I think the most effective treatments for SPS, at least until something better comes along, are those that treat the symptoms that each person has. Oral medications are generally the first line treatments and may be enough for some people.
Agonists for GABA (A & B) should be talked about with your doctor. Benzodiazepines like diazepam, clonazepam, lorazepam, etc., are good GABA (A) agonists for the right people. Baclofen is a GABA (B) agonist. I don't use diazepam or lorazepam except in severe instances as those medications can be more addictive. Diazepam has a half life of roughly 100 hours, clonazepam 30-40 hours, lorazepam 12-18. All can slow or stop a persons breathing, something I already have troubles with.
I use a GABA A and a GABA B agnostic, those being clonazepam and baclofen. The clonazepam serves another purpose for me. With RLS, getting REM sleep is difficult so it helps with that in addition to the RLS medication I take.
Anticonvulsants like gabapentin (aka: neurontin) are used to prevent or control seizures and can also help with nerve pain. I don't use this even though it is also used for RLS (restless leg syndrome) which I do have. I have adverse reactions in that it makes my lymph nodes inflamed. Instead, Depakote & Citalopram works well for me in controlling seizures anxiety and depression and the otherwise constant feeling my throat is seized.
Levetiracetam is another medication for muscle stiffness and life-threatening paroxysmal respiratory spasms. Sometimes it takes trial and error to find the best oral medications or strengths that work best for each individual.
For some people oral medications aren't enough so IVIG treatments may need to be added. There are several types. Having had adverse reactions to at least two types, I was switched to PE (Plasma Exchange.) I had my best results with that but my insurance company stopped allowing it. Now, I do 2 1/2 hour home infusions of Ig (Immune Globulin) that is self-administered subcutaneously. It doesn't work as well for me as the PE but for now it does work to keep me out of full spasm mode for hours at a time until I have a severe episode.