DEPLETION AND BIOAVAILABILITY OF [C-14] FURAZOLIDONE RESIDUES IN SWINE TISSUES

Six swine (three male, three female) were dosed orally with [C-14]furazolidone for 14 days at a dose level of 16.5 mg kg(-1) day(-1). At 0-day (10-h) withdrawal, liver contained' the highest residues (41.1 ppm) followed by kidney (34.4), muscle (13.2), and fat (6.2). After a 45-day withdrawal, all tissues had total residues of approximately 2.0 ppm. The amount of aminooxazolidinone (AOZ) released from the bound tissue residues, on average, represented 7.5% of the total residues. Additional tissue samples were lyophilized, pelleted, and fed to rats for determination of bound residue bioavailability using the Gallo-Torres model. Bioavailability of Liver residues decreased from 40% at 0-day withdrawal to 19% after 45 days, while muscle residues showed no change in relative bioavailability with corresponding values of 37% and 41%. Pretreatment of tissue samples with organic solvents to generate a nonextractable pellet removed 10-20% of the initial radioactivity but had no effect on the overall bioavailability of the remaining residues.