Evaluation of Thyroid Hormone Replacement Dosing in Overweight and Obese Patients After a Thyroidectomy

The pharmacist's role in optimizing medication management before, during, and after minimally invasive and bariatric surgery

PURPOSE

Minimally invasive surgery (MIS) with integrated enhanced recovery pathways (ERPs) helps reduce length of stay and improve surgical outcomes. As these procedures have become more prevalent over time, pharmacists are in key positions to manage medications in the perioperative space to help optimize transitions of care and reduce safety events. Here we identify several clinical areas across phases of care for these procedures in which the knowledge and guidance of pharmacists, as members of the interprofessional team, are paramount.

SUMMARY

Perioperative pharmacy expertise is often required for MIS procedures in the areas of acid suppression, antithrombotic management, blood glucose control, drug formulation, immunosuppressant optimization, pain mitigation, and postoperative nausea and vomiting prevention and treatment. For each MIS procedure, pharmacists should identify and consider diet and anatomical changes as well as patient- and surgery-specific risk factors. Pharmacists can then utilize their knowledge of the pharmacokinetics and pharmacodynamics of individual medications along with evidence-based medicine to recommend selection of appropriate agents.

CONCLUSION

Pharmacist contributions to perioperative medication management for MIS procedures can improve care as surgical patients navigate transitions through the perioperative setting. Pharmacists can further incorporate medication expertise through development and implementation of institutional MIS protocols within the context of ERPs. As such, any pharmacist should feel empowered to aid in the care of surgical patients.

Analysis of factors influencing the dose of levothyroxine treatment in adequately controlled hypothyroid patients of different etiologies

Objective

The mainstay therapy of hypothyroidism is levothyroxine (LT4). In most cases lifelong treatment is warranted, therefore, choosing adequate doses are of paramount significance. The purpose of this study was to assess several factors that have been proposed to influence LT4 therapy including etiology of hypothyroidism, gender, age, bodyweight, BMI, concomitant drug use, disease severity and time since diagnosis in patients with stable, adequately controlled hypothyroidism.

Methods

In this cross-sectional study we analysed past medical history, anthropometric data and biochemical parameters reflecting thyroid function of patients with chronic hypothyroidism who were adequately treated (TSH levels in normal range) with LT4 for at least 6 months. Potential predictors of LT4 requirement were evaluated using uni- and multivariate linear modelling.

Results

191 individuals were enrolled in this study, who were divided into autoimmune (n = 147) and post-surgery (n = 44) groups. Mean age, time since diagnosis and LT4 dose (1.3 versus 1.1 mcg/kgBW) were significantly lower in the autoimmune group. In the post-surgery group age was the only significant (p = 0.016) predictor of LT4 dose. In the autoimmune group BMI (p = 0.001), time since diagnosis (p = 0.023), as well as their interaction (p = 0.012) turned out to be significant predictors of LT4 requirement.

Conclusions

Our results implicate the necessity of differentiating between etiologies of hypothyroidism when starting or changing thyroxine replacement therapy. Patient in both groups required significantly lower doses of LT4 replacement, than previous reports suggest, to maintain stable euthyroidism. Distinctly different factors predicted hormone requirement in the two study groups.

Adequate Dose of Levothyroxine for Thyroid-Stimulating Hormone Suppression after Total Thyroidectomy in Patients with Differentiated Thyroid Cancer

BACKGRUOUND

The adequate dose of levothyroxine (LT4) for patients who have undergone total thyroidectomy (TT) for differentiated thyroid cancer (DTC) is uncertain. We evaluated the LT4 dose required to achieve mild thyroid-stimulating hormone (TSH) suppression in DTC patients after TT.

METHODS

The electronic medical records of patients who underwent TT for DTC and received mild TSH suppression therapy were reviewed. Linear regression analysis was performed to evaluate the association between LT4 dose (μg/kg) and an ordinal group divided by body mass index (BMI). We also evaluated the trend in LT4 doses among groups divided by BMI and age.

RESULTS

In total, 123 patients achieved mild TSH suppression (0.1 to 0.5 mIU/L). The BMI variable was divided into three categories: <23 kg/m2 (n=46), ≥23 and <25 kg/m2 (n=30), and ≥25 kg/m2 (n=47). In the linear regression analysis, BMI was negatively associated with the LT4 dose after adjusting for age and sex (P<0.001). The LT4 doses required to achieve mild TSH suppression based on the BMI categories were 1.86, 1.71, and 1.71 μg/kg, respectively (P for trend <0.001). Further analysis with groups divided by age and BMI revealed that a higher BMI was related to a lower LT4 dose, especially in younger patients aged 20 to 39 (P for trend=0.011).

CONCLUSION

The study results suggest an appropriate LT4 dose for mild TSH suppression after TT based on body weight in patients with DTC. Considering body weight, BMI, and age in estimating LT4 doses might help to achieve the target TSH level promptly.

Obesity and Obesity-Related Thyroid Dysfunction: Any Potential Role for the Very Low-Calorie Ketogenic Diet (VLCKD)?

PURPOSE OF REVIEW

This review aims to explore in-depth the different aspects of the association between very low-calorie ketogenic diet (VLCKD), obesity and obesity-related thyroid dysfunction.

RECENT FINDINGS

The VLCKD, proposed as a non-pharmacological strategy for the management of certain chronic diseases, is becoming increasingly popular worldwide. Initially used to treat epilepsy, it has been shown to be effective in controlling body weight gain and addressing various pathophysiological conditions. Research has shown that a low-calorie, high-fat diet can affect thyroid hormone levels. Weight loss can also influence thyroid hormone levels. Studies have suggested that long-term use of VLCKD for refractory epilepsy may be related to the development of hypothyroidism, with an effect seen in various populations. In particular, women with obesity following VLCKD tend to have reduced T3 levels. We propose further research to unravel the underlying mechanisms linking VLCKD to obesity and obesity-related thyroid dysfunction.

Optimizing Thyroxine Dosage After Total Thyroidectomy: Understanding the Factors at Play

INTRODUCTION

Total thyroidectomy is evolving as the choice of treatment for non-malignant thyroid conditions. Therefore, an ideal method of thyroxine replacement is necessary to avoid the ill effects of under- and over-replacement in such patients.

AIM

To assess the correlation between optimal thyroxine dose and potential variables like lean body mass (LBM), body surface area (BSA), body mass index (BMI), body weight, age, and sex in patients who underwent total thyroidectomies for benign multinodular goiters in our institute.

MATERIALS AND METHODS

A longitudinal cohort study was undertaken at the Government Medical College Thrissur, a tertiary care provider in India, between October 2018 and September 2019. One hundred adult patients who underwent a total thyroidectomy for various benign thyroid conditions were included. They were initially given thyroxine 75 µg upon discharge and received follow-up doses every two months until they achieved euthyroid status on two consecutive visits. The variables evaluated at this stage included age, sex, actual body weight, lean body weight, BMI, and biochemical data (triiodothyronine (T3), thyroxine (T4), thyroid-stimulating hormone (TSH)). Correlation, multiple step-wise regression, and variance were carried out using EPI INFO version 7.2.2.6.

RESULTS

The best predictors for optimum thyroxine dose were BSA (0.923, P < 0.01) and LBM (0.921, P < 0.01), compared with body weight (0.833, P < 0.01) and BMI (0.523, P < 0.01). In our study, the least significant factor was the age of the patient (r = 0.117, P < 0.01). There was no significant association between gender and thyroxine dose. The mean thyroxine dose was 1.87 µg/kg of the patient's body weight.

CONCLUSION

The optimum thyroxine replacement based on BSA or LBM is a more ideal method than based on BMI or body weight alone.

Recurrent Graves' Disease Following Near-Total Thyroidectomy: A Case Report and Literature Review

Recurrent Graves' disease due to regrowth of thyroid tissue is a rare complication of near-total thyroidectomy, which can be challenging to recognize and manage. Here, we present the case of a 30-year-old woman with Graves' disease and thyroid eye disease who underwent near-total thyroidectomy with resultant hypothyroidism. Her levothyroxine dose requirement gradually decreased and thyroglobulin level increased, which led to the diagnosis of recurrent Graves' disease. A neck ultrasound showed regrowth of thyroid tissue. The treatment options in such cases are repeat thyroid surgery and radioactive iodine ablation. The patient had moderate-severe active thyroid eye disease, so radioactive iodine ablation was contraindicated. Repeat surgery was deemed high risk due to the location of the residual thyroid tissue near the recurrent laryngeal nerve. Watchful waiting with serial thyrotropin (TSH) receptor antibody monitoring was chosen, and her levothyroxine dose was adjusted based on her thyroid function tests. There was a normalization of her TSH receptor antibody level over the next two and half years and stabilization of levothyroxine dose requirement. Recurrent Graves' disease must be considered when there is an ongoing decrease in the levothyroxine dose requirement associated with a rise in the serum thyroglobulin level following near-total thyroidectomy. Conservative management with medical therapy can induce remission in the case of recurrent Graves' disease following near-total thyroidectomy, without the need for radioactive iodine ablation or repeat thyroid surgery.

Subclinical Hypothyroidism in Patients with Obesity and Metabolic Syndrome: A Narrative Review

The literature on the connection between obesity, metabolic syndrome, and subclinical hypothyroidism is critically analyzed in this narrative review. These conditions are frequently observed among adult populations and various studies and meta-analyses have assessed their association. The prevalence of subclinical hypothyroidism in obese individuals is higher than in non-obese subjects and this trend is more pronounced in unhealthy obesity phenotypes. However, the diagnosis and treatment of subclinical hypothyroidism can be difficult in obese patients. Exaggerated body fat is linked to thyroid hypoechogenicity as evident through ultrasonography and euthyroid obese people have greater TSH, FT3, and FT3/FT4 ratios than non-obese individuals in a euthyroid condition. Moreover, a reduced expression of the TSH receptor and altered function of deiodinases has been found in the adipose tissue of obese patients. Current data do not support the necessity of a pharmacological correction of the isolated hyperthyrotropinemia in euthyroid obese patients because treatment with thyroid hormone does not significantly improve weight loss and the increase in serum TSH can be reversible after hypocaloric diet or bariatric surgery. On the other hand, obesity is linked to elevated leptin levels. Inflammation can raise the risk of Hashimoto thyroiditis, which increases the likelihood that obese patients will experience overt or subclinical hypothyroidism. Both metabolic syndrome and subclinical hypothyroidism are associated with atherosclerosis, liver and kidney disease. Hence, the association of these two illnesses may potentiate the adverse effects noted in each of them. Subclinical hypothyroidism should be identified in patients with obesity and treated with appropriate doses of L-thyroxine according to the lean body mass and body weight. Randomized controlled trials are necessary to verify whether treatment of thyroid deficiency could counteract the expected risks.

Computer-Assisted Levothyroxine Dose Selection for the Treatment of Postoperative Hypothyroidism

Background: Thyroid hormone replacement with levothyroxine (LT4) is a recommended treatment for patients undergoing thyroidectomy. The starting LT4 dose is frequently calculated based on the patient's weight. However, the weight-based LT4 dosing performs poorly in clinical practice, with only ∼30% of patients achieving target thyrotropin (TSH) levels at the first thyroid function testing after treatment initiation. A better way to calculate the LT4 dose for patients with postoperative hypothyroidism is needed. Methods: In this retrospective cohort study we used demographic, clinical, and laboratory data for 951 patients after thyroidectomy and several regression and classification machine learning methods to develop an LT4 dose calculator for treating postoperative hypothyroidism targeting the desired TSH level. We compared the accuracy with the current standard-of-care practice and other published algorithms and evaluated generalizability with fivefold cross-validation and out-of-sample testing. Results: The retrospective clinical chart review showed that only 285/951 (30%) patients met their postoperative TSH goal. Obese patients were overtreated with LT4. An ordinary least squares regression based on weight, height, age, sex, calcium supplementation, and height:sex interaction predicted prescribed LT4 dose in 43.5% of all patients and 45.3% of patients with normal postoperative TSH (0.45-4.5 mIU/L). The ordinal logistic regression, artificial neural networks regression/classification, and random forest methods achieved comparable performance. LT4 calculator recommended lower LT4 doses to obese patients. Conclusions: The standard-of-care LT4 dosing does not achieve the target TSH in most thyroidectomy patients. Computer-assisted LT4 dose calculation performs better by considering multiple relevant patient characteristics and providing personalized and equitable care to patients with postoperative hypothyroidism. Prospective validation of LT4 calculator performance in patients with various TSH goals is needed.

Efficacy of machine learning to identify clinical factors influencing levothyroxine dosage after total thyroidectomy

BACKGROUND

We employed Machine Learning (ML) to evaluate potential additional clinical factors influencing replacement dosage requirements of levothyroxine.

METHOD

This was a retrospective study of patients who underwent total or completion thyroidectomy with benign pathology. Patients who achieved an euthyroid state were included in three different ML models.

RESULTS

Of the 487 patients included, mean age was 54.1 ± 14.1 years, 86.0% were females, 39.0% were White, 53.0% Black, 2.7% Hispanic, 1.4% Asian, and 3.9% Other. The Extreme Gradient Boosting (XGBoost) model achieved the highest accuracy at 61.0% in predicting adequate dosage compared to 47.0% based on 1.6 mcg/kg/day (p < 0.05). The Poisson regression indicated non-Caucasian race (p < 0.05), routine alcohol use (estimate = 0.03, p = 0.02), and osteoarthritis (estimate = -0.10, p < 0.001) in addition to known factors such as age (estimate = -0.003, p < 0.001), sex (female, estimate = -0.06, p < 0.001), and weight (estimate = 0.01, p < 0.001) were associated with the dosing of levothyroxine.

CONCLUSIONS

Along with weight, sex, age, and BMI, ML algorithms indicated that race, ethnicity, lifestyle and comorbidity factors also may impact levothyroxine dosing in post-thyroidectomy patients with benign conditions.

Clinical Presentation of Immune-Related Endocrine Adverse Events during Immune Checkpoint Inhibitor Treatment

The exact clinical course and factors associated with persistent endocrine immune-related adverse events (irAEs) are not well-established. Elucidation of these information will aid irAEs screening and follow-up planning for patients on immunotherapy. We analysed the clinical course of endocrine irAEs including thyroid and pituitary dysfunction and insulin-dependent diabetes mellitus (IDDM), identified factors associated with persistent thyroid dysfunction, and determined the association between endocrine irAEs and survival parameters. This retrospective observational study enrolled patients with metastatic cancer who underwent anti-PD-1, anti-PD-L1, and/or anti-CTLA-4 treatment and developed endocrine irAE at the National University Cancer Institute, Singapore, between June 2015 and December 2020. Sixty-six patients with endocrine irAE were evaluated, with a median follow-up time of 15.7 months. The median time to onset of thyroid dysfunction, pituitary dysfunction, and IDDM was 1.8 months (range: 0.3–15.8 months), 6.8 months (range: 1.5–27.3 months), and 7.8 months (range: 1.4–9.1 months), respectively. Positive thyroperoxidase antibodies (TPOAb) and/ or thyroglobulin antibodies (TgAb) status at the time of thyroid dysfunction was associated with persistent thyroid dysfunction (OR 11.6, 95% CI 1.3–570.8, p = 0.02; OR 8.8, 95% CI 1.3–106.9, p = 0.01, respectively). All patients with pituitary irAE had central hypocortisolism. All patients with IDDM had grade 4 irAE. Patients with endocrine irAE had longer median survival times. Endocrine irAEs were associated with nonprogressive disease. The screening and follow-up approach for endocrine irAEs should be tailored according to each endocrinopathy’s clinical course. Early screening is imperative given its wide median time to onset.

Rates of, and factors associated with, switching among generic levothyroxine preparations in commercially insured American adults

IMPORTANCE

Some practice guidelines warn against generic L-thyroxine preparation switching.

OBJECTIVE

To examine the rates of generic L-thyroxine preparation switching within one year of initiating L-thyroxine, and to examine factors associated with switching.

DESIGN AND SETTING

Retrospective study using national data from a large administrative claims database from January 2008 through November 2018.

PATIENTS

Medicare or commercially insured adults (≥18 years) who filled a generic L-thyroxine preparation.

MAIN OUTCOME MEASURES

At least one switch from one generic L-thyroxine preparation to another within 1 year of L-thyroxine initiation defined by prescription fills.

RESULTS

From January 2008 to November 2018, we included 483,390 patients who initiated generic L-thyroxine: mean (SD) age was 61.4 years (15.2), 75.2% were female, 72.6% were white. Within 1 year of initiating therapy, 98,013 (20%) switched to another L-thyroxine generic preparation at least once. In a multivariate logistic regression analysis, factors associated with switching included the number of pharmacies visited to fill L-thyroxine (>2 vs 1 adjusted OR [aOR] 7.15, 95% confidence interval [CI] 6.97-7.34), age ≥75 vs. <45 years (aOR 1.29, 95% CI 1.26-1.33), history of thyroid surgery (aOR 1.22, 95% CI 1.13-1.31), and first L-thyroxine fill date in 2018 vs. 2008 (aOR 3.32, 95% CI 3.14-3.51).

CONCLUSIONS AND RELEVANCE

One in five patients switched among generic L-thyroxine manufacturers within one year of treatment initiation. Generic L-thyroxine switching occurred more often when more pharmacies were used to fill L-thyroxine. Given existing guideline recommendations, additional studies should clarify the impact of generic L-thyroxine switching on thyroid hormone values.

Thyroid Function Alteration in Obesity and the Effect of Bariatric Surgery

The most common endocrine disease in obesity is hypothyroidism and secondary endocrine alterations, including abnormal thyroid function, are frequent in obesity. It is unclear whether impaired thyroid function is the cause or the consequence of increased adiposity; furthermore, there are no clear data regarding the best way to dose levothyroxine for patients with both hypothyroidism and obesity, and the effect of bariatric surgery (BS). The aim of the present article is to review some controversial aspects of the relation between obesity and the thyroid: (1) Thyroid function in obesity and the effect of BS (2) Thyroid hormone treatment (THT) in obese patients with hypothyroidism and the effect of BS. In summary: In morbidly obese patients, TSH is moderately increased. Morbid obesity has a mild central resistance to the thyroid hormone, reversible with weight loss. In morbidly obese hypothyroid patients, following weight loss, the levothyroxine dose/kg of ideal weight did not change, albeit there was an increment in the levothyroxine dose/kg of actual weight. From a clinical practice perspective, in morbid obesity, diagnosing mild hypothyroidism is difficult, BS improves the altered thyroid function and THT can be adapted better if it is based on ideal weight.

Optimized Replacement T4 and T4+T3 Dosing in Male and Female Hypothyroid Patients With Different BMIs Using a Personalized Mechanistic Model of Thyroid Hormone Regulation Dynamics

OBJECTIVE

A personalized simulation tool, p-THYROSIM, was developed (1) to better optimize replacement LT4 and LT4+LT3 dosing for hypothyroid patients, based on individual hormone levels, BMIs, and gender; and (2) to better understand how gender and BMI impact thyroid dynamical regulation over time in these patients.

METHODS

p-THYROSIM was developed by (1) modifying and refining THYROSIM, an established physiologically based mechanistic model of the system regulating serum T3, T4, and TSH level dynamics; (2) incorporating sex and BMI of individual patients into the model; and (3) quantifying it with 3 experimental datasets and validating it with a fourth containing data from distinct male and female patients across a wide range of BMIs. For validation, we compared our optimized predictions with previously published results on optimized LT4 monotherapies. We also optimized combination T3+T4 dosing and computed unmeasured residual thyroid function (RTF) across a wide range of BMIs from male and female patient data.

RESULTS

Compared with 3 other dosing methods, the accuracy of p-THYROSIM optimized dosages for LT4 monotherapy was better overall (53% vs. 44%, 43%, and 38%) and for extreme BMI patients (63% vs. ~51% low BMI, 48% vs. ~36% and 22% for high BMI). Optimal dosing for combination LT4+LT3 therapy and unmeasured RTFs was predictively computed with p-THYROSIM for male and female patients in low, normal, and high BMI ranges, yielding daily T3 doses of 5 to 7.5 μg of LT3 combined with 62.5-100 μg of LT4 for women or 75-125 μg of LT4 for men. Also, graphs of steady-state serum T3, T4, and TSH concentrations vs. RTF (range 0%-50%) for untreated patients showed that neither BMI nor gender had any effect on RTF predictions for our patient cohort data. Notably, the graphs provide a means for estimating unmeasurable RTFs for individual patients from their hormone measurements before treatment.

CONCLUSIONS

p-THYROSIM can provide accurate monotherapies for male and female hypothyroid patients, personalized with their BMIs. Where combination therapy is warranted, our results predict that not much LT3 is needed in addition to LT4 to restore euthyroid levels, suggesting opportunities for further research exploring combination therapy with lower T3 doses and slow-releasing T3 formulations.

Patient-Tailored Levothyroxine Dosage with Pharmacokinetic/Pharmacodynamic Modeling: A Novel Approach After Total Thyroidectomy

Background: After seven decades of levothyroxine (LT4) replacement therapy, dosage adjustment still takes several months. We have developed a decision aid tool (DAT) that models LT4 pharmacometrics and enables patient-tailored dosage. The aim of this was to speed up dosage adjustments for patients after total thyroidectomy. Methods: The DAT computer program was developed with a group of 46 patients post-thyroidectomy, and it was then applied in a prospective randomized multicenter validation trial in 145 unselected patients admitted for total thyroidectomy for goiter, differentiated thyroid cancer, or thyrotoxicosis. The LT4 dosage was adjusted after only two weeks, with or without application of the DAT, which calculated individual free thyroxine (fT4) targets based on four repeated measurements of fT4 and thyrotropin (TSH) levels. The individual TSH target was either <0.1, 0.1-0.5, or 0.5-2.0 mIU/L, depending on the diagnosis. Initial postoperative LT4 dosage was determined according to clinical routine without using algorithms. A simplified DAT with a population-based fT4 target was used for thyrotoxic patients who often went into surgery after prolonged TSH suppression. Subsequent LT4 adjustments were carried out every six weeks until target TSH was achieved. Results: When clinicians were guided by the DAT, 40% of patients with goiter and 59% of patients with cancer satisfied the narrow TSH targets eight weeks after surgery, as compared with only 0% and 19% of the controls, respectively. The TSH was within the normal range in 80% of DAT/goiter patients eight weeks after surgery as compared with 19% of controls. The DAT shortened the average dosage adjustment period by 58 days in the goiter group and 40 days in the cancer group. For thyrotoxic patients, application of the simplified DAT did not improve the dosage adjustment. Conclusions: Application of the DAT in combination with early postoperative TSH and fT4 monitoring offers a fast approach to LT4 dosage after total thyroidectomy for patients with goiter or differentiated thyroid cancer. Estimation of individual TSH-fT4 dynamics was crucial for the model to work, as removal of this feature in the applied model for thyrotoxic patients also removed the benefit of the DAT.

Evaluation of Thyroid Hormone Replacement Dosing in Morbidly Obese Hypothyroid Patients after Bariatric Surgery-Induced Weight Loss

The most frequent endocrine disease in obese patients is hypothyroidism. To date, there are no clear data regarding what happens to the dose of levothyroxine (LT4) after bariatric surgery (BS). The objective of the present study was to evaluate thyroid hormone replacement dose in morbidly obese hypothyroid patients after BS-induced weight loss. We explore the best type of measured or estimated body weight for LT4 dosing. We performed an observational study evaluating patients with morbid obesity and hypothyroidism who underwent BS. We included 48 patients (three men). In morbidly obese hypothyroid patients 12 months after BS-induced weight loss, the total LT4 dose or the LT4 dose/kg ideal body weight did not change, while there was a significant increase in LT4 dose/body surface area, LT4 dose/kg weight, LT4 dose/kg adjusted body weight, LT4 dose/kg body fat, and LT4 dose/kg lean body weight. There were no differences in LT4 dose and its variation between sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB). The present study strongly suggests that LT4 dosing in obese hypothyroid patients can be individually adapted more precisely if it is based on ideal body weight.

Appropriate dose of levothyroxine replacement therapy for hypothyroid obese patients

Background

Athyreotic patients require a daily levothyroxine (LT4) doses of 1.6-1.8 mcg/kg of actual body weight (BW) to achieve normal thyroid stimulating hormone (TSH) levels. Lean body mass (LBM) calculation may be a more accurate determination of LT4 dose in obese patients. Previous studies were mainly investigated in Caucasians and LBM is markedly different between various ethnic groups. We aim to identify the optimal dose of LT4 replacement therapy in hypothyroid Thai patients including obese subjects.

Methods

We retrospectively reviewed the medical records of Thai adults with hypothyroidism at the thyroid clinic. Patients had been received LT4 (Brand: Euthyrox) at a stable dose ≥ 75 mcg/day for at least 1 year. Patients with thyroid cancer, pregnant, and lactating women were excluded. LBM was calculated by the Hume formula.

Results

Two hundred patients (80% females) with a mean age of 48.6 ± 14.8 years and a body mass index (BMI) of 24.5 ± 4.6 kg/m² were included. Daily LT4 dose/kg of actual BW according to BMI 18.5-24.9, 25-29.9, and ≥ 30 kg/m² were 1.67 ± 0.27, 1.51 ± 0.28 and 1.39 ± 0.34 mcg/kg, respectively. In contrast, LT4 dose/kg of LBM were 2.31 ± 0.39, 2.35 ± 0.45 and 2.36 ± 0.51 mcg/kg, respectively.

Conclusions

LBM is considered a better indicator for calculating an appropriate LT4 replacement dose than actual BW in hypothyroid obese Thai patients. The recommended daily dose of LT4 is 2.3 mcg/kg of LBM that could be applied for all ranges of BMI.

Comparison of Dosing Schemes for Thyroid Hormone Replacement Therapy After Thyroidectomy

BACKGROUND

Current thyroid hormone replacement therapy (THRT) is built on weight-based standard calculation of dose. A novel Poisson regression model, which accounts for seven clinical variables, was recently proposed to improve accuracy of THRT. We aimed to compare the accuracy of estimated THRT dose to reach euthyroid and the difference in predicted dose between the Poisson (scheme A) and the weight-based standard (scheme B) in patients following total thyroidectomy for benign disease.

METHODS

We retrospectively reviewed medical record of patients who underwent total or completion thyroidectomy for benign disease at a single institution between 2011 and 2019. The THRT dose was calculated using both schemes. We compared the difference between calculated THRT and prediction rates for optimal THRT dosing needed to achieve a euthyroid state between dosing schemes. Patients were evaluated for achieving euthyroid state, defined as TSH 0.45-4.5 mIU/L. We also compared dosing error rates (> 25 mcg over- and underdosing) between schemes. Prediction rates were compared by BMI tertiles to account for the effect of BMI extremes in achieving euthyroid state. The difference in predicted dose between schemes was calculated in both the total sample size and patients that met euthyroid. A measure of agreement, Kappa, was used to estimate agreement between dosing schemes.

RESULTS

A total of 406 patients underwent total thyroidectomy for benign disease, with 184 having sufficient follow up data confirming euthyroid state. Of the 184 patients, 85.9% (n = 158) were women, 81% (n = 149) were Hispanic, and 56.5% (n = 104) were obese with a median BMI of 30.8 kg/m2. Scheme A resulted in a higher, but not statistically significant, accuracy rate (A: 60.3%, n = 111 versus B: 53.8%, n = 99; P = 0.21). Overdosing errors were lower with Scheme A (A:17.9% versus B: 32.1%; P = 0.0025) and less extreme > 25 µg (A: 17.9% versus B: 26.1%; P = 0.08). A trend in improved accuracy in patients with a BMI > 35 kg/m2 was noted (A: 46.9% versus B: 34.4%; P = 0.20). Scheme A also resulted in less overdosing errors in obese patients compared to Scheme B (A: 19.2% versus 45.2%; P = 0.0006). The average difference in predicted dose between schemes was an entire dose difference, mean of 16.0 µg and 15.8 µg for the total and euthyroid samples respectively. Furthermore, for the majority of patients the predicted dose did not match between the two dosing schemes for total and euthyroid samples, 76% (n = 311) and 76% (n = 141) respectively. In patients that achieved euthyroid, agreement between dosing schemes was low to moderate (Kappa = 0.360).

CONCLUSIONS

Lower rates of overdosing were found for scheme A, particularly with obese patients. No statistically significant differences in predicted THRT dose was observed between schemes. The difference in predicted dose between schemes was on average 15 ug, correlating with an entire dose. The consideration of clinical variables other than weight (scheme A) when determining optimal THRT dosing may be of importance to prevent overdoses, with particular clinical relevance in patients with higher BMIs.