Abstract
Pharmacokinetics of sulfadimethoxine (SDMX) in skin of broiler chicken after intravenous and in-drinking-water administrations were investigated to examine the reason for a longer residue of SDMX in the skin which was observed in the residue study after administration via drinking water at a concentration of 1, 000 ppm. The decay curve of SDMX in the skin after single intravenous injection of 200 mg/kg, the highest dose, was fitted to the two compartment model with T1/2 of 4.4 hrs in the first elimination phase and 173 hrs in the second one. The extrapolated concentrations in the skin at 24 hrs after the injection were calculated to be 69.0 μg/g for the 1st phase and 0.11 μg/g for the 2nd phase. The decay curves in the skin after single injection of 30 and 100 mg/kg were fitted to the one compartment model with T6lt;1/2> of 3.2 and 5.7 hrs, respectively. Dividing a high dose into 3 to 5 doses and injecting sequentially with intervals of the previously measured T1/2, SDMX concentrations in the skin were about half of those in the plasma and ran parallel. The plasma concentration-time curves after single intravenous injection of SDMX more than 100 mg/kg showed nonlinear kinetics with concentrations over 100 μg/ml for 12-30 hrs after the injection. By administration of SDMX via drinking water, a sustained residue curve of SDMX in the skin at 1, 000 ppm reported previously was not observed at 500 ppm. These results suggest that existence of two compartments for SDMX in the skin, i.e. the concentration in the first compartment ran parallel with that in plasma and only a slight portion of plasma SDMX was uptaken by the second compartment to be eliminated extremely slowly.
