Ciprofloxacin injection is used to treat certain infections caused by bacteria. Ciprofloxacin injection is also used to prevent or treat anthrax (a serious infection that may be spread on purpose as part of a bioterror attack) in people who may have been exposed to anthrax germs in the air. Ciprofloxacin injection is in a class of antibiotics called fluoroquinolones. It works by killing bacteria that cause infections. Antibiotics will not work for colds, flu, or other viral infections.