Tetracyclines

Tetracyclines are a class of broad‑spectrum antibiotics derived from Streptomyces species, including tetracycline, doxycycline, minocycline, demeclocycline, and oxytetracycline. They are bacteriostatic and inhibit protein synthesis by reversibly binding to the 30S ribosomal subunit, blocking aminoacyl‑tRNA binding.

Spectrum and uses: They act against many Gram‑positive bacteria, many Gram‑negative bacteria, and atypical pathogens such as Chlamydiae, Mycoplasma, and Rickettsiae, and some spirochetes (Borrelia). Clinical uses include acne and rosacea, chlamydial and rickettsial infections, Lyme disease, and Helicobacter pylori regimens. Doxycycline is also used for malaria prophylaxis in travelers.

Pharmacokinetics and administration: Doxycycline and minocycline have good oral bioavailability and can be taken with meals (though calcium/iron supplements may reduce absorption for some agents); tetracycline absorption is reduced by food and dairy. Doxycycline is often preferred in renal impairment. Most tetracyclines are eliminated to varying extents by the kidneys and liver. They can cause esophagitis if not taken with water and photosensitivity; pregnancy and young children should avoid due to teeth discoloration and enamel defects.

Resistance and safety: Resistance mechanisms include efflux pumps and ribosomal protection proteins. Drug interactions include chelation with calcium, magnesium, iron, or aluminum‑containing preparations, reducing absorption.

History and note: The tetracycline class was developed in the mid‑20th century from Streptomyces; tetracycline was introduced in the 1940s. Tigecycline, a glycylcycline related to tetracyclines, was developed to counter resistance and is used for complicated infections.