Can I use Schluter Kerdi over drywall?

I'm working on tiling a bath, I'm wondering if using Kerdi directly over the drywall will work. Our drywall guy installed drywall everywhere in the bathroom and I thought we were supposed to use something different like hardibacker under the bathroom tile. My question is instead of using a backerboard, can I just use the kerdi directly over the drywall and then tile over that? Thanks for any help :)