Sulfa allergy: Which medications should I avoid?

I have a sulfa allergy. How can I tell if a medicine contains sulfa? Antibiotics containing chemicals called sulfonamides can trigger a reaction if you have a sulfa allergy. Examples of sulfonamide antibiotics include the combination drug trimethoprim-sulfamethoxazole (Septra, Bactrim). Other types of sulfa medications may trigger a reaction in some people who have a sulfa allergy. . read more.