What can i do if my knuckles broke out in hives, how many benadryl (diphenhydramine) do i take?

Start with 50mg: This is a starting dose - it can take 15-20 minutes to help. Some pills come as 25mg others as 50 mg over the counter so check that to see if you need 1 or 2. If the hives spread or become more severe take another 50 mg but get to the er! in a localized area that is small like your knuckles you could also apply topical hydrocortizone cream to the area or there is also a Benadryl (diphenhydramine) cream too.