DEPLETION OF THE RESIDUES OF COLISTIN AND AMOXICILLIN IN TURKEYS FOLLOWING SIMULTANEOUS SUBCUTANEOUS ADMINISTRATION

The tissue distribution and depletion of colistin and amoxicillin were studied in 84 turkeys dosed subcutaneously on 4 consecutive days with a formulation containing the two drugs at 0.2 ml/kg per day, correspo nding to 50 000 IU of colistin sulphate/kg and 20 mg of amoxicillin tr ihydrate/kg. All the turkeys were killed 1-30 days after the final dos e and samples of muscle, liver, kidney and cutaneous-subcutaneous tiss ues and of the injection site were taken for analysis for colistin and amoxicillin residues. The colistin concentrations in the liver (117.5 +/-26.0 ng/g) and cutaneous-subcutaneous tissue (100.0+/-35.6 ng/g) we re higher than those in kidney (92.0+/-34.4 ng/g) or muscle (67.5+/-16 .9 ng/g) 1 day after the final dose. The concentration of this drug th en increased for 9-14 days, followed by a slow decrease. The antibioti c was still present at low concentrations in the kidneys of all the tr eated birds and in the livers of two turkeys 30 days after the end of treatment. Amoxicillin concentrations were greatest in muscle (389.2+/ -195.0 ng/g) and at the injection sites (440.3+/-213.9 ng/g) 1 day aft er treatment ceased, with a subsequent rapid decline. This drug was un detectable in the livers and kidneys by 10 days after dosing ceased.