tetracicline

Tetracycline is a class of broad‑spectrum antibiotics that inhibit bacterial protein synthesis. They bind reversibly to the 30S ribosomal subunit, blocking the attachment of aminoacyl‑tRNA and preventing elongation of the nascent protein. Most tetracyclines are bacteriostatic; resistance commonly arises through efflux pumps, ribosomal protection proteins, or enzymatic inactivation.

Discovered in the 1940s, the tetracycline family includes first‑generation tetracycline as well as semisynthetic analogs such as doxycycline and minocycline. The core four‑ring naphthacene structure is conserved across the group and determines their pharmacokinetic properties.

Clinical use covers a broad spectrum, including many Gram‑positive and Gram‑negative bacteria, as well as atypical pathogens such as Mycoplasma, Chlamydia, and Rickettsia. They are employed for acne, respiratory and urinary tract infections, and certain vector‑borne diseases. Doxycycline is commonly used for Lyme disease, Rocky Mountain spotted fever (RMSF), Q fever, and malaria chemoprophylaxis in endemic areas.

Pharmacokinetics varies by agent. Most are orally active, but absorption of older tetracyclines is reduced by divalent cations and some foods. Doxycycline and minocycline have favorable absorption and longer half‑lives, supporting once‑ or twice‑daily dosing. Excretion routes depend on the drug, with renal and hepatic pathways both involved.

Safety considerations include gastrointestinal upset and photosensitivity. Tetracyclines are contraindicated in pregnancy and in children under eight due to tooth discoloration and enamel hypoplasia. They can cause esophageal irritation if not taken with adequate water, and chelate with calcium, iron, and aluminum, reducing absorption of the drug or supplements.

Resistance is an ongoing concern, with mechanisms such as efflux, ribosomal protection, and enzymatic inactivation. Regulatory and stewardship measures limit inappropriate use, including restrictions on agricultural applications in some regions.