Disposition of benzocaine in channel catfish

Abstract The concentration-time profile of total radioactivity and of unchanged benzocaine and each of its metabolites was characterized in male and female channel catfish ( Ictalurus punctatus ) after 25 °C water exposure of the fish to 70 mg 1 −1 (ppm) 14 C-benzocaine until anesthesia (about 5 min) and then to 35 mg 1 −1 for 30 min. The average concentration of radioactivity in the tissues and fluids ranged from 19.4 ± 14.3 ppm in white muscle to 143 ± 9.87 ppm in liver immediately after exposure. Concentrations of radioactivity in most tissues reached about 1% of the time 0 values by 25 h, and thereafter, the residue concentration-time profiles were loglinear up to 20 days; half lives were about 8 days except for 3.2 days in bile. At 10 days, the rank-order of residue concentrations was bile > liver > trunk kidney > head kidney > skin ≈ red muscle > plasma > white muscle. At 0 and 4 h post exposure, benzocaine was generally the dominant species in all tissues and fluids, and p -aminobenzoic acid was also observed. While gender differences were generally not detected, males showed higher concentrations of p -aminobenzoic acid and acetyl- p -aminobenzoic acid in bile than did females. Autoradiograms of whole-body sagittal sections showed bands of radioactivity concentration in the fibrous connective tissue (myosepta) that separate adjacent myomeres and attach to the vertebrae.