FDA Okays First Tau Radiotracer to Aid Alzheimer's Diagnosis

Megan Brooks


May 29, 2020

The US Food and Drug Administration (FDA) has approved flortaucipir F18 injection (Tauvid, Avid Radiopharmaceuticals), the first diagnostic tau radiotracer for use with positron-emission tomography (PET) to estimate the density and distribution of aggregated tau neurofibrillary tangles (NFTs) in adults with cognitive impairment who are being evaluated for Alzheimer disease (AD).

"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," Charles Ganley, MD, director, Office of Specialty Medicine, FDA Center for Drug Evaluation and Research, said in an FDA news release.

"The use of diagnostic imaging can help patients and their families plan for the future and make informed choices about their health and well-being, in addition to facilitating appropriate patient management for physicians," Reisa Sperling, MD, director of the Center for Alzheimer Research and Treatment at Brigham and Women's Hospital and Massachusetts General Hospital, Boston, said in a company news release.

"Determining the anatomic distribution and density of tau NFTs in the brain was previously possible only at autopsy. Now we have a way to obtain this important information in patients," said Sperling.

Clinical Trial Results

Following intravenous administration, flortaucipir F18 binds to tau pathology in the brain and can be seen on a PET scan.

The safety and effectiveness of the tau tracer were demonstrated in two clinical studies. In each study, five evaluators, blinded to clinical information, interpreted the flortaucipir F18 PET scan results as positive or negative.

The first study included 156 terminally ill patients who agreed to undergo flortaucipir F18 PET imaging and to donate their brains after death. Of these patients, 64 died within 9 months of undergoing brain scanning. The evaluators' readings of these scans were compared to post mortem readings from independent pathologists blinded to scan results.

Evaluators reading the flortaucipir F18 PET scans 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 FDA said in the release.

According to the company, reader sensitivity ranged from 92% (95% confidence interval [CI], 80% to 97%) to 100% (95% CI, 91% to 100%). Specificity ranged from 52% (95% CI, 34% to 70%) to 92% (95% CI, 75% to 98%).

Initial Limited Availabilty

The second study included the same patients with terminal illness as the first study, plus 18 additional patients who had terminal illness and 159 patients who had cognitive impairment and were being evaluated for AD (the indicated population).

The study gauged how well evaluators' readings of flortaucipir F18 PET scans agreed with each other's assessments of the readings. In this study, reader agreement was 0.87 (perfect agreement was indicated as 1) across all 241 patients.

In a separate subgroup analysis that included the 82 terminally ill patients who were 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.

The FDA notes that the ability of flortaucipir F18 PET scans to detect tau pathology was assessed in patients with generally severe stages of dementia and may be lower in patients with cognitive decline of earlier stages.

The most common adverse reactions among patients who received flortaucipir F18 injection were headache, injection site pain, and an increase in blood pressure. The tau radiotracer is not indicated for use in the evaluation of patients for chronic traumatic encephalopathy.

The FDA granted flortaucipir F18 priority review, in which the FDA aims to take action on an application within 6 months of the time the agency determines that the drug, if approved, would significantly improve the safety or effectiveness of treating, diagnosing, or preventing a serious condition.

The company said the availability of flortaucipir F18 will initially be "limited and will expand in response to commercial demand and payor reimbursement."

AD is among the top 10 leading causes of death in the United States. In 2014, 5 million Americans were living with the disease, according to federal health officials. That number is projected to nearly triple to 14 million by 2060.

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