This old class of antibiotics is very rarely used in North America outside of two indications – the long-term suppressive therapy of acne and the therapy of Chlamydia trachomatis STDs.

Three are available – tetracycline, doxycycline and minocycline. Doxycycline is generally the preferred agent owing to pharmacokinetics allowing it to be a once or twice a day drug. It is an underutilized agent in the therapy of respiratory tract infections as an alternative to macrolides. They have similar spectra of activity including anti-“atypical”.

They are contraindicated in pregnancy or childhood as they are incorporated into enamel and discolour teeth.