Doxycycline is an antibiotic medicine belonging to the class called "tetracyclines." Doxycycline is a broad-spectrum antibiotic synthetically derived from oxytetracycline and is available as doxycycline monohydrate; doxycycline hyclate; doxycycline hydrochloride hemiethanolate hemihydrate; and doxycycline calcium for oral administration. Doxycycline is a light-yellow crystalline powder. Doxycycline hyclate is soluble in water, while doxycycline monohydrate is very slightly soluble in water.
Doxycycline is used to treat bacterial infections, including pneumonia, lyme disease, acne, venereal (sexually transmitted) diseases, and inhalational anthrax (after exposure). It also is used to prevent malaria. Doxycycline is a broad-spectrum tetracycline antibiotic used against a wide variety of bacterial infections, including Rocky Mountain spotted fever and other fevers caused by ticks, fleas, and lice; urinary tract infections; trachoma (chronic infections of the eye); and some gonococcal infections in adults. It is an approved treatment for inhalational anthrax. It is also used with other medications to treat severe acne and amoebic dysentery (diarrhea caused by severe parasitic infection of the intestines). It is also used for severe acne, as it is active against the bacteria associated with acne, Propionebacterium acnes. This is a common type of bacteria that feeds on sebum produced by the sebaceous glands in the skin. It produces waste products and fatty acids that irritate the sebaceous glands, making them inflamed and causing spots. By controlling bacterial numbers, doxycycline brings the inflammation of the sebaceous glands under control, and the skin is allowed to heal.
Of all the older antibiotics, doxycycline has the greatest potential for expanded use. The spectrum of activity determines, in large part, the application of an antibiotic, and doxycycline's lipid solubility and intracellular mode of action give it an unusually wide spectrum of activity. Its long half-life permits once- or twice-daily dosing. It has excellent bioavailability, and blood and tissue levels are equivalent whether the drug is administered orally or intravenously. Recently, doxycycline has been found to be effective for unusual diseases that are being seen with increasing frequency and for diseases that have just been discovered in the last few decades.