Kinetics of a Single Administration of 74Se‐Selenite by Oral and Intravenous Routes in Adult Humans

The purpose of this study was to explore the fate of a single dose of labeled selenium as determined by its route of administration. Thus, the appearance of a stable isotope of selenium, administered as 74‐Se‐selenite, was measured in plasma, urine, and feces, with neutron activation analysis, following a 81.7 μg dose of 74Se‐selenite given either intravenously or orally in two groups (n = 4) of healthy, young adult men, who were otherwise maintained on a diet providing a constant and adequate selenium intake. From these isotopic data, measurable parameters of urine excretion, total body retention and selenite‐exchangeable metabolic pool (Se‐EMP) were defined to provide a quantitative assessment of selenium metabolism in these subjects. The initial 24‐hr urine excretion of the label was higher for the intravenously administered label (18.2 ± 2.1% of dose) compared to the oral dose (11.7 ± 2.6% absorbed dose). Thereafter, the excretion of isotope was the same for both groups. For equivalent entry of Se into the body, measured total body retention and Se‐EMP were the same for both groups. These initial kinetic data suggest that the overall utilization of selenium from a single administration of selenite is comparable for the two routes of intake and that the host's selenium requirement can probably be met adequately via the intravenous administration of selenite. (Journal of Parenteral and Enteral Nutrition 12:351–355, 1988)