Tests of drugs to slow or even stop the cognitive decline that is the hallmark of Alzheimer's have so far been disappointing. A leading theory of why this is holds that the drugs are being given too late. By the time Alzheimer's patients show signs of dementia, the brain damage may be so extensive that the drugs are of little use, according to this theory.
Drug developers want to try giving their drugs to patients earlier, but they've been stymied by the U.S. Food and Drug Administration's requirement that drug trials show improvement in cognition and activities of daily living. And how can one show improvement when the decline has not yet happened?
In recognition of this conundrum, the FDA has proposed in an article in the New England Journal of Medicine, to loosen its current requirements for drug trials. Instead of needing to show improvement in cognition and functions of daily living after taking the experimental drug, the trials could instead measure how well the patient was able to maintain his or her level of mental functioning from the start of the trial to the end of the study, along with tracking a physical Alzheimer's sign (a biomarker), such as beta-amyloid plaque development in the brain.
Since beta-amyloid plaques in the brain can only be spotted in a living person using brain PET imaging, study subjects would presumably need such imaging tests both before being enrolled in a study and possibly at various points during the study.
Eli Lilly's PET tracer florbetapir, known by the brand name Amyvid, was FDA approved as an Alzheimer's imaging test agent last spring, but it is still fairly rare in outpatient imaging centers and community hospitals for some very good reasons. It is expensive — a single dose can cost $1,600, and that is before the cost of the PET imaging procedure and the radiologists' reads are added on. No government or private payor covers the test. In addition, florbetapir has a short half life and will expire if not given to the patient within a fairly small time window. Finally, the resulting PET images must be read by specially-trained radiologists, which are few and far between.
RadNet was one of the first outpatient imaging chains to begin offering the test. Last July, it launched its "Shine a New Light on Dementia" program at 10 locations, partly in order to prepare for what Judith Rose, M.D., the company's director of PET/CT and nuclear medicine, p redicted might be the first wave of demand for the test from researchers seeking to design more selective clinical trials for the next generation of treatment options.
With this move by the FDA, Dr. Rose's prediction may indeed be coming true — at least according to Dr. P. Murali Doraiswamy, M.D., professor of psychiatry at Duke University School of Medicine, who is known as a national expert on Alzheimer's.
“There is more motivation now to invest in the field,” he told the New York Times.
In another positive sign, Siemens PETNet -- the largest distributor of Amyvid -- also announced that it would expand production and make the tracer available in eight additional U.S. cities. They are: Denver; Raleigh, N.C.; Boston; Minneapolis; Hackensack, N.J.; Los Angeles, Fort Lauderdale, Fla; and Cleveland. This brings the total number of cities where PETNet distributes Amyvid to 17.