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, corresponding to 50 000 IU of colistin sulphate/kg and 20 mg of amoxicillin trihydrate/kg. All the turkeys were killed 1-30 days after the final dose and samples of muscle, liver, kidney and cutaneous-subcutaneous tissues 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) were 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 then increased for 9-14 days, followed by a slow decrease. The antibiotic was still present at low concentrations in the kidneys of all the treated 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 after treatment ceased, with a subsequent rapid decline. This drug was undetectable in the livers and kidneys by 10 days after dosing ceased.