Long term therapy with a new liquid L-thyroxine preparation: bioequivalence with L-T4 tablets

Seventy-four euthyroid patients with nodular goiter (55) or primary hypothyroidism (19) were selected for long term treatment with a new preparation containing L-T4 in solution (Tiroxen, Laboratori Baldacci, Pisa, Italy). Each patient underwent, before or after receiving the L-T4 in solution, long term treatment with L-T4 in tablet form at the same dose. The serum concentrations of TSH, TT4, TT3, FT4 and FT3 were measured basally and during therapy with each of the two L-T4 preparations (liquid and tablet). In the golter group, mean serum TSH concentration was 1.4 microUI/ml basally, while it was 0.47 microUI/ml following both L-T4 tablet therapy and L-T4 solution administration. Mean basal TSH value was significantly different from the two values on the therapy (p < 0.001 in each instance). Mean basal serum TT4 concentration was 8.2 +/- 0.25 microgram/dl basally while it was 9.9 +/- 0.28 microgram/dl (p < 0.001) on L-T4 tablet therapy and 9.7 +/- 0.26 (p < 0.001) on L-T4 solution administration. Mean basal serum concentration of TT3, FT4, FT3 was not significantly different from the value on the therapy, either with L-T4 tablet or with L-T4 solution. In the hypothyroid patients the high mean basal serum TSH concentration (23.6 microUI/ml) returned to normal similar values on L-T4 tablet therapy (0.96 microUI/ml; p < 0.01) and on L-T4 solution administration (1.24 microUI/ml; p < 0.01). The serum TSH concentration value during L-T4 therapy varied from unmeasurable level to 3.5 microUI/ml during the tablet administration and to 4.8 microUI/ml during the solution administration.(ABSTRACT TRUNCATED AT 250 WORDS)