FDA Adds Boxed Warning to Adzynma After Reports of Serious Antibody Reactions

Adzynma Boxed Warning

Adzynma Boxed Warning: The U.S. Food and Drug Administration updated Adzynma labeling on September 23, 2026, after postmarketing reports linked the congenital thrombotic thrombocytopenic purpura (cTTP) treatment to neutralizing antibodies against ADAMTS13. In serious cases, those antibodies can reduce or prevent the treatment from working and have been associated with death.

Summary: The FDA added a Boxed Warning and updated prescribing information. The agency says patients on Adzynma should not stop treatment without talking to a health care provider first. See FDA’s September 2026 action and our editorial standards.

By Healthy Golden Gems Health Desk · Published September 25, 2026

Adzynma Boxed Warning: why the FDA acted

Adzynma is a recombinant form of the ADAMTS13 enzyme. The FDA approved it in November 2023 for routine prevention and on-demand treatment of cTTP in adults and children. The FDA describes it as the only FDA-approved recombinant ADAMTS13 therapy for cTTP.

Congenital TTP is a rare inherited blood disorder associated with severe deficiency of ADAMTS13, an enzyme involved in controlling abnormal blood clotting. The NIH National Heart, Lung, and Blood Institute explains that ADAMTS13 helps regulate clot formation and that recombinant ADAMTS13 can replace deficient enzyme in people with congenital TTP.

The newly added warning concerns a different problem. Some patients treated with Adzynma can develop antibodies that neutralize ADAMTS13. When these antibodies interfere with the enzyme, the medicine may provide less benefit or stop working effectively. The FDA’s updated prescribing information states that serious outcomes, including death, have been reported in the postmarketing setting.

FDA Identified the Safety Signal Through Postmarketing Reports

The safety issue emerged after Adzynma was already on the market. The FDA said its safety monitoring identified reports of neutralizing antibodies to ADAMTS13 in patients receiving the medicine.

The FDA previously issued a safety communication in November 2025 after receiving reports involving neutralizing antibodies, including one death. At that time, the agency said it was investigating the risk and evaluating whether additional regulatory action was necessary.

The September 23, 2026 approval letter confirms that the agency approved the addition of a Boxed Warning and updates to the Warnings and Precautions, Immunogenicity and Patient Information sections of the U.S. prescribing information.

What Happened in the Reported Fatal Case?

The FDA’s earlier safety communication described a pediatric patient with cTTP who developed progressively worsening neurologic symptoms. Neutralizing antibodies to ADAMTS13 were identified approximately 10 months after the patient began prophylactic treatment with Adzynma.

The patient had previously experienced severe allergic reactions to fresh frozen plasma. The FDA said the reported death appeared to be related to Adzynma, while also noting an important limitation involving the available antibody testing. Current assays cannot distinguish neutralizing antibodies directed against recombinant ADAMTS13 from neutralizing antibodies directed against the body’s own ADAMTS13.

The FDA’s September 2026 communication now identifies the serious antibody risk in the drug’s Boxed Warning.

Adzynma Boxed Warning: what it means

A Boxed Warning is the most prominent safety warning that the FDA can require on prescription drug labeling. It is used for serious or potentially life-threatening risks.

For Adzynma, the new warning focuses specifically on neutralizing antibodies against ADAMTS13. The updated prescribing information states that these antibodies may lead to a decreased or absent response to recombinant or plasma-derived ADAMTS13.

The warning does not mean that every person receiving Adzynma will develop neutralizing antibodies. Rather, it communicates a documented safety risk that requires attention and monitoring.

The FDA also says that neutralizing antibodies were not reported in the cTTP clinical trials. The newly recognized safety information came from postmarketing experience after the medicine had been approved and used outside the original clinical-trial setting.

What Should Patients Taking Adzynma Know?

The FDA’s guidance is clear that patients currently receiving Adzynma should not stop treatment on their own.

Instead, patients should discuss concerns with their health care provider. The FDA recommends testing before and during treatment to monitor for inhibitors and determine whether Adzynma continues to work as intended.

The agency says patients should contact their health care provider promptly and stop treatment if they experience certain potentially serious reactions, including rash or hives, itching, throat tightness, chest pain or tightness, difficulty breathing, lightheadedness, dizziness, nausea or fainting.

This article is educational reporting—not personal medical advice. Read our medical disclaimer.

Why Monitoring Matters

The FDA’s updated labeling calls for close monitoring of ADAMTS13 activity and the development of neutralizing antibodies before treatment begins and periodically during treatment.

The central concern is whether neutralizing antibodies interfere with ADAMTS13 activity enough to reduce the treatment’s effectiveness. The updated FDA labeling therefore places laboratory monitoring alongside the medication’s existing treatment role.

Adzynma Remains an FDA-Approved Treatment for cTTP

The new warning does not represent a withdrawal of Adzynma from the U.S. market. The FDA’s current product information continues to list Adzynma as approved for prophylactic or on-demand enzyme replacement therapy in adult and pediatric patients with congenital TTP.

The regulatory action instead changes the safety information that accompanies the medicine. The FDA specifically tells current Adzynma patients to consult their health care provider before making changes to treatment.

What Is Still Uncertain?

The available information does not establish that every patient treated with Adzynma faces the same level of risk. The FDA also notes that there are no data on immunogenicity in patients who had never previously been exposed to plasma-based products.

Because cTTP is rare, evidence about the condition and its treatments is necessarily based on relatively small patient populations.

The new FDA warning should be understood as a regulatory response to identified postmarketing safety information, rather than as evidence that the medicine is unsafe for every patient.

What Happens Next?

The updated Adzynma labeling is now part of the FDA’s regulatory safety information for the medicine. The agency will continue receiving adverse-event reports through its safety monitoring system. Patients and health care professionals can report suspected adverse events to FDA MedWatch.

For patients receiving Adzynma, the immediate practical issue is communication with the treating health care team and appropriate laboratory monitoring, rather than stopping treatment without medical guidance.

What This FDA Action Means

The September 2026 action adds an important safety warning to the prescribing information for Adzynma after the FDA identified serious postmarketing reports involving neutralizing antibodies to ADAMTS13.

The medicine remains an FDA-approved treatment for congenital TTP, but the updated labeling emphasizes the importance of monitoring for antibodies and ADAMTS13 activity.

For patients and caregivers, the FDA’s central message is straightforward: do not discontinue Adzynma without first discussing the treatment with the prescribing health care professional.

FAQ

Why did the FDA add a Boxed Warning to Adzynma? The FDA added the warning after postmarketing reports of neutralizing antibodies to ADAMTS13. These antibodies can reduce or prevent the response to ADAMTS13 treatment, and serious outcomes, including death, have been reported.

Does the FDA recall Adzynma? The September 23, 2026 FDA action is a labeling change that adds a Boxed Warning. The FDA’s announcement does not describe a product recall.

Should patients stop taking Adzynma? The FDA says patients currently receiving Adzynma should not stop treatment without first consulting their health care provider.

What is congenital thrombotic thrombocytopenic purpura? Congenital TTP is a rare inherited blood disorder associated with severe deficiency of ADAMTS13. The enzyme plays an important role in regulating blood clotting.

How are patients monitored for the newly identified risk? The FDA recommends monitoring ADAMTS13 activity and testing for the development of neutralizing antibodies before treatment and periodically during treatment.

Has the FDA previously warned about Adzynma? Yes. In November 2025, the FDA issued a safety communication after receiving postmarketing reports of neutralizing antibodies, including one death, and said it was evaluating whether additional regulatory action was needed.

Published: September 25, 2026