Tissue sulfonamide concentration and correlation in turkeys

Nineteen hen turkeys (10 to 12 kg each) were used in a feeding study to determine sulfadimethoxine and sulfaquinoxaline concentrations in blood serum, liver, and skeletal muscle, as well as the respective ratios at selected withdrawal intervals. Two feeds were prepared by use of premixes to achieve 60 mg of sulfadimethoxine/kg and 100 mg of sulfaquinoxaline/kg, respectively. Each of the medicated feeds was given to 9 turkeys for 7 days. The turkeys were then fed nonmedicated feed at intervals from 24 to 56 hours and were slaughtered. One turkey was used as control. The serum/liver and serum/muscle ratios for sulfaquinoxaline were 60 to 70% higher than for sulfadimethoxine. However, the liver/muscle ratio for both sulfonamides was equivalent, approximately 3. Disposition of both sulfonamides approximated first-order pharmacokinetics. The calculated half-life of sulfadimethoxine was half that of sulfaquinoxaline, approximately 16 vs 30 hours. The coefficients of variation in the serum/tissue ratios for both sulfonamides were between 13% and 25% for serum/liver and less than 15% for serum/muscle, indicating excellent potential for using serum as a predictor of actionable concentrations of sulfonamide residues.