Efficacy of a levothyroxine dosage regimen based on serum thyrotropin level, for primary hypothyroidism. An open...

There are no guidelines on individualized initial levothyroxine dosage in primary hypothyroidism. This prospective observational study was done to assess whether a predetermined dose of levothyroxine based on Thyroid Stimulating Hormone (TSH) levels would be able to make the patient euthyroid during a period of six weeks and to find other factors which influence the levothyroxine requirement.

Newly diagnosed patients with primary hypothyroidism or those patients who were not on levothyroxine therapy were divided into TSH-based groups-Group 1, 5-9.99, Group 2, 10-29.99, Group 3, 30-99.99 and Group 4, >100 μIU/ml and treated with an initial levothyroxine dose of 25,50,75 and100 μg/day for next six weeks. Factors correlating with levothyroxine requirement were determined.

Of the 171 patients who were included 142 completed the study, 34,46,28 and 34 patients were included in groups 1 to 4, respectively. Normalization of TSH with the above criteria was achieved in 111 (78.7%) out of 141 patients, and 91%, 67%, 75%, and 82% respectively in the 4 groups. Among adequately replaced patients pre-treatment TSH level (r = 0.81), T4 level (r = 0.61), and body weight (r = 0.19) correlated with the levothyroxine requirement. Based on these factors predicted initial dose (μg/day) was found to be 0.54 (Body Weight [Kg]) +0.47 (TSH [μIU/m]) - 1.4 (Total T4 [μg/dl]) +17.79 or 0.27 (Body Weight) +0.553 (TSH) +21.

Serum thyrotropin-based categorization for initial levothyroxine dose leads to euthyroidism in nearly four of five patients with primary hypothyroidism. The dose required for adequate replacement of levothyroxine has correlation with pre-treatment serum TSH levels serum thyroxine levels and body weight.