Tetracyclines act bacteriostatically on rapidly dividing bacteria by inhibiting protein synthesis. Their binding to the 30S subunit of the ribosomal complex blocks the attachment of tRNA to the complex. This group (doxycycline and tetracycline) is used in treatment of a wide range of infections including both Gram-positive and Gram-negative bacteria. However it has been found to be especially useful in the treatment of Lyme’s disease, Legionella and Chlamydia infections. Tigecycline is the newest tetracycline indicated for complex skin infections.

Tetracyclines are chelated with cations; therefore their oral absorption is decreased. The tetracyclines have a strong affinity for developing bone and teeth resulting in an irreversible yellow-brown colouring. Other side effects of tetracycline therapy are GI problems, photosensitivity (pigmentation of the skin after exposure to sunlight).


A 21-year old man suffers from sepsis with Staphylococcus aureus. The drug of choice is doxycycline.


Tetracyclines are considered safe in pregnancy.