My experience with amantadine is pretty unremarkable. I started out with 200mg/day not long after dx, then cut back to my current 100mg/day because I thought it was causing foot and ankle swelling. For those who respond to it, I think it is most helpful with balance.
I read somewhere that some of its effects are apparently due to changes in cell and vesicle membrane properties, such as fluidity. That might prevent viruses from efficiently binding to cell surface receptors required for entry, accounting for its anti-viral properties.

Similar effects on membrane fluidity could enhance the release of dopamine and norepinephrine into nerve synapses by allowing the vesicles containing these neurotransmitters to fuse more readily with the cell membrane. Conversely, amantadine might be slowing down the re-uptake of DA and NE from the synaptic space.

Just having fun speculating!

Robert