Metabolism of Diiodosalicylic Acid in Dairy Calves

Diiodosalicylic acid (DIS) as a source of iodine has been investigated with dairy calves in three, seven-day balance trials involving four animals per trial. Two aninmls in each trial were dosed orally with I~-labelled diiodosa]icylic acid (DI~S) and two with I ~' 1 as iodide (I~-). Absorption from the gut, excretion patterns, thyroidal uptake, and the relationship of DIS sad plasma proteins were studied. Peak levels of radioactivity occurred in plasma approximately 24 hr post-dosing with DI~S, at which time over 90% of the activity was protein-bound. With I ~-, peak levels of activity occurred at approximately 8 to 10 hr, with less than 1% of the activity being protein-bound. Urinary excretion of activity averaged 83.2 and 46.1% (P < 0.01) and fecal excretion averaged 6.4 and 20.0% (P < 0.01) of the dose with DI~s~S and I ~=-, respectively. Although fecal excretion of activity from DI~S was significantly lower, total excretion was greater (P < 0.01). Thyroid uptake of 11~1 in four calves dosed with DI~=S (two iv and two oral) averaged 5.5%, compared to 26.8% in two calves dosed orally with I ~-.