Maggot cure. I need to find a maggot cure for my 4 year old male labrador retriever.?

My 4 year old labrador was just taken to the vet, he had a maggot infestation on his hind leg. the vet managed to remove most of the maggots, but unfortunately there would still be some maggots that have gone into the dog's body(which cant be removed). the vet had also given some cream. My dog lives outside of our house, he is anot allowed inside. Is there any cure or good medication that i can give my dog, to probably kill the maggots that are in him? or any medication to relieve his pain?