Help!! - Allergic Reaction

[Saint Pyr]

We got Otis neutered on Sunday and he is doing good but I think he has had a reaction either to the shaving or the stuff they put on the skin to disinfect.  He is really red and sore looking in that area and is really bugging him as he will just suddenly and frantically jump and start licking and biting the area. The stitches and everything look good but it is all the rest of the area that is really bugging him. I thought that maybe giving him some benadryl might help as I have given it to our horse before but am not sure the dosage for a dog.  I am worried about him as the vet is only in town once a month and has now left.  Is this a good idea and does anyone know doseages??.  He is 9 months old and 98 pounds now.

[London_Pyr_Lover]

My mum's a nurse, and I asked her opinion.  She said if you are going to give a tablet, then about 12.5 mg wouldn't be too much.  The Tablets are 25 mgs each, so half a tablet.  Now this is not ment as medical advise, but merely a hopefully helpful suggestion. 
Hope your boy feels better real soon.

[Saint Pyr]

Thanx guys  .  It is puffy and red like an allergic reaction.  I only have Benadryl Elixir for adults and 1 tsp is 12.5 mg.  So if the doseage for children 6-12 is 1-2 tsp, and he is my baby  then I would be safe giving him say 1 - 1 1/2 tsps as he would be as heavy as say a 10 yo kid??