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Unfortunately, the law prevents us from prescribing any medication unless a relationship has been established and this requires an examination. If you are not near your regular veterinarian, your best bet would be to make an appointment at a local vet in your area to have your dog examined so that the proper ointment can be prescribed.
There is an over the counter antibiotic ointment called Terramycin that should be available at feed stores or pet stores but if your dog needs a different kind of ointment, I am arid that you will have to take him to see a vet.