Several medicines are sulfa based and can cause problems for people allergic to sulfa drugs. The main culprits are the carbonic anhydrase inhibitors used for glaucoma. Examples of these glaucoma drops include dorzolamide, Trusopt, Azopt, and Cosopt. Also, the water pill Diamox (acetazolamide) is sometimes used for treating advanced glaucoma, but is sulfa-based as well. Sulfacetamide is an antibiotic eye drop (also called Bleph-10) that can also cause sulfa problems, but I rarely prescribe this, given the plethora of good antibiotic alternatives.