Tetracycline antibiotics

This article deals with the group of antibiotics known as the Tetracyclines . For the specific antibiotic called Tetracycline, see Tetracycline.

Image:Tetracyclines.png Tetracyclines are a group of broad-spectrum antibioticswhose general usefulness has reduced with the onset of bacterial resistance. However they continue to remain the treatment of choice for some specific indications.

They are so named for their four ('tetra-') hydrocarbonrings ('-cycl-') derivation ('-ine').

History

The first member of the group to be developed was Tetracyclineitself in 1955. The development of many chemically altered antibiotics formed this group.

Indication

Tetracyclines may be used in the treatment of respiratory tract, sinuses, middle ear, urinary tract, intestines and also Gonorrhoea, especially in patients allergic to Beta-lactams and Macrolides, however there use for these indications is less popular than it once was due to widespread resistance development in the causative organisms.

Their commonest current use is in the treatment of moderately severe Acneand Rosacea(tetracycline, oxytetracycline, doxycyclineor minocycline).

Doxycycline is also used as a prophylactic treatment for infection by Bacillus anthracis (anthrax) and is effective against Yersinia pestis, the infectious agent of bubonic plague. It is also used as for malaria treatment and prophylaxis.

They remain the treatment of choice for for infections caused by Chlamydia(Trachoma,Psittacosis, salpingitis, Non-specific urethritisand Lymphogranuloma venereum), Rickettsialdiseases, Brucellosis, Spirochaetal(Borreliosisor Lyme disease). In addition they may be used for Anthrax, Plague, Tularaemia, Legionnaire's disease.

Demeclocyclinehas an additonal use in the treatment of Syndrome of inappropriate antidiuretic hormone.

Administration

When ingested, it is usually recommended that tetracyclines should be taken on an empty stomach with a full glass of water. This is partly due to the fact that tetracycline binds easily with magnesium, aluminium, iron, and calcium, which reduces its ability to be completely absorbed by the body. Dairy products or preparations containing iron are not recommended directly after taking the drug.

Cautions

Tetracyclines should be used with caution in those with liver impairment and may worsen renal failure (except doxycycline and minocycline). They may increase muscle weakness in myasthenia gravisand exacerbate systemic lupus erythematosus. Antacids and milk reduce the absoption of tetracyclines.

Like many antibiotics, they decrease the effectiveness of birth control pills.

Drugs in the tetracycline class become toxic over time, so expired prescriptions of these drugs should be discarded after the expiration date has passed.

Contraindications

Tetracycline use should be avoided in pregnant or lactating women, and in children with developing teeth because it will result in permanent staining of teeth and bones.

Side Effects

Side effects from tetracyclines are not common, but of particular note is possible photosensitive allergic reaction which increases the risk of sunburn under exposure to UV light from the sun or other sources. This may be of particlar importance for those intending to take on holidays long-term doxycyline as a malaria prophylaxis.

They may cause stomach or bowel upsets, and rarely allergic reactions. Very rarely severe headache and vision problems may be signs of dangerous Intercranial Hypertenion.

Mechanism and resistance

Tetracycline inhibits cell growth by inhibiting translation. It binds to the 30S ribosomalsubunit and prevents the amino-acyl tRNA from binding to the A site of the ribosome. The binding is reversible in nature.

Cells become resistant to tetracyline by at least two mechanisms: efflux and ribosomal protection. In efflux, a resistance gene encodes a membrane protein that actively pumps tetracycline out of the cell. This is the mechanism of action of the tetracycline resistance gene on the artificial plasmidpBR322. In ribosomal protection, a resistance gene encodes a protein which binds to the ribosome and prevents tetracycline from acting on the ribosome.

References

• British National Formulary49 March 2005ja:?????????????

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It uses material from the http://en.wikipedia.org/wiki/Tetracycline+antibiotics Wikipedia article Tetracycline antibiotics.