Used to treat a wide range of bacterial infections, including respiratory tract infections, urinary tract infections, meningitis, and gastrointestinal infections caused by susceptible bacteria. Effective against both Gram-positive and some Gram-negative organisms. Commonly administered in clinical settings for patients with infections where penicillin-sensitive pathogens are present. Also used in veterinary medicine and in laboratory settings for selection in cell culture and microbiology work involving antibiotic-resistant markers.