisers on May 6 lent support to the ChemoCentryx bid for approval of avacopan for a rare and serious autoimmune condition. But they also flagged concerns about both the evidence supporting claims of a benefit for this experimental drug and its safety.

At a meeting of the Food and Drug Administration's Arthritis Advisory Committee, panelists voted 10-8 on a question of whether the risk-benefit profile of avacopan is adequate to support approval.

ChemoCentryx is seeking approval of avacopan for antineutrophil cytoplasmic autoantibody (ANCA)–associated vasculitis in the subtypes of granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA).

Dr Mara L. Becker

Regardless of their vote on this approval question, the panelists shared an interest in avacopan's potential to reduce glucocorticoid use among some patients with ANCA-associated vasculitis, also called AAV. Mara L. Becker, MD, MSCE, the chair of the FDA's panel, was among the panelists who said they reluctantly voted no.

"It pains me because I really want more steroid-sparing" medicines, said Becker of Duke University, Durham, N.C., who cited a need to gather more data on avacopan.

Margrit Wiesendanger, MD, PhD, of the Icahn School of Medicine at Mount Sinai, New York, who was among the panelists voting yes, spoke of a need for caution if the FDA approves avacopan.

"Judicious use of this new medication will be warranted and perhaps additional guidance could be given to rheumatologists to help them decide for whom this medication is best," she said.

Panelists had spoken earlier of avacopan as a possible alternative medicine for people with AAV who have conditions that make glucocorticoids riskier for them, such as those who have diabetes.

Close Votes on Safety Profile, Efficacy

The panel also voted 10-8 on a question about whether the safety profile of avacopan is adequate to support approval of avacopan for the treatment of adult patients with AAV.

In addition, the panel voted 9-9 on a question about whether efficacy data support approval of avacopan for the treatment of adult patients with AAV.

The FDA considers the recommendations of its advisory panels, but is not bound by them.

The FDA staff clearly expressed the view that ChemoCentryx fell short with the evidence presented for avacopan approval. Shares of San Carlos, Calif.–based ChemoCentryx dropped sharply from a May 3 closing price of $48.82 to a May 4 closing price of $26.63 after the FDA released the staff's review of avacopan.

In a briefing prepared for the meeting, FDA staff detailed concerns about the evidence ChemoCentryx is using to seek approval. While acknowledging a need for new treatments for AAV as a rare condition, FDA staff honed in on what they described flaws in the testing of this experimental medicine, which is a small-molecule antagonist of the receptor of C5a, an end product of the complement cascade that acts as a potent neutrophil chemoattractant and agonist.

The FDA usually requires two phase 3 studies for approval of a new medicine but will do so with a single trial in cases of exceptional need, the agency staff said. But in these cases, the bar rises for the evidence provided from that single trial.

Difficulties in Interpretation of Complex Study Design

In the case of avacopan, though, the data from the key avacopan trial, Study CL010_168, known as ADVOCATE, there were substantial uncertainties around the phase 3 study design and results, raising questions about the adequacy of this single trial to inform the benefit-risk assessment.

In the briefing document, the FDA staff noted that it had "communicated many of the concerns" about ChemoCentryx's research earlier to the company.

"Complexities of the study design, as detailed in the briefing document, raise questions about the interpretability of the data to define a clinically meaningful benefit of avacopan and its role in the management of AAV," the FDA staff wrote.

"We acknowledge that AAV is a rare and serious disease associated with high morbidity and increased mortality. It is also a disease with high unmet need for new therapies. However, FDA wants to ensure that new products have a defined context of use, i.e., how a product would be used, and a favorable benefit-risk assessment for patients," the staff added.

In addition, there were differences in the assessments performed by investigators and the adjudication committee, most frequently related to the attribution of persistent vasculitis, the FDA staff noted.

Statistical analyses of the primary endpoint using investigators' estimates "resulted in more conservative estimates of treatment effect, e.g., statistical significance for superiority would no longer be demonstrated," the FDA staff noted. "While the prespecified analysis used the Adjudicator assessments, the assessment based on the Investigators, experienced in management of vasculitis, may better reflect real-world use."

Imbalances in Use of Glucocorticoids and Maintenance Therapy

Also among the complications in assessing the ADVOCATE trial data were the glucocorticoids taken by patients in the study, the FDA staff said.

In the avacopan arm of the trial, 86% of patients received non–study-supplied glucocorticoids. In addition, more avacopan‐treated patients experienced adverse events and serious adverse events within the hepatobiliary system leading to discontinuation.

Subgroups given different treatments represented another challenge in interpreting ADVOCATE results for the FDA staff.

At week 26, the proportion of patients in disease remission in the avacopan group (72.3%) was noninferior to the prednisone group (70.1%), the FDA staff said in the briefing document.

But at week 52, a disparity was observed between subgroups that had received rituximab and cyclophosphamide (intravenous and oral) induction treatment. The estimated risk difference for disease remission at week 52 was 15.0% (95% CI, 2.2%-27.7%) in the subgroup receiving induction with rituximab and 3.3% (95% CI, –14.8% to 21.4%) in the cyclophosphamide plus maintenance azathioprine subgroup, the agency's staff said.

"Based on the data, there is no evidence of clinically meaningful treatment effect in the cyclophosphamide induction subgroup," the FDA staff wrote. "Further, the treatment comparison in the complementary rituximab induction subgroup may not be considered meaningful because these patients did not receive maintenance therapy, i.e., due to undertreating of patients, the effect observed in the rituximab subgroup may not represent a clinically meaningful treatment effect, compared to standard of care."

Dr Rachel Glaser

Rachel L. Glaser, MD, clinical team leader in FDA's division of rheumatology and transplant medicine, reiterated these concerns to the advisory committee at the May 6 meeting.

"Throughout the development program, FDA advised the applicant that a noninferiority comparison would not be sufficient to show that avacopan can replaced glucocorticoids as it would be difficult to establish whether avacopan is effective or whether an effect was due to the rituximab or cyclophosphamide administered to both treatment arms," she said.

In its briefing for the meeting, ChemoCentryx noted the limits of treatments now available for AAV. It also emphasized the toll of the condition, ranging from skin manifestations to glomerulonephritis to life-threatening pulmonary hemorrhage. If untreated, 80% of patients with GPA or MPA die within 2 years of disease onset, ChemoCentryx said in its briefing materials for the meeting.

The side effects of glucocorticoids were well known to the FDA panelists and the ChemoCentryx presenters. Witnesses at an open public hearing told their own stories of depression, anxiety, and irritability caused by these medicines.

Dr Peter Merkel

During the ChemoCentryx presentation, a presenter for the company, Peter Merkel, MD, MPH, of the University of Pennsylvania, Philadelphia, said avacopan would provide patients with AAV with an alternative allowing them "to go on a much lower glucocorticoids regimen."

A similar view was presented in a February 2021 editorial in the New England Journal of Medicine, titled "Avacopan – Time to Replace Glucocorticoids?" Written by Kenneth J. Warrington, MD, of the Mayo Clinic, Rochester, Minn., the opinion article called the ADVOCATE trial "a milestone in the treatment of ANCA-associated vasculitis; complement inhibition with avacopan has glucocorticoid-sparing effects and results in superior disease control."

Warrington reported no conflicts in connection with his editorial nor payments from ChemoCentryx. He did report grants from other firms such as Eli Lilly.

Julia Lewis, MD, of Vanderbilt University, Nashville, Tenn., was among the more skeptical members of the FDA panel. She was among the "nays" in all three voting questions put to the panel. Still, she said there were signs of "clinically meaningful benefit" in the data presented, but noted that the nonstudy use of glucocorticoids made it difficult to interpret the ADVOCATE results.

Lewis noted that the FDA usually requires two studies for a drug approval, particularly with a compound not yet cleared for any use. While ANCA-associated vasculitis is rare, it would be possible to recruit patients for another trial of avacopan, adding to the results reported already for avacopan from ADVOCATE, she said.

"Were there to be another study, this would certainly be a supportive study and maybe qualify as two studies," she said.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.