You should try some honey based wound ointment.
They should have it at your vets or at a pharmacy.
It's called Dermiel here in Holland, but i don't know how it's called in the USA.
It does wonders for wounds! We had a leachie who had a hole eating into him by fruitfly maggots and it healed perfectly in a few months (leaving some scarring behind, but that's normal).
Good luck!!
Best regards,
Léon and Debbie
www.the-gex-files.nl