The tetracyclines are used to treat both systemic and local infections. However, resistance and their bacteriostatic nature suggest caution with empirical use for bacterial infections, particularly in dogs and cats. Specific indications include infectious keratoconjunctivitis in cattle, chlamydiosis, heartwater, anaplasmosis, actinomycosis, actinobacillosis, nocardiosis (especially minocycline), ehrlichiosis (especially doxycycline), elimination of Wolbachia (ie, as part of the treatment of a heartworm-infected animal), eperythrozoonosis, and haemobartonellosis. Minocycline and doxycycline are often effective to a somewhat lesser degree against resistant strains of S aureus. In addition to antimicrobial chemotherapy, the tetracyclines are used for other purposes. As additives in animal feeds, they serve as growth promoters. Because of the affinity of tetracyclines for bones, teeth, and necrotic tissue, they can be used to delineate tumors by fluorescence. Demethylchlortetracycline has been administered to inhibit the action of antidiuretic hormone in cases of excessive water retention. Because of either their metalloproteinase-inhibiting effects or their binding of calcium, they are used to stretch flexor digital tendons in neonatal foals. Finally, they are being used to decrease the risk of adverse events and to enhance killing of adult heartworms or microfilaria before adulticide treatment.
