These drugs are closely related bacteriostatic antibiotics, similar in antibacterial spectrum and toxicity. They bind to the 30S subunit of the ribosome and thus inhibit bacterial protein synthesis. Serious staphylococcal disease should not be treated with tetracycline. Bacterial resistance to one tetracycline indicates likely resistance to the others. The tetracyclines are variably absorbed after oral administration.
Food interferes with absorption of tetracyclines, with the exception of doxycycline and minocycline.
Absorption of tetracyclines is decreased with antacids containing aluminum, Ca, and Mg and with preparations containing iron. Tetracyclines penetrate into most tissues and body fluids. However, CSF levels are not reliably therapeutic. Minocycline, because of its high lipid solubility, is the only tetracycline that penetrates into tears and saliva in levels high enough to eradicate the meningococcal carrier state. All tetracyclines, except doxycycline, are excreted primarily in the urine by glomerular filtration, and their blood levels increase with renal insufficiency.