For the wash: DVM Chlorhexidine (4%) shampoo (Hibiclens found at Walgreens, etc. is also 4% and works well, too.) Lather, let stand for 10 minutes, rinse and dry leg thoroughly.
Topical: generic monistat (miconozole nitrate--way cheaper). Smear onto the area and rub in. If desired, cover the monistat area over with either Desitin or Balmex as well for faster results.
That's what I got from my vet. It works very well, but is only one of the recipes out there to choose from.
i used just desitin on my mare, as she is sensitive to many things. It seemed to clear it up very quickly and she wasnt sensistive or allergic to it and it stayed on pretty well through riding, rain, and turnout
I had a mare and we have currently a gelding where the above works best but I just wanted to share that my older TB used to have bad scratches and a vet spent a lot of time helping me attack them because his leg kept swelling up - but we found through all the effort that it was the aggression that was doing it. FOR HIM what I had to do was clean the area every day or at leaste every other day with a tea tree shampoo and then on the non cleaning days pour listerine on them. Anything else was too much for his skin and he would blow up with a skin inflamation due to reaction to the chemicals.
I have a horse that had persistent scratches and I finally used a product called Tea-Clenz. It has Tea Tree Oil in it. You just spray it on (or use it as a rinse for rainrot) and leave it on. It works great.
BTW, it comes in a 16 oz container, but you mix it 1 oz to 1 gallon of water.
If I remember correctly, the scratches receipe that I use (a CoTH receipe) is equal parts destin, neosporin and athlete's foot cream. I use the generics of all (if available). Just mix well in a separate container and apply as needed.