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  1. Safety & Availability (Biologics)

FDA Takes Action on New Boxed Warning for Adzynma Enzyme Replacement Therapy for Congenital Thrombotic Thrombocytopenic Purpura (cTTP)

Date: 09/23/2026

Summary of the Issue

The U.S. Food and Drug Administration is alerting patients, caregivers, and health care providers that Adzynma, a recombinant ADAMTS13 enzyme replacement therapy approved for congenital thrombotic thrombocytopenic purpura (cTTP), has been associated with the development of neutralizing antibodies (blocking antibodies) that can prevent the drug from working. In serious cases, this has resulted in death, including of a 7-year-old child.
In response, the FDA has directed the manufacturer, Takeda Pharmaceuticals, to add a Boxed Warning, the most serious type of warning the FDA can require on a drug label, to Adzynma's prescribing information. This Boxed Warning alerts health care providers and patients to the risk of developing blocking antibodies and the serious consequences, including death, that may follow.

Patients currently receiving Adzynma should not stop treatment without first consulting their health care provider. Health care providers should monitor all patients with regular laboratory testing to detect blocking antibodies as early as possible.

Background and Key Safety Information  

Adzynma is a lab-manufactured enzyme replacement therapy, which the FDA approved on Nov. 9, 2023, for both routine prevention and on-demand treatment of cTTP in adults and pediatric patients. Adzynma is the only FDA-approved recombinant ADAMTS13 therapy for cTTP, a rare, inherited blood disorder caused by a severe deficiency of the ADAMTS13 enzyme, which is essential for preventing abnormal blood clotting. The drug contains two slightly modified forms of the ADAMTS13 protein, one of which matches the natural human sequence.

A safety signal associated with Adzynma was identified through FDA's Adverse Event Reporting System (FAERS), a postmarketing surveillance database through which health care providers, manufacturers, and patients submit reports of adverse events and medication errors, enabling the agency to continuously monitor the real-world safety profile of approved products and take regulatory action when emerging risks are identified. 

The reported fatal case involved a 7-year-old child who developed neurologic symptoms that progressively worsened. Neutralizing antibodies to ADAMTS13 were identified around 10 months after starting prophylactic treatment with Adzynma. The patient had a prior history of severe allergic reactions to fresh frozen plasma. At that time, the FDA issued a Safety Communication to alert patients and health-care providers.

The revised labeling includes specific safety information and monitoring recommendations:

  • Do not stop taking Adzynma without first talking to your health care provider.
  • Contact your healthcare provider right away and stop treatment if you get a rash or hives, itching, tightness of the throat, chest pain or tightness, difficulty breathing, lightheadedness, dizziness, nausea, or fainting. Tell your healthcare provider about any side effect that bothers you or does not go away.
  • For your safety, get tested before and during treatment. Ask your healthcare provider about getting a baseline blood test before you start treatment and regular follow-up blood tests while you are on treatment. These tests check whether inhibitors have developed and whether Adzynma is still working as it should.
  • If you have questions or concerns, contact your health care provider.
  • Report side effects to FDA MedWatch at 1-800-FDA-1088 or at www.fda.gov/medwatch.
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