Comparison of the effect of a single oral L-thyroxine dose (150 micrograms) in tablet and in solution on serum thyroxine and TSH concentrations.

150 micrograms of L-thyroxine were administered to each of 14 euthyroid goitrous patients orally between 7:30 and 8:30 a.m. after fasting overnight. The L-T4 dose given was one and half tablets of the drug "Eutirox" (L-T4 tablet of 100 micrograms distributed by Bracco, Milan, Italy) or one and half ml of the solution "Tiroxen" (solution containing 100 micrograms/ml of L-T4 distributed by Laboratori Baldacci, Pisa, Italy). Two studies (one with tablet and one with solution) were performed on each patient. The tablet or the liquid form of L-T4 were administered in random order. In each study a blood sample for serum hormone determination was drawn immediately before L-T4 administration, then 30 minutes later and every hour up to the fifth hour after. The second study was performed in similar fashion later. The mean serum TT4 concentration value at any time was very similar in the two studies, thus showing the same time course after the administration of solution and the tablet formulation. The mean basal TT4 value (9.07 +/- 0.56 and 8.90 +/- 0.73 micrograms/dl respectively) increased significantly at the first and second hours. The highest value was reached at the second and at the third hour after the solution (11.15 +/- 0.58 micrograms/dl) and the tablet (11.81 +/- 0.78 micrograms/dl) respectively. Subsequently, the mean TT4 values remained significantly higher than basally over the entire 5 hours. The FT4 mean serum concentration at all times were very similar in the two studies and showed the same time course.(ABSTRACT TRUNCATED AT 250 WORDS)