Vitamin Absorption Studies

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Abstract
Normal male subjects, receiving nutritionally adequate diets, were given oral doses of one to 20 mg of thiamine and riboflavin and the urinary excretion of the vitamins was determined until excretion levels returned to those found prior to dosing. The excretion of thiamine, expressed as percentage of dose, decreased markedly with doses greater than 2.5 mg. Increasing the dose from 2.5 to 20 mg increased the amount of thiamine excreted by only 0.2 mg. In contrast, riboflavin excretion remained a constant percentage of dose. Excretion of thiamine after a 10-mg dose was increased threefold by giving the vitamin in 4 doses of 2.5 mg each, at two-hour intervals. Preparations designed to produce sustained release of thiamine in a single dosage form were found to vary markedly in availability and showed no evidence of sustained-release properties. Administration of riboflavin in divided doses produced sustained urinary excretion of the vitamin, but had no significant effect on the total amount of riboflavin excreted.