FDA Approves Drug to Image Tau Tangles in Alzheimer’s Disease

In May the Food and Drug Administration (FDA) approved the first drug for use in imaging abnormal tau protein, which is thought to be a primary marker of Alzheimer’s disease.

Flortaucipir F18 (Tauvid) is an intravenous radioactive agent for use in positron emission tomography imaging of the brain to estimate the density and distribution of aggregated tau neurofibrillary tangles (NFTs) in adults with cognitive impairment. These tangles consist of abnormal tau proteins inside the neurons of the brain. The drug works by binding to sites in the brain where abnormal tau proteins grow.

“This approval will provide health care professionals with a new type of brain scan to use in patients being evaluated for Alzheimer’s disease,” said Charles Ganley, M.D., director of the Office of Specialty Medicine in the FDA’s Center for Drug Evaluation and Research, in a press release.

Gil Rabinovici, M.D., the Edward Fein & Pearl Landrith Distinguished Professor in the departments of Neurology, Radiology, and Biomedical Imaging at the University of California, San Francisco (UCSF), said that diagnostic scans with flortaucipir F18 will be useful for more than detecting where tangles reside in the brain.

“It can help us predict where the brain may atrophy in the coming years, which can help us predict the course of the disease,” Rabinovici told Psychiatric News. “It will also be useful for helping patients and their families to understand [the diagnosis] because we can explain to them where the tangles are happening.”

The FDA’s approval was based on two studies involving brain scans that used flortaucipir F18. In the first study, five evaluators evaluated the scans of 156 terminally ill patients and interpreted the scans as positive or negative for NFTs. Sixty-four of the patients died within nine months of their scans. Researchers compared the evaluators’ readings of the deceased patients’ scans with postmortem assessments of the density and distribution of NFTs in the same brains by independent pathologists. The study showed that the five evaluators had a high probability of correctly noting tau pathology in patients who had it and an average-to-high probability of correctly noting no tau pathology in patients who did not have it.

The second study included the same patients as the first study along with 18 patients with terminal illness and 159 patients with cognitive impairment who were being evaluated for Alzheimer’s disease. In this study, five new evaluators reviewed each other’s readings of the scans, and the researchers rated how well the evaluators agreed with one another’s assessments. Perfect agreement was scored as 1, and no agreement was scored as 0. Agreement was 0.87 across all 241 patients.

The most common side effects were headache, pain at the injection site, and increased blood pressure, with all side effects occurring in less than 1.5% of the patients.

Flortaucipir F18 was developed by Avid Radiopharmaceuticals Inc., a subsidiary of Eli Lilly and Co. In a statement, Lilly noted that availability of flortaucipir F18 will be limited initially and will expand in response to demand and coverage by insurers.

“Access is going to be very limited [at first] because right now these scans are not reimbursed by insurance and they are very expensive,” Rabinovici said. ■