Tetracyclines

- Tetracycline

- Doxycycline

- Minocycline

The antimicrobial spectra of all tetracyclines are nearly identical. They have activity against Gram-positive coccal. Escherichia coll. Neisseria gonorrhoeae, Brucella spp., vibrios. rickettsiae, mycoplasmas, chlamydiae and spirochaetes, including Tre­ponema pallidum and Borrelia burgdorferi.

This is the treatment of choice for chlamydial, rickettsial, brucella and ureaplasma infections and is an alternative to erythromycin for Mycoplasma pneumoniae. Tetra­cyclines are also used for the treatment of inflammatory acne. Both doxycycline and minocycline have long half-lives and are therefore given once daily or twice daily. Unlike most other tetracyclines, they are reliably absorbed in the presence of food. Tetracyclines are contraindicated in children less than 8 years of age and in preg­nancy (except for serious rickettsial and brucella infections) as they discolor develop­ing teeth and may depress skeletal growth in premature infants. Only doxycycline can be used safely in renal insufficiency, and this agent is also less likely to stain the teeth. Gastrointestinal side effects and photosensitivity are relatively uncommon with all tetracyclines; vertigo is common with minocycline.