Benedryl can be given at a dose of 1-2 mg/lb, where the 2mg/lb dose is appropriate to head off anaphylactic responses to such things as bee stings, or in my Barney's case- yellow jacket stings.

Typically for my lab of 75 lbs when she got into allergy seasons (e.g. Spring/Fall) I would give her 25 mg in the morning and 50 mg at night. Warning: Benedryl will make puppy SNORE!