Antibiotics

PHARMACOKINETIC FEATURES

After usual oral dosage, tetracyclines are absorbed primarily in the upper small intestine, Gl absorption can be impaired by sodium bicarbonate, aluminum hydroxide, magnesium hydroxide, iron, calcium salts, and (except for the liqid-soluble tetracyclines doxycycline and minocycline) milk and milk products.

Tetracyclines at therapeutic concentrations should not be administered PO to ruminants: they are poorly absorbed and can substantially depress ruminal microfloral activity.

Through chemical manipulation (especially choice of carrier and high magnesium content), the absorption of oxytetracycline from IM sites may be delayed, which produces a long- acting effect.

Tetracyclines can cause tissue necrosis at injection sites, in which residues may remain for several weeks.

Tetracyclines can also be absorbed from the uterus and udder, although plasma concentrations remain low.