I've used this before (from Pete Ramey's website). It worked great.
For years I've searched for the perfect thrush medicine. Most products that kill the fungi and bacteria also kill living tissue; contributing to the problem. I use a 50/50 mix of Triple Antibiotic Ointment and Athletes Foot Cream (1% Clotrimazole) (for humans; over the counter at any pharmacy). I mix it thoroughly and put it in a 60cc catheter-tip syringe (available from any vet) (The syringe may well be more important than the cream, as it allows deep penetration to the core of the problem). Mix the products in a Tupperware bowl, then spoon in or 'top load' 15cc with a butter knife. I have my horse owners treat deep into central cleft daily until no cleft is present. No need to squirt it all over the frog; just a pea-sized dab at the very bottom of the central sulcus. To date, I've seen it eliminate deep, sensitive central frog clefts in 100% of cases within 2 months. (A first, with every treatment I've ever used, though past experience tells me we'll never find a product that works on every case in every environment.)