Sulfa allergy: Which medications should I avoid?

The term "sulfa allergy" is most often used to describe an adverse drug reaction to the antibiotic sulfamethoxazole, an ingredient in sulfonamide-containing antibiotics, such as Septra and Bactrim. If you have a sulfa allergy, you should avoid all such medications. You should also avoid the antibiotic Pediazole, which contains sulfisoxazole — an ingredient closely related to sulfamethoxazole.

Sulfur, sulfites and sulfates are generally not closely related to sulfamethoxazole and are unlikely to cause adverse effects in people with a sulfa allergy. However, there are many medications that are distantly related to sulfamethoxazole, including certain diuretics, such as hydrochlorothiazide; oral diabetes medications, such as sulfonylureas; and some nonsteroidal anti-inflammatory drugs, such as celecoxib (Celebrex). Although these medications are probably safe for you to take if you have a sulfa allergy, you should first check with your doctor.

Some drug names may not sound like they're related to sulfamethoxazole when, in fact, they are. So, avoiding only medications with the prefix "sul" or even "sulfa" is not a good rule of thumb if you have a sulfa allergy.