I'm not SP, but I thought I'd poke around a little to see what's out there on the horizon at least.
Since you're Canadian, sativex (cannabis spray) is approved for use by MS patients. If you're willing to go off the beaten path, and you sound like you are since you're taking doxy, maybe cannabis could be helpful for SPMS. I know it's not exactly the same thing, but this group
in England is doing a trial of cannabis on disease progression for SP patients.
The other SPMS study that seems interesting (also in England, damnit!) is of lamotrigine
, an anti-epilepsy drug that is a sodium-channel blocker. I just mention it as well because it is an approved drug and perhaps could be made available off-label if you don't like any of your other options.
The BioMS trial also sounds interesting. Are you seriously considering it? Does your neuro think it is promising?