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. Doxycycline is excreted mainly in the feces. All tetracyclines are partially excreted in bile, resulting in high biliary levels, from which they are then partially reabsorbed.