Tetracyclines are excreted via the kidneys (glomerular filtration) and the GL tract (biliary elimination and directly.

 

Tetracyclines are also eliminated in milk; concentrations peak 6 hr after a parenteral dose, and traces are still present up to 48 hr later. Concentrations in milk usually attain ~50-60% of the plasma concentration and are ofterf higher in mastitic milk.