AIM: To evaluate the relative bioavailibility and bioequivalence of new and old imported
levothyroxine sodium tablets in
Chinese healthy sub-jects. METHODS: The study was performed in 24 healthy male volunteers according to a randomized 2-way crossover design with a washout period of 35 d. The blood samples were collected at 30,15,<4 min before and 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 6.0, 8.0, 10.0, 12.0, 18.0, 24.0, 48.0 h after taking 600 μg of two kinds of
levothyroxine sodium tablets. The concentrations of serum total T 4 and T 3 were determined by
radioimmunoassay. RESULTS: The serum T 4 concentration showed obvious changes with time following administration of two kinds of tablets.The pharmacokinetic parameters for the new and old tablets were as follows:(3.4±s 2.3) and (3.5± 2.1) h for t max, (168±39) and (160±34) μg·L -1 for c max, (5 640±1 060)and (5 620± 1 010) μg·h·L -1 for AUC 0-48, respectively. However, the serum T 3 concentration did not change significantly after administration of both kinds of tablets. CONCLUSION: The relative bioavailability of new levothyroxine sodium tablet is (102±18) %. The new and old levothyroxine sodium tablets are bioequivalent.