Distribution of oxytetracycline into ocular tissues and tears of calves.

A long-acting oxytetracycline formulation was administered (20 mg/kg of body weight) intramuscularly to calves, and the concentrations of the drug in serum, ocular tissues and tears were measured. The drug was distributed selectively to the epithelium of the conjunctiva and to the lacrimal gland ductules, and reached concentrations in each tissue that exceeded those in serum. The drug did not penetrate into the aqueous humour, and produced mean peak lacrimal fluid concentrations less than 1 microgram/ml after i.m. administration. When given subconjunctivally, however, concentrations greater than 2.0 micrograms/ml were observed in tears for 72 h. Severe local reactions occurred in all calves that were given the drug subconjunctivally.