The first quinolone (quinol[ine] + -one [compoundrelated to ketone]), nalidixic acid, was isolated as a byproduct of chloroquine (see “quinine”) synthesis and was introduced in 1962 to treat urinary tract infections. In 1980, researchers at the Kyorin Pharmaceutical Company showed that the addition of a fluorine atom to the quinolone ring resulted in an antibiotic with broader antimicrobial activity, which was named norfloxacin, the first fluo-roquinolone. In 1983, Bayer published data that showed adding a single carbon atom to norfloxacin—what would become ciprofloxacin—further increased activity. Fluoroquinolones are today among the most frequently used anti-microbial drugs to treat infections in humans and animals.