I too reacted terribly to Levaquin, many years ago, but I am SO sensitive so quickly to porphyrogenic medicines that I gave up Levaquin after one dose. On this pill (one), I was so spastic that I could not go around corners, and immediately lose all color vision. Now these symptoms were not really bad, compared to some I've had (like temporary paralysis from taking one Elavil), but they allerted me to the utter folly of continuing with Levaquin.
When I took the Levaquin, I had only an MS dx, but not too long after that I was dx'd with Porphyria, and this helped me know which drugs I could not take, and which other things I needed to avoid.
I too MUST take 1000 mg of Magnesium per day to stop spasticity and jerkiness. I would run not walk to the health food store or the natural foods section of your supermarket. Almost any magnesium will "work" to aid this type of nerve problem (including the burning of PN), but my neuro who prescribed Mag many years ago, when I could not take Baclofen or Zanaflex, said to find one that causes the least diarrhea. I do have some diarrhea but it has not been bad until recently, so now I am experimenting with altering the type of mag I take. I am taking half Mag Taurate and half the previous supplement, which was a combo of Mag types. The Mag Taurate is more expensive but I figure after all these years I better help myself when it's possible. My diarrhea is improving on this.

I have to take other things to help the PN in my legs and lower back, as I get older. I also must be sure to have 1000 mg of Calcium a day (which I usually take at a different time than the Magnesium (Mag with meals, Calcium between). I take 100 mg of B1 per day, which potentiates magnesium. I take Vitamin E complex from the health store. If I miss any of these things, burning pain around calf, jerking, leg going into spasticity.

These things may not fix the situation completely but they could help.