Irreversible in vivo binding of thiabendazole to macromolecules in pregnant mice and its relation to teratogenicity

The binding of [14C]thiabendazole ([14C]TBZ) to macromolecules in the liver, foetus and other tissues was investigated in Jcl:ICR mice on day 13 of gestation. TBZ suspended in olive oil was given orally in a dose of 1 g/kg body weight (5 microCi/mouse) and the mice (in groups of three) were killed 0.5, 1, 3, 6, 24 and 96 hr later. The bound radioactivity in the liver and foetus was at a maximum between 3 and 24 hr after treatment. The rate of decrease of the bound radioactivity was slower than that of total radioactivity. Bound radioactivity was also present in other tissues (including kidney, lung, heart, placenta and spleen). The level of bound radioactivity was measured in the liver and foetuses after oral administration of teratogenic doses of 200-1600 mg/kg. Disproportionate increases in bound radioactivity were observed in both tissues after administration of the highest dose.