Tetracycline: A family of broad-spectrum antibiotics effective against a remarkably wide variety of organisms. Bacteria susceptible to tetracycline include H. flu (Haemophilus influenzae), strep (Streptococcus pneumoniae), Mycoplasma pneumoniae, Chlamydia psittaci, Chlamydia trachomatis, and Neisseria gonorrhoeae (the cause of gonorrhea). Tetracycline is also used to treat nongonococcal urethritis (due to Ureaplasma), Rocky mountain spotted fever, typhus, chancroid, cholera, brucellosis, anthrax, and syphilis. It is used in combination with other medications to treat Helicobacter pylori, the bacteria associated with ulcers of the stomach and duodenum.
Tetracycline can have toxic effects on development of bone. Therefore, tetracyclines are generally not recommended during pregnancy or nursing. Tetracyclines may cause discoloration of teeth if used in children less than 8 years of age.