There are hundreds of different rumors about creatine. One "research" will tell you that it's going to cause you to have liver problems; the other tells you you're going to grow an extra head. So to say that Creatine is "toxic" in liquid form I don't know for sure, but it certainly loses any gain you might have gained in powder form. A few years ago, back before the "energy drink" fad that's recently shown up, I had seen an energy drink in New York for young girls that had Creatine in it!
Honestly, if your kidneys are hurting it might be time to back up on energy drinks anyway, not just the creatine. I've seen one energy drink (tasted great, blue bottle, bumps on it) in which it had a whole lists of warnings not to take it.
On another note, how do you know it's your kidneys? Did you ask em?