Tetracycline

Tetracycline is a broad-spectrum antibiotic in the tetracycline class. It is produced by certain Streptomyces species and has been used since the mid-20th century. It works by reversibly binding to the 30S ribosomal subunit, blocking the attachment of aminoacyl-tRNA and inhibiting bacterial protein synthesis. The drug is generally considered bacteriostatic.

Historically, tetracycline was among the early broad-spectrum antibiotics and became widely used in the ensuing decades. It remains in use in various formulations, although many indications now favor newer tetracyclines with pharmacokinetic advantages.

Tetracycline has activity against a range of organisms, including many Gram-positive and Gram-negative bacteria, as well as intracellular pathogens such as Chlamydia, Mycoplasma, and Rickettsia. It is commonly used for acne, uncomplicated urinary and respiratory tract infections, certain sexually transmitted infections, and diseases caused by intracellular organisms. Resistance is increasing in some settings, limiting its effectiveness for some pathogens.

Pharmacokinetically, tetracycline is given orally but absorption is reduced by polyvalent cations (calcium, magnesium, aluminum, iron) and by some foods. It distributes widely in body tissues and fluids and is excreted in urine and feces. Use is cautioned during pregnancy and in children under eight due to tooth enamel staining and effects on bone growth. Drug interactions with calcium- or iron-containing preparations and antacids can decrease absorption; photosensitivity is a notable adverse effect.

Adverse effects include gastrointestinal upset, esophagitis (if not taken with sufficient water), photosensitivity, and, with prolonged use, candidiasis or other superinfections. Rare cases of intracranial hypertension have been reported. Resistance mechanisms include efflux pumps and ribosomal protection proteins, contributing to reduced utility in some bacterial populations.