If one has a sulfa allergy and what would be the medicines to treat this?

There are none. If you are truly allergic to sulfa you must avoid all forms of the drug whether it be in eye drops, pills or IV meds. There is no med to cancel out the allergy and true allergy could lead to life threatening consequences if exposed. It would be wise to invest in a medical alert bracelet to make sure people are aware if you cannot communicate.
Avoid sulfa. Current treatment for medication allergies including sulfa is avoiding that class of medication and use a suitable alternative. If a person is experiencing an allergic reaction to sulfa, stopping the medicine and treatment may include antihistamines, steroids and if potentially even epineprhine if severe.