Hi... Sufa drugs are mostly refer to a group of belonging to the class of sulfanamides. There are few other group of drugs that contain sulfur such as few diuretic, antidiabetic medication. and few others which can also cause allergic symptoms.. Occasionally one drug from the class can cause allergic symptoms but another from the same group may not.. Hence only trial of the drug or skin allergen test can help in establishing the allergens.. I guess, it would be the same with ferrous sulfate too.. Contact your doctor for more details...