Ethylhydrocupreine, also known as optochin, is primarily used in clinical microbiology as a diagnostic reagent to identify Streptococcus pneumoniae by its sensitivity in optochin susceptibility tests, distinguishing it from other alpha-hemolytic streptococci. Historically, it was employed as a local anesthetic in dental and medical procedures, particularly for surface and infiltration anesthesia, providing rapid-onset numbing suitable for short procedures. It also exhibits antimicrobial properties that may reduce infection risks in minor interventions. Its clinical use has declined due to toxicity concerns, including potential ocular damage, and the development of safer anesthetics and antibiotics.