I found this right now in old posts
by Aleda M Cheng, D.V.M., C.V.A, Sep 28, 2007 06:55PM
The dose for benadryl is 1 mg.per pound. A 12 pound dog can take 1/2 of a 25 mg adult human benadryl tablet. A 25 pound dog can take 1 adult size human benadryl etc. Only breeds below 12 pounds need pediatric benadryl. Benadryl can be taken 3 to 4 times per day.
What breed of dog is he? I have heard for instance that Bulldogs suffer commonly with allergies.
It might be helpful to try him with a dose of childrens Benadryl. I am really not sure of the dose. I'll take a look in the archives (I seem to remember a post about that sometime last year) and post back if I find out anything about dosage.
Another thought is -could he have something either embedded or stuck in between the pads of his feet? Take a careful look at his feet, to see if anything is there.