Body Weight as a Major Determinant Section of Thyroxine Sodium Dosage in the Treatment of Primary Hypothyroidism

Introduction: Several formulae have been proposed for optimising the dosage prerequisites of levothyroxine (LT4), and body weight and Body Mass Index (BMI) have been suggested to be broadly dependent on the formulae range.

Aim: To evaluate the role of body weight as a determinant of LT4 dosage in the treatment of primary hypothyroidism.

Materials and Methods: The present study was a prospective observational study conducted at Outpatient Department (OPD) Endocrinology, Patna Medical College Hospital, Patna, Bihar, India, on 100 patients diagnosed with untreated primary hypothyroidism between February 2020 and January 2021. Demographic details, anthropometric measurements, vital signs, and details of types and dosage of treatment received were collected. LT4 dose requirement for each individual patient was then generated as mcg per kg/body weight per day. Estimation of serum Thyroid Stimulating Hormone (TSH), Free T4 (FT4), creatinine and thyroid peroxidase levels were carried out as per standard diagnostic protocols and the dosage adjustment was conducted based on target TSH levels. Population characteristics were expressed as mean±standard deviation. The Python version 3.4.5 with the package seaborn was used for statistical analyses and preparation of figures, distribution and correlation plots.

Results: The study enrolled 100 individuals (88 women and 12 men) with mean age of 40.69 years (age range 17 to 72 years). A significant positive correlation was noted between the LT4 dose and total body weight (p-value <0.001). The association was also significant when the LT4 dose was correlated with BMI (p-value <0.001) and FT4 (p-value <0.001). However, the correlation of Thyroid Peroxidase Antibodies (TPO Ab), TSH, height and age with the LT4 daily dose (p-value >0.05) was found to be statistically non significant.

Conclusion: There exist a significant positive correlation between LT4 dosage and body weight. Hence, body weight should be considered as a key determinant while prescribing LT4 therapy for the treatment primary hypothyroidism.