Does Furosemide Contain Sulfa?
Yes, furosemide contains a sulfonamide (sulfa) moiety in its chemical structure, but this does NOT mean patients with sulfonamide antibiotic allergies cannot safely receive it. 1
Chemical Structure
- Furosemide is chemically described as 4-chloro-N-furfuryl-5-sulfamoylanthranilic acid, which contains a sulfonamide group 2
- However, the critical distinction is that sulfonamide antimicrobials contain an aromatic amine group at the N4 position—the structural component responsible for allergic reactions—which is absent in non-antimicrobial sulfonamides like furosemide 1
Cross-Reactivity Risk
The 2022 Drug Allergy Practice Parameter explicitly states there is minimal concern for cross-reactivity between sulfonamide non-antimicrobials (including loop diuretics like furosemide) and sulfonamide antibiotics in patients with histories of reactions to sulfonamide antibiotics. 1
- Furosemide is specifically listed in the guideline table of "Drugs with no or weak evidence of cross-reactivity in patients with a history of a sulfonamide antimicrobial adverse reaction" 1
- The structural difference (absence of the N4 aromatic amine group) results in minimal cross-reactivity risk 1
Important Caveats
Rare Case Reports Exist
- One case report from 2006 described a patient with documented sulfonamide antibiotic allergy (trimethoprim/sulfamethoxazole causing pancreatitis) who developed similar symptoms with multiple loop diuretics including furosemide, bumetanide, and torsemide 3
- This patient ultimately required desensitization to furosemide 3
- However, this represents an extremely rare occurrence and does not change the guideline recommendation that cross-reactivity is minimal 1
Clinical Approach
- For patients with documented sulfonamide antibiotic allergies who require furosemide, the drug can generally be administered safely without special precautions 1
- For patients with severe or life-threatening reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis, anaphylaxis) to sulfonamide antibiotics, extra vigilance may be warranted when introducing furosemide, though cross-reactivity remains unlikely 1
- If concern persists in high-risk patients, consider using ethacrynic acid (a non-sulfonamide loop diuretic) as an alternative 3
Other Compounds Without Cross-Reactivity
The following also lack cross-reactivity with sulfonamide antibiotics despite containing sulfur or sulfonamide groups: sulfur, sulfates (ferrous sulfate, magnesium sulfate), and sulfites (sodium metabisulfite) 1