It is best not to apply amoxicillin externally to a dog's wound, because amoxicillin is an internal medicine. If applied externally to a dog's wound, it may cause irritation to the dog or even produce adverse reactions, so it is not recommended to give it to the dog. Topical amoxicillin for dogs. If your dog is injured, it is best to clean the wound first, then apply iodine for disinfection, and finally use a special external dressing to bandage it.