Phthalylsulfacetamide is primarily used as an antibacterial agent, particularly in the treatment of intestinal infections. It is effective against a range of gram-positive and gram-negative bacteria, making it useful in managing conditions like bacterial dysentery and gastroenteritis. The compound works by inhibiting the synthesis of folic acid in bacteria, which is essential for their growth and reproduction. It is often administered orally, as it is poorly absorbed from the gastrointestinal tract, allowing it to act directly on the pathogens in the gut. Additionally, it is sometimes used in veterinary medicine to treat similar infections in animals. Its targeted action in the intestines helps minimize systemic side effects, making it a preferred choice for localized bacterial infections in the digestive system.