The influence of age and body weight on levothyroxine replacement dosage to achieve euthyroidism in patients with primary hypothyroidism

Abstract

Introduction: Although, it is generally held that the levothyroxine (LT4) dose tends to decrease with age, this theory remains controversial. Our objective was to assess whether the LT4 dose required to achieve euthyroid status varies according to age, body weight (BW), sex, menopausal status, or antibody status.

Materials and methods: A cross-sectional study was performed from the retrospective review of the charts of patients with a previous diagnosis of primary hypothyroidism in treatment with LT4 and in a euthyroid state. Sex, age, actual body weight (ABW), TSH, and LT4 dose were recorded. Patients were grouped according to age ranges (18-44, 45-65, and over 65 years). A euthyroid state was defined as a serum TSH within the range of 0.4-4μIU/ml. A multiple linear regression model was performed to assess the LT4 dose and age, gender, antibody status, and ABW.

Results: A total of 882 charts of patients were reviewed. 586 patients met the inclusion criteria. The median age was 55 years. There was no correlation between the LT4 dose and age. A positive correlation was observed between the LT4 dose and ABW, but not with the ideal BW. Linear regression analysis showed that positivity antibody and ABW have a significant effect on the LT4 dose. Comparison of the LT4 dose between the different age groups showed no difference.

Conclusion: Our study demonstrates that the dose of LT4 necessary to achieve euthyroidism is influenced by ABW and the presence of antibodies. Age and menopause did not influence the required daily dose of LT4.

Keywords: Age; Edad; Euthyroidism; Eutiroidismo; Hipotiroidismo primario; Levothyroxine; Levotiroxina; Primary hypothyroidism.