Tetracyclines-extending the atypical spectrum.

The main features and the present position of tetracyclines are reviewed. The mechanism of their action, bacterial resistance and the most recent findings are reported. Their decreased use is due to the availability of new, active, better-tolerated antibiotics. However, tetracyclines still have a place in the treatment of chlamydial and rickettsial infections, brucellosis and Lyme disease. In respiratory infections, they can be employed when necessary in infections caused by Chlamydia psittaci, C. pneumoniae, Mycoplasma pneumoniae, and also by Streptococcus pneumoniae and Haemophilus influenzae, whose rates of resistance now seem lower than in the past when tetracyclines were more largely prescribed.