Tetracyclines

These drugs are primarily used as antibacterial agents, but they do have activity against some parasites (notably malaria). The commonest formulation is doxycycline.

Mechanism of action

These drugs also act by inhibiting protein synthesis at the level of the ribosome.

Route of administration

Tetracyclines are most often administered either orally or topically. Intravenous forms are available, but are very seldom used, since if patients are sick enough to require intravenous therapy, there are usually alternatives available.

Spectrum of action

Tetracyclines have a wide spectrum of activity – being active against a range of both Gram positive and Gram negative bacteria. Unfortunately, many organisms are now resistant to this class of antibiotic, and it is thus not recommended therapy for many infections. However, there are some situations where tetracyclines are appropriate, and they are the therapy of choice for tick bite fever, brucellosis, cholera and some chlamydial infections (one of the causes of genital ulcers). They are also used as alternative agents for treating syphilis, Mycoplasma pneumoniae, and some mycobacterial infections.

Side effects

The most important side effect of tetracyclines is damage to growing bones and teeth, and should thus not be used in children or pregnant women, unless there is no alternative.