Hello, There is no way to know whether you re allergic to something unless you try it out. It doesn t make much difference that some of your family members are allergic to sulfa drugs. There is something important to consider though. If you ve ever had a serious allergic reaction to anything then you should be very cautious with any new drug you re about to try. By serious I mean any of the following symptoms that required a visit to the ER and perhaps admission to the hospital: - shock (low blood pressure and organ dysfunction) - airway involvement (stridor, Ronchi, swollen lips, tongue, etc) with or without shortness of breath. If you ve never had a serious reaction in the past then there is no reason to avoid the drug. Otherwise you should discuss these concerns with the treating doctor. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Panagiotis Zografakis, Internal Medicine Specialist