How to treat a dog with a plastered leg?

I have a one year old dog. He broke his front foot while playing. Now his leg is plastered but the vet doc says that some kind of infection has entered his plaster at the lower foot portion. If the infection is not treated then they will cut his foot. Pls... any suggestions about how to treat his infected foot... are welcome. The doctor has suggested to dry the lower portion of the plaster with a hair dryer and then to sprinkle some anti-fungal powder on it. Please help!