Sulfa Allergy: Cross-reactivity versus Multiple Concurrent Allergies

As a medical resident we have always been taught that there is some sort of cross reactivity between sulfonamide antibiotics and nonantibiotic sulfonamides. Even the manufacturer’s package inserts contain a precautionary statement about possible Cross-reactivity. The most common approach to this problem is avoidance of all sulfa containing drugs. However, there are few data supporting this contraindication. Thus we may be withholding appropriate therapies from patients unnecessarily. To provide a critical and comprehensive review of literature to explore either cross reactivity between sulfonamide antibiotics and nonantibiotic sulfonamides is a fact or fiction and to present an approach to use nonantibiotic sulfonamides in sulfa allergic patients. A PubMed and general medline search was conducted using the individual names of nonantibiotic sulfonamides. We reviewed all of the available case reports and studies regarding sulfonamide antibiotic cross-reactivity with nonantibiotic sulfonamides. Also reviewed the manufacturer’s package insert for each nonantibiotic sulfonamide drug for information concerning possible cross-reactivity with sulfonamide antibiotics. Sulfa drug allergy is one word holding the whole cross-reactivity theory in it. It should be obsolete from the medical dictionary. This one word is complicating the medical decision-making. Allergies should not be attributed to classes or groups of drugs unless proven. After reviewing all the available literature we can conclude that assumptions about cross-reactivity are a FICTION.