Management of overt and subclinical hypothyroidism: factors influencing L-thyroxine dosage

With the aim of establishing optimal dosage schedules, 171 women with either orvet (OH, n=80) or subclinical (SCH, n=91) hypothyroidism were assessed before and 6 months after starting L-thyroxine (LT4) replacement therapy. Each group was further classified into four subgroups according to post-therapy serum TSH level, as follows; A) complete suppression; B) partial suppression; C) normal range and D) above normal range (insufficient response). In all subgroups, LT4 doses were higher for OH than for SCH, whether expressed as total daily dose (mug) or as a function of either actual or ideal body weight (mug/kg BW). In OH, LT4 dose was higher for subgroups A or B as compared with either C or D. In SCH, subgroup A received a larger dose than the other subgroups. Post-treatment serum thyroxine levels showed the same pattern for both OH and SCH. Mean LT4 dose was similar in patients with high and normal antithyroid antibodies and in patients with goiter and in those without it. In goitrous patients thyroid volume decreased in subgroup B, particularly in those patients that had elevated antithyroid antibodies, but not in subgroup C. In OH patients a significant negative correlation was found between daily LT4 dose per Kg actual BW and actual BW, especially in subgroup C for patients with a body mass index > 27 kg/cm2 (r = -0.90, p<0.001). In subgroup C of the SCH group, a negative correlation between LT4 dose and age was noticed. Both in OH and in SCH, LT4 dose per kg actual BW required to obtain a serum TSH within the normal range was lower in women with a body mass index (BM) > 27 kg/m2 than in those with a BMI = 27 kg/m2. LT4 doses for subgroup C did not differ from those needed in hypothyroid patients with previous Graves disease, in either OH or SCH patients. (AU)