The FDA approved its first radioactive diagnostic dye designed to map out the characteristic tau protein tangles found in the brains of people with Alzheimer’s disease—information that previously required an autopsy.
The Tauvid injection, developed by Eli Lilly’s Avid Radiopharmaceuticals subsidiary, contains a molecule that binds to sites in the brain associated with tau protein misfolding, tagging them with a radioisotope visible under a PET scan.
This can help clinicians estimate the density and scope of the neurofibrillary tangles that form within neurons and disrupt signaling, and provides a way to measure tau pathology—one of the two key methods, along with amyloid pathology, for evaluating the brains of patients for Alzheimer’s.
“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, director of the FDA’s Office of Specialty Medicine in its drug evaluation branch.
“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,” Ganley added.
The FDA previously approved Lilly and Avid’s Amyvid radioactive agent in 2012 for similarly highlighting amyloid plaque under a PET scan.
"The fight against [Alzheimer’s disease] requires precise and reliable assessments of the two key pathologies of the disease because clinical assessments alone are limited in their ability to accurately diagnose patients," said Mark Mintun, vice president of Lilly's pain and neurodegeneration R&D, who described the availability of both agents as way to provide a more comprehensive evaluation of patients.
In clinical studies of terminally ill patients, the outcome of Tauvid brain scans were compared to post-mortem analyses of donated brain tissue. Evaluations of the images had high probabilities of correctly spotting tau pathology, though it was less accurate in completely ruling it out.
According to the FDA, Tauvid was assessed in patients with generally severe stages of dementia and its performance may be lower in earlier stages of cognitive decline.
Lilly said Tauvid’s initial availability will be limited, though the drugmaker plans to expand based on commercial demand and payor reimbursement.