I'm sure some will think this is one of those old wives tales, but it sure doesn't hurt to try.
Our kittens that we got from the pound in November came down with Ringworm diagnosed late December. I spent a week putting on the vile stuff from the vet, and then a rancher's wife overheard me talking to my friend in the line at the grocery store, and she told me to bathe the cats and ourselves ("shampoo" with it too) in buttermilk. She swore by it (and she was really old so I figured she might know what she was talking about). Said that was the only thing they used on the ranch for ringworm. Ever.
So we got out of line and went to the back of the store and added cartons of buttermilk to my basket! We "dipped" the cats in buttermilk only once, and I didn't rinse it out very well, which may be the key, actually. We towel dried the cats and then left them to sit in the sunny spot by the front door for an hour. Their hair dried all clumped together and stiff, but by the next morning they had licked themselves "rinsed" and their hair was soft and silky again.
So, that was early January. It's late March now, and every bit of their fur has grown back. I had three ringworms on my arms and legs, my daughter and one of my two sons had one ringworm each on their torsos. The other son didn't get anything. I never did treat the house or carpets (except to vacuum alot) and I consider our outbreak cured.
Like I said. Buttermilk won't hurt you to "shampoo" with. You might even try not rinsing it out for a couple of hours, and then only rinsing with water. ???
Good luck with whatever you try, and I'm sure some other members will come along soon to add their own success stories.
ETA: Oh yeah. I did heat up the buttermilk in a huge plastic bowl just a tiny bit to take the edge off before I ladeled it over the cats. HTH