Benadryl Dosage for Dogs. As far as Benadryl dosage for dogs, it is always recommended that owners start at the lower end of the dose range and work their way up as needed. This is often referred to as âtitrating the medication to effectâ.The Benadryl dosage for dogs and cats is 1-2 mg per pound of body weight administered every 8-12 hours as needed. It should be administered orally, approximately one hour prior to a potentially stressful event (a car ride for example).edium dogs are started on a Benadryl dosage for dogs at 1/2-3/4 of the 25mg tablet. And so onâ¦). As is true of many medications, the animalsâ individual body chemistry and genetics will determine its response to a particular drug.