Thyroid uptake of 131I: further comparisons of capsules and liquid preparations

Comparisons were made of thyroid uptake of three commercially available preparations of 131I, using a double-blind design, in 125 patients with normal thyroid function. Uptakes with Squibb Iodotope Diagnostic capsules were significantly lower than those with Squibb Iodotope Oral liquid at 4 hr (p less than 0.01) and 24 hr (p less than 0.05) after ingestion in both the general population and in all patients less than 45 years of age. Uptakes of Radiocaps I-131 (Abbott Laboratories) and Iodotope Oral liquid were indistinguishable under identical conditions. Our findings indicate that interference with either absorption or metabolism of a pharmaceutical can result from the vehicle used to administer it.