I Have A Rash And Hives Due To A Cream

I have a rash and hives due to a cream containing sulfa drug being massaged into scar tissue from my TKR. This reaction started 4 wks ago and still causes extreme itching in areas where the cream was not used. I have a prescription and have been told to take 3 300mg capsules of clindamycin 1 hr before my dental cleaning tomorrow, Will this possibly aggravate the allergic reaction I am trying to overcome?