[Doxycycline hydrochloride administered in the drinking water to poultry]

Investigated were the acute toxicity, serum concentrations, and residual amounts of doxycycline in broiler chickens. It was found that the LD50 of doxycycline when applied via the crop to week-old broiler birds was 2500 mg/kg mass. The amount of 0.005 g/kg mass given orally to birds led to serum concentrations that on the eighteenth hour were found to drop up to subtherapeutic ones. When applied with the drinking water at the rate of 0.02 to 0.04 g l or kg feed it was well absorbed as early as the first hours. In such case the drug maintained therapeutic concentrations that were higher in the internal organs than those in the serum. The residual amounts of doxicycline hydrochloride when it was applied at 0.04 g/l of water or kg feed were found up to 48 h hour by the method of agar diffusion, using Bac. subtilis L2 as a test organism. The withdrawal time should amount to 72 hours.