Yes, Posatex needs a prescription as it is a medication that is a combination of three powerful drugs. It is always better to consult with your vet before administering Posatex. The vet will be able to guide you about the dosage required after examining your dog's condition. If Posatex is taken based on prescription, otitis externa gets cured under 7-10 days. The pain reduces quickly once the treatment starts. External Otitis is not transmissible. Therefore, you can take your dog if he is feeling better for a regular outing. Never experiment yourself on your pet dog. It saves your dog from different side effects that can occur if you give the medication without the prescription from your vet.