Sulfonamides (also called sulfa drugs) are a group of broad spectrum and action antibiotics derived from sulfanilamide. The first class of antibiotics discovered, they stop the growth and replication of bacteria by preventing bacterial folic acid synthesis. Sulfonamides can be prescribed to patients with cystic fibrosis (CF), but their use has diminished with newer and more effective antibiotics.

History of sulfonamides

Sulfonamides were discovered in 1932 and put into clinical use by Gerhard Domagk in 1935, providing the first effective therapies for many bacterial diseases of that time. Since then, they have been extensively used in many different clinical indications.

The first sulfonamide, Prontosil, was a red dye that Domagk found effectively treated bacterial infections in mice. It had a strong protective action against in vivo infections because, when metabolized in the body, the dye released a colorless and active antibacterial compound called sulfanilamide. It was this compound that led to various forms of sulfa drugs being produced. Although the introduction of antibiotics like penicillin diminished reliance on sulfonamides, they continue to be used to treat bacterial infections, including Streptococcal infections, urinary tract infections, and ulcerative colitis.

How sulfonamides work

This group of antibiotics are chemical analogues of p-aminobenzoic acid (PABA) that interfere with folic acid synthesis. They work by binding and blocking a specific enzyme, dihydropteroate synthase (DHPS), that is essential for the synthesis of folate, a vitamin bacteria — like all living organisms — need to survive. Folate synthesis depends on a chemical reaction between two molecules, DHPP and PABA, and that reaction is brought about by DHPS.

Sulfonamides and cystic fibrosis

Sulfisoxazole and the combination of erythromycin/sulfisoxazole are two types of sulfa drugs used to treat Pseudomonas aeruginosa and Staphilococcus aureus infections in people with CF. They are taken orally, every six hours for about 20 days.

Sulfisoxazole may cause dizziness, drowsiness, headache, gas, loss of appetite, sensitivity to sunlight, and vomiting.

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