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Ann Med Interne (Paris). 1983;134(7):636-42.

[Posologic equivalents of oral L-thyroxine in thyroid insufficiency (120 cases)].

[Article in French]
[No authors listed]

Abstract

The effects of two successive courses of thyroid replacement therapy in the same patients can be compared by measuring plasma hormone levels at the steady state. This method was used to assess the effects of the two forms of oral L-thyroxine, the one in liquid drops 5 micrograms/drop and the other in 50 and 100 micrograms tablets, and to compare these preparations with other forms of thyroid replacement therapy: DL T4, LT3 + LT4 and thyroid extract. The bioequivalence of these drugs was determined by the logarithmic difference of the plasma TSH during successive treatment periods. In addition, this factor could be assessed by the ratios of circulating T4 to T3 when the two treatment periods were identical. One 100 micrograms tablet of L-thyroxine was equivalent to 20 drops of L-thyroxine (100 micrograms), i.e. the bioavailability of the two preparations was identical. This dose was equivalent to three drops of DL thyroxine (i.e. 100 micrograms of L-thyroxine): the D-thyroxine did not have any demonstrable hormonal properties. The same dose was equivalent to about 3/4 of a tablet of LT3 + LT4, and to about 12 cg of thyroid extract. Individual stabilisation with L-thyroxine in cases of peripheral thyroid deficiency was based on basal TSH levels and TSH levels after injection of TRH when the basal TSH was normalised. The plasma T3 and T4 levels could also be used for optimal equilibrium with L-thyroxine; the first should be within the normal range and the second in the normal or mildly hyperthyroid range. The optimal adult dose of L-thyroxine in this study was variable (115 +/- 40 micrograms/day). In young children, especially babies, the effective dose with respect to body weight, is much greater.

PMID:
6666901
[Indexed for MEDLINE]
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