Inhalation toxicokinetics of butoxyethanol and its metabolite butoxyacetic acid in the male Sprague-Dawley rat

A total of 16 male Sprague-Dawley rats were continuously exposed to 20 ppm or 100 ppm butoxyethanol (BE) vapor for 1, 2, 3, 4, 6, 8, 10, or 12 days. Urine was collected in 24-h intervals and stored at -70 degrees C. At the end of the exposure the animals were euthanized by decapitation and tissue samples of blood, muscle, liver and were rapidly collected and frozen to -70 degrees C. The samples were later derivatized and analyzed for BE and its major metabolite butoxyacetic acid (BAA) by electron capture gas chromatography. BE and BAA were rapidly distributed to the tissues examined. The concentration of BE in blood was slightly higher, and that of BAA markedly higher than in other tissues, indicating weak (BE) and pronounced (BAA) blood protein binding, respectively. BE was efficiently metabolized and the blood clearance averaged 2.6 l/h per kg, corresponding to a hepatic extraction ratio of about 0.75. The renal clearance of BAA (average 0.53 l/h per kg) corresponded to approximately 15% of the renal blood flow. The kinetics of BE and BAA were linear up to 100 ppm. There were no clear indications of changes in the toxicokinetics, such as metabolic induction or inhibition of metabolism or excretion, during the course of the exposure. The recovery of BAA in urine was 64% of the calculated inhaled amount of BE, on an equimolar basis.