WASHINGTON -- Flortaucipir F18 (Tauvid), a radioactive PET tracer, became the first drug approved by the FDA to
image tau pathology in people being evaluated for Alzheimer's disease late Thursday.
PET imaging with flortaucipir F18 can help estimate the density and
distribution of aggregated tau neurofibrillary tangles, a primary marker
of Alzheimer's disease.
"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," said Charles Ganley, MD, director of Office of
Specialty Medicine in the FDA's Center for Drug Evaluation and Research.
The tracer is administered intravenously and binds to sites in the brain associated with tau protein misfolding.
"Determining the anatomic distribution and density of tau
neurofibrillary tangles in the brain was previously possible only at
autopsy," Reisa Sperling, MD, director of the Center for Alzheimer
Research and Treatment at Brigham and Women's Hospital and Massachusetts
General Hospital, said in a
statement. "Now we have a way to obtain this important information in patients."
Two
clinical studies
involving terminally ill older adults assessed flortaucipir's ability
to predict Alzheimer's pathology. In a subset of patients, researchers
compared imaging data to autopsy findings. Flortaucipir F18 PET
predicted B3 level of tau pathology (Braak stage V or VI, indicating tau
deposition in wide areas of the neocortex) with sensitivity ranging
from 92.3% to 100.0% and specificity ranging from 52.0% to 92.0%.
The most common adverse reactions reported in clinical trials were
headache (1.4%), injection site pain (1.2%), and increased blood
pressure (0.8%).
The
tracer's ability to detect tau pathology was assessed in people with
generally severe stages of dementia and may be lower among those in
earlier stages of cognitive decline.
Flortaucipir F18 is not indicated for evaluating patients for chronic
traumatic encephalopathy (CTE), the FDA stated. The tracer recently
showed only a
modest correlation between imaging findings and post-mortem CTE pathology in a former National Football League player.
The agency granted approval to Avid Radiopharmaceuticals, a subsidiary of Eli Lilly. Flortaucipir F18 will have
limited availability at first, which will expand in response to commercial demand and payor reimbursement, the company said.
Medicare coverage will be particularly important, given the
demographics associated with Alzheimer's disease and dementia; it has
been a significant issue for uptake of PET tracers for beta amyloid
plaques such Avid's florbetapir (AmyVid). The Centers for Medicare and
Medicaid Services has insisted on
seeing evidence of clinical benefit before agreeing to full coverage. Despite
studies pointing in that direction, the agency has
not yet altered its policy on amyloid tracers.
