FDA adds boxed warning to Adzynma for antibodies that can block treatment

FDA has added a boxed warning to Adzynma (recombinant ADAMTS13) after postmarketing reports of neutralizing antibodies that can prevent the enzyme replacement therapy from working. Serious outcomes have included the death of a 7-year-old child. Adzynma is approved for prevention and on-demand treatment of congenital thrombotic thrombocytopenic purpura (cTTP) in adults and children. It replaces ADAMTS13, an enzyme that helps prevent abnormal blood clotting and is severely deficient in people with cTTP.

The practice change is to assess both ADAMTS13 activity and neutralizing antibodies before starting Adzynma and periodically throughout treatment, including in patients previously treated with plasma products. If expected activity levels are not reached, or a TTP exacerbation occurs despite appropriate dosing, the revised prescribing information calls for an assay measuring neutralizing antibody concentrations. These antibodies may also reduce response to plasma-derived ADAMTS13.

The fatal case involved a child whose neurologic symptoms progressively worsened. Neutralizing antibodies were identified about ten months after prophylactic treatment began. Neutralizing antibodies were not reported in the cTTP trials, and the frequency of this postmarketing risk cannot be reliably estimated.

Patients should be told not to stop Adzynma without consulting their treating clinician. If they develop possible hypersensitivity symptoms, such as hives, throat or chest tightness, or difficulty breathing, they should stop treatment and contact their HCP immediately.

Source: FDA. (2026 Sep 23) FDA Takes Action on New Boxed Warning for Adzynma Enzyme Replacement Therapy for Congenital Thrombotic Thrombocytopenic Purpura (cTTP)