FDA Approves First Drug to Image Tau Pathology in Patients Being Evaluated for Alzheimer's Disease
Approval Marks Significant Advance Towards a More Definitive Assessment of Alzheimer's Based on Brain Imaging
The FDA recently approved Tauvid (flortaucipir F18) for intravenous injection, the first drug used to help image a distinctive characteristic of Alzheimer's disease in the brain called tau pathology. Tauvid is a radioactive diagnostic agent for adult patients with cognitive impairment who are being evaluated for Alzheimer's disease. Tauvid is indicated for positron emission tomography (PET) imaging of the brain to estimate the density and distribution of aggregated tau neurofibrillary tangles (NFTs), a primary marker of Alzheimer's disease.
"Alzheimer's disease is a devastating condition that affects millions of Americans. This approval will provide health care professionals with a new type of brain scan to use in patients being evaluated for Alzheimer's disease," says Charles Ganley, MD, director of Office of Specialty Medicine in FDA's Center for Drug Evaluation and Research. "While there are FDA-approved imaging drugs for amyloid pathology, this is the first drug approved for imaging tau pathology, one of the two neuropathological hallmarks of Alzheimer's disease, and represents a major advance for patients with cognitive impairment being evaluated for the condition."
Two proteins—tau and amyloid—are recognized as hallmarks of Alzheimer's disease. In patients with Alzheimer's disease, pathological forms of tau proteins develop inside neurons in the brain, creating NFTs. After Tauvid is administered intravenously, it binds to sites in the brain associated with this tau protein misfolding. The brain can then be imaged with a PET scan to help identify the presence of tau pathology.
Alzheimer's disease is a progressive disease that typically begins with mild memory loss. It is one of the top 10 leading causes of death in the United States. According to the US Centers for Disease Control and Prevention, in 2014, there were as many as 5 million Americans living with Alzheimer's disease. This number is projected to nearly triple to 14 million by 2060. Currently, Alzheimer's disease can only be definitively diagnosed by pathologic evaluation of a patient's brain once they have died (postmortem). There are three imaging agents approved for postmortem amyloid pathology with PET scans.
The safety and effectiveness of Tauvid imaging was evaluated in two clinical studies. In each study, five evaluators read and interpreted the Tauvid imaging. The evaluators were blinded to clinical information and interpreted the imaging as positive or negative.
The first study enrolled 156 patients who were terminally ill and agreed to undergo Tauvid imaging and participate in a post-mortem brain donation program. In 64 of the patients who died within nine months of the Tauvid brain scan, evaluators' reading of the Tauvid scan was compared to postmortem readings from independent pathologists who evaluated the density and distribution of NFTs in the same brain. The study showed evaluators reading the Tauvid images had a high probability of correctly evaluating patients with tau pathology and had an average-to-high probability of correctly evaluating patients without tau pathology.
The second study included the same patients with terminal illness as the first study, plus 18 additional patients with terminal illness, and 159 patients with cognitive impairment being evaluated for Alzheimer's disease (the indicated patient population). The study gauged how well Tauvid evaluators' readings agreed with each other's assessments of the readings. Perfect reader agreement would be 1, while no reader agreement would be 0. In this study, reader agreement was 0.87 across all 241 patients. In a separate subgroup analysis that included the 82 terminally ill patients diagnosed after death and the 159 patients with cognitive impairment, reader agreement was 0.90 for the patients in the indicated population and 0.82 in the terminally ill patients.
Tauvid's ability to detect tau pathology was assessed in patients with generally severe stages of dementia and may be lower in patients in earlier stages of cognitive decline than in the patients with terminal illness who were studied.
The most common adverse reactions in patients using Tauvid were headache, injection site pain and increased blood pressure.
Tauvid is not indicated for use in the evaluation of patients for chronic traumatic encephalopathy.
The FDA granted the manufacturer of Tauvid Priority Review, under which the FDA's goal is to take action on an application within six months where the agency determines that the drug, if approved, would significantly improve the safety or effectiveness of treating, diagnosing or preventing a serious condition. The FDA granted approval of Tauvid to Avid Radiopharmaceuticals, Inc.