Doxycycline injection is used to treat or prevent bacterial infections, including pneumonia and other respiratory tract infections. It is also used to treat certain skin, genital, intestine, and urinary system infections. Doxycycline injection may be used to treat or prevent 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 in the air. Doxycycline injection is in a class of medications called tetracycline antibiotics. It works by killing bacteria that cause infections. Antibiotics such as doxycycline injection will not work for colds, flu, or other viral infections. Taking or using antibiotics when they are not needed increases your risk of getting an infection later that resists antibiotic treatment.