Sulfisoxazole is a sulfonamide antibacterial antibiotic. The sulfonamides are synthetic bacteriostatic antibiotics with a wide spectrum against most gram-positive and many gram-negative organisms. However, many strains of an individual species may be resistant. Sulfisoxazole acetyl in combination with erythromycin ethylsuccinate is used for treatment of ACUTE OTITIS MEDIA in children that is caused by susceptible strains of Haemophilus influenzae. Sulfisoxazole acetyl is a prodrug of sulfisoxazole. Acetyl group is added to make the drug poorly water soluble, and is hydrolyzed in vivo to the active drug. Sulfisoxazole and its acetylated metabolites are excreted primarily by the kidneys through glomerular filtration. Sulfisoxazole is a competitive inhibitor of the enzyme dihydropteroate synthetase. It inhibits bacterial synthesis of dihydrofolic acid by preventing the condensation of the pteridine with para-aminobenzoic acid (PABA), a substrate of the enzyme dihydropteroate synthetase. The inhibited reaction is necessary in these organisms for the synthesis of folic acid