Allergic reaction to Bactrim?

I was put on Bactrim for a sinus infection on April 18,2011. On April 24, 2011 I broke out in hives. I finished the course of Bactrim on 4/28/2011. Since then I break out in hives every once in awhile and I have the "itchies". On May 17, 2011, I went to the doctor who also thought that this was due to the Bactrim. He put me on a six day course of Prednisone which I finished yesterday. Today, again, I am breaking out in hives and have the itchies again which I didn't have when I was on the Prednisone. How long is this going to last? Should I go see an allergist? Please help.
Thanks

[Bhupinder Kaur, MD]

Hello,
What you are having is hives and hives may be triggered by viral infections or medications. It can be triggered by Bactrim in your case. You can take some OTC oral antihistamine medications like Benadryl or Claritin and see if it helps. Application of calamine lotion on the rash and taking vitamin C supplements or vitamin C rich foods like citrus fruits are also helpful. If the symptoms persist then you may need topical or oral steroids for which you have to consult a dermatologist.

It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.