Sulfasalazine/Azulfadine is one of the older ASA medications (similar to the more commonly prescribed Asacol). It is not an immunosuppresant drug like 6MP. This drug is a combination of sulfapyridine and 5-aminosalicylic acid.
Here's some info that might help:
http://www.scdiet.org/4faq/azulfidine.htmlAfter intially getting worse on Asacol, I asked to be switched to sulfasalazine which is the approved ASA for people following the specific carbohydrate diet. I haven't had any problems with it, but people who do can often be gradually desensitized, as the article above mentions.