T. S. Atruktsang1, J. R. Imbus1, N. A. Zaborek1, D. F. Schneider1 1University Of Wisconsin,Department Of Surgery,Madison, WI, USA
Introduction:
Synthroid (levothyroxine) is one of the most prescribed drugs in the US. Despite its widespread use, and multiple dosing schemes, many patients struggle to achieve euthyroidism after thyroidectomy and suffer symptoms of hyper- or hypothyroidism. The purposes of this study are to describe time required for dose adjustment prior to achieving euthyroidism and to identify predictors of prolonged dose adjustment (PDA+) after thyroidectomy.
Methods:
This is a retrospective cohort study of patients from a single institution who achieved euthyroidism between 2007 and 2017 after undergoing total thyroidectomy or completion thyroidectomy for benign disease. Levothyroxine doses were calculated using our published BMI-based dosing algorithm; a single provider adjusted doses at 6 intervals. PDA+ was defined as needing at least 3 dose adjustments (top quartile) prior to achieving euthyroidism. We compared patient and disease characteristics of PDA+ patients to the remaining patients (PDA-) using Wilcoxon Rank Sum test or Chi-squared test where appropriate. Multivariate logistic regression was used to identify predictors of PDA+.
Results:
The 605 patients in this study achieved euthyroidism in a median of 116 days (range 14 – 863) and 1 dose adjustment (range 0 – 7). Only 222 (36.69%) patients were euthyroid without any dose adjustments. The 508 (83.97%) patients who were PDA- achieved euthyroidism in a median of 101 days (range 14 – 627) and 1 dose adjustment (range 0 – 2). The 97 (16.03 %) patients who were PDA+ achieved euthyroidism in a median of 271 days (range 52 – 863) and dose adjustments (range 3 – 7). PDA+ patients required more than twice the median number of days to achieve euthyroidism (271 vs. 101 days, p<0.001).
Compared to the PDA- group, the PDA+ group did not differ significantly in the proportion of patients with Graves’ disease or Hashimoto’s. However, PDA+ patients were more likely to have chronic renal insufficiency (5.2% vs. 1.6%, p=0.026). More than 3 times as many patients in the PDA+ group were taking iron (6.2% vs. 1.8%, p = 0.010). Similarly, nearly twice as many patients in the PDA+ group were taking multivitamin with minerals (22.7% vs. 11.6%, p = 0.003). When controlling for all other factors, iron supplementation (OR = 4.4, 95% C.I. = 1.43 – 13.55, p = 0.010) and multivitamin with mineral supplementation (OR = 2.4, 95% C.I. = 1.3 – 4.3, p = 0.004) were independently associated with PDA+. However, plain multivitamins were not associated with PDA+. Age, gender, preoperative thyroid disease, and co-morbidities did not independently predict PDA+.
Conclusion:
After thyroidectomy at a high-volume center, achieving euthyroidism can take nearly four months. Iron and mineral supplementation are associated with PDA+. This information can be useful when counseling patients preoperatively and suggests that education about proper levothyroxine administration and interfering supplements may expedite achieving euthyroidism.