Tetrasykliinit

Tetrasykliinit, known in English as tetracyclines, are a class of broad-spectrum antibiotics produced by actinobacteria, primarily Streptomyces species. They share a common four-ring core structure known as the naphthacene nucleus, which underpins their chemical properties and antimicrobial activity. The first tetracycline was discovered in the 1940s, and numerous semisynthetic analogues have since been developed to optimize pharmacokinetics and safety.

The primary mechanism of action is reversible inhibition of bacterial protein synthesis. Tetracyclines bind to the 30S ribosomal subunit, blocking the attachment of aminoacyl-tRNA to the ribosome and thereby inhibiting elongation of the nascent peptide chain. This action is generally bacteriostatic rather than bactericidal. The compounds are active against a wide range of organisms, including many Gram-positive and Gram-negative bacteria, as well as atypical pathogens such as Chlamydiae, Mycoplasma, Rickettsiae, and some spirochetes.

Clinical uses include treatment of acne, respiratory and intra‑abdominal infections, and sexually transmitted infections, as well as diseases caused by atypical pathogens and certain tick-borne illnesses. Doxycycline and minocycline are among the most commonly used tetracyclines due to favorable pharmacokinetic properties.

Pharmacokinetics and safety considerations: many tetracyclines are orally absorbed but can form chelates with divalent cations, reducing absorption; taking them with a full glass of water and avoiding calcium- or iron-rich meals near dosing improves intake. They can cause photosensitivity, and their use in children under about eight years of age and during pregnancy is generally avoided due to tooth discoloration and effects on bone development. Resistance arises through efflux pumps and ribosomal protection proteins, and cross-resistance can limit effectiveness within the class.