Oxytetracycline works by interfering with the ability of bacteria to produce essential proteins. Without these proteins, the bacteria cannot grow, multiply and increase in numbers. Oxytetracycline therefore stops the spread of the infection and the remaining bacteria are killed by the immune system or eventually die.

Oxytetracycline is a broad-spectrum antibiotic, active against a wide variety of bacteria. However, some strains of bacteria have developed resistance to this antibiotic, which has reduced its effectiveness for treating some types of infections.

Oxytetracycline is used to treat infections caused by Chlamydia (e.g. the chest infection psittacosis, the eye infection trachoma, and the genital infection urethritis) and infections caused by Mycoplasma organisms (e.g. pneumonia).

Oxytetracycline is also used to treat acne, due to its activity against the bacteria on the skin that influence the development of acne (Cutibacterium acnes). It is used to treat flare-ups of chronic bronchitis, due to its activity against the bacteria usually responsible, Haemophilus influenzae. Oxytetracycline may also be used to treat other rarer infections, such as those caused by a group of micro-organisms called rickettsiae (e.g. Rocky Mountain spotted fever). To make sure the bacteria causing an infection are susceptible to it, a tissue sample is usually taken, for example a swab from the infected area, or a urine or blood sample.

Oxytetracycline was patented in 1949 and came into commercial use in 1950.[1] It is on the World Health Organization’s List of Essential Medicines as an alternative to tetracycline.

Oxytetracycline, like other tetracyclines, is used to treat many infections, both common and rare (see Tetracycline antibiotics group). Its better absorption profile makes it preferable to tetracycline for moderately severe acne at a dosage of 250–500 mg four times a day for usually six to eight weeks at a time, but alternatives should be sought if no improvement occurs by three months.[3]

It is sometimes used to treat spirochaetal infections, clostridial wound infection and anthrax in patients sensitive to penicillin. Oxytetracycline is used to treat infections of the respiratory and urinary tracts, skin, ear, eye and gonorrhoea, although its use for such purposes has declined in recent years due to large increases in bacterial resistance to this class of drugs. The drug is particularly useful when penicillins and/or macrolides cannot be used due to allergy. It may be used to treat Legionnaire’s disease as a substitute for a macrolide or quinolone.

Oxytetracycline is especially valuable in treating nonspecific urethritis, Lyme disease, brucellosis, cholera, typhus, tularaemia. and infections caused by Chlamydia, Mycoplasma and Rickettsia. Doxycycline is now preferred to oxytetracycline for many of these indications because it has improved pharmacologic features.

The standard dose is 250–500 mg six-hourly by mouth. In particularly severe infections, this dose may be increased accordingly. Occasionally, oxytetracycline is given by intramuscular injection or topically in the form of creams, ophthalmic ointments or eye drops.