No, you are incorrect. It might cost billions to develop them from scratch, but those are already sunk costs. Additional testing and trials do not cost nearly so much. In fact, while they may cost more in some circumstances, the average is only $19 million [0]
That means that even testing the half dozen or so anticonvulsants known to have neuroprotective benefits it would cost in the range of $100 million.
But for the sake of argument, let's grant your premise anyway and see where it leads. Let's say it costs billions, even $20 billion to do the trials. The annual cost of Alzheimers may top $250 billion. So the cost/benefit analysis still works out either way. In fact, in that context the potential savings make the difference between $100 million and $20 billion pretty negligible if the drugs could normalize even a few years for the average patient that would otherwise be plagued with dementia.
That means that even testing the half dozen or so anticonvulsants known to have neuroprotective benefits it would cost in the range of $100 million.
But for the sake of argument, let's grant your premise anyway and see where it leads. Let's say it costs billions, even $20 billion to do the trials. The annual cost of Alzheimers may top $250 billion. So the cost/benefit analysis still works out either way. In fact, in that context the potential savings make the difference between $100 million and $20 billion pretty negligible if the drugs could normalize even a few years for the average patient that would otherwise be plagued with dementia.
[0] https://www.outsourcing-pharma.com/Article/2018/09/26/Clinic...