Mecillinam is primarily used as an antibiotic to treat bacterial infections, particularly those caused by Gram-negative bacteria. It is highly effective against urinary tract infections (UTIs) caused by Escherichia coli and other susceptible pathogens. The antibiotic works by inhibiting bacterial cell wall synthesis, making it a valuable option for infections resistant to other antibiotics. It is often administered orally or intravenously, depending on the severity of the infection. Mecillinam is also used in some cases for the treatment of gastrointestinal infections and respiratory tract infections. Its targeted action and low resistance development make it a preferred choice in specific clinical scenarios.