Sulfisoxazole

Sulfisoxazole is a sulfonamide antibiotic that has historically been used to treat various bacterial infections. It works by inhibiting bacterial dihydropteroate synthase, a key enzyme in the synthesis of folic acid, thereby blocking production of nucleic acids and limiting bacterial growth. It is considered bacteriostatic rather than bactericidal.

The drug has activity against certain Gram-positive cocci and some Gram-negative bacteria, but its spectrum is limited and resistance to sulfonamides is common in many pathogens. Because of this, sulfisoxazole is no longer a first-line agent for many infections and its use has declined in favor of safer or more effective alternatives. It has been used in combination products, such as Pediazole, which pairs sulfisoxazole with erythromycin, for pediatric respiratory infections and otitis media in the past.

Pharmacokinetically, sulfisoxazole is administered orally and is relatively well absorbed. It distributes into body fluids and tissues and is excreted primarily by the kidneys. Adequate hydration is advised during therapy to reduce the risk of crystalline precipitation in the urinary tract.

Common adverse effects include rash, fever, and other allergic reactions; gastrointestinal upset and photosensitivity may occur. More serious but rare effects can include hematologic abnormalities and nephrotoxicity. Sulfonamides can cause hypersensitivity reactions and may worsen or unmask existing conditions in susceptible individuals. In newborns and in late pregnancy, sulfisoxazole can displace bilirubin and raise the risk of kernicterus; therefore use is avoided in these populations.

Sulfisoxazole should be used only when clearly indicated, with attention to potential allergies and drug interactions. Its role in contemporary practice is limited, and many guideline-driven treatments favor alternative antibiotics.