Pharmacokinetic Studies of Lecithin Bound Iodine (LBI) in Rats (2): Absorption, Distribution and Excretion after Multiple Oral Administration.

Abstract

The absorption, distribution and excretion of [125I]lecithin bound iodine (LBI) were investigated in male rats after daily oral administration of 10 mg as iodine/kg for 7 days. 1. Concentration of iodine in the blood at 3 hr after daily dosing reached a steady state by the second dosing. At 24 hr after daily dosing, concentration of iodine was low and did not change with the number of doses. Concentration of iodine after the 7th dosing reached a maximum of 11.16 μg eq./ml at 1 hr and then declined with half lives of 6.7 and 23 hr at the observation periods of 3-12 hr and 24-72 hr, respectively. 2. At 24 hr after the 7th dosing, concentration of iodine in the thyroid gland was 415 times higher and those in the stomach, skin, fat, brown fat and bone marrow were 2-9 times higher, and those in the other tissues were similar to or lower than the concentration in the plasma. Elimination of iodine from tissues was comparably rapid. At 336 hr after the 7th dosing, concentration of iodine in the thyroid gland decreased to 66% of that found at 24 hr and those in the fat and epididymis were 37 and 33%, respectively, of those found at 24 hr. Concentrations in the other tissues were less than 22% of those found at 24 hr or below the detection limit. Whole body autoradiograms showed the similar distribution to the above findings. Distribution of iodine in blood cells was low, being about 33% and did not change with time. 3. Excretion ratios of iodine up to 24 hr after daily dosing in urine and feces were about 90 and 10% of the cumulative dose, respectively, and did not change with the increase in the number of doses. From the above findings, iodine in blood was specifically distributed to the thyroid gland al ready at 4 hr after dosing, and still remained markedly at 336 hr after dosing. The time course of iodine in the other tissues was parallel to that in the plasma, indicating no tendency to accumulate or remain.