Profile of Levothyroxine Replacement Therapy in Graves’ Disease Patients with Hypothyroidism Post-Radioactive Iodine Ablation: Focus on Different Weight-Based Regimens

Abstract

Objective

To evaluate the status of euthyroidism achieved among Thai patients with post-ablative hypothyroidism and to examine the difference between various weight-based daily levothyroxine (LT4) replacement regimens in these patients.

Methodology

We conducted a retrospective review of Thai patients with Graves’ disease (GD) who developed hypothyroidism following radioactive iodine treatment from 2016 to 2020 at Theptarin hospital. Daily LT4 dose was calculated based on actual body weight (ABW), ideal body weight (IBW), and estimated lean body mass (LBM).

Results

We reviewed a total of 271 patient records. Of these, 81.2% were females with a mean age of 40.8±11.7 years, LT4 intake duration of 27.1±14.6 months, and LT4 dose/kg ABW of 1.4±0.5 μg/kg/day. At the final follow-up, 62.4% of patients achieved thyroid-stimulating hormone (TSH) levels within the reference interval, 15.5% had TSH levels over, and 22.1% had TSH levels under the reference range. Obese patients required a lower daily LT4 dose relative to ABW and higher daily LT4 dose relative to IBW to attain euthyroidism (ABW 1.1±0.4 μg/kg/day and IBW 2.0±0.8 μg/kg/day). Estimated daily LT4 dose based on LBM showed a constant dosage of 2.0 μg/kg/day in all BMI categories.

Conclusions

Suboptimum LT4 replacement therapy was found in almost half of hypothyroid patients with GD treated with radioactive iodine. Estimated LBM was a better indicator for dosing calculation in these patients compared with ABW and IBW.