Levothyroxine dose adjustment in hypothyroid patients following gastric sleeve surgery

Effect of Laparoscopic Sleeve Gastrectomy on Thyroid Function Tests and Levothyroxine Doses in People With Obesity

INTRODUCTION

We investigated how laparoscopic sleeve gastrectomy (LSG) affected serum levels of thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) in obese patients with hypothyroidism. We additionally examined whether the dose of levothyroxine decreases as a result of weight loss in this study.

MATERIALS AND METHODS

Fifty-one people with obesity who received levothyroxine treatment for hypothyroidism and underwent LSG between January 2017 and January 2023 were retrospectively examined. Weight, body mass index (BMI), TSH, FT4, FT3, weekly levothyroxine dose changes, and weight-adjusted levothyroxine doses before surgery and the sixth month after surgery were compared.

RESULTS

Among the 51 patients included in this study, 50.98% ceased the use of levothyroxine, and nearly half (41.18%) required an adjustment of their levothyroxine dose during the follow-up period (sixth month). Notably, the total weekly dose of levothyroxine (mcg) decreased in the sixth month following surgery (p<0.001). The weekly weight-adjusted dose (mcg/kg) decreased during the same time frame (p<0.001). The preoperative total weekly dose of levothyroxine, EWL% and absence of hyperlipidemia were found to be the independent predictors of the weight-adjusted weekly levothyroxine dose change (p<0.001, p=0.038, and p=0.044, respectively).

CONCLUSIONS

Thyroid function tests in people with obesity can show improvement after LSG. LSG may reduce the weight-adjusted dose of levothyroxine at six months postoperatively and therefore patients should be monitored for possible levothyroxine dose readjustments based on weight loss.

Total weight loss induces the alteration in thyroid function after bariatric surgery

Background

Bariatric surgery is an effective approach to weight loss, which may also affect thyroid function. However, alteration in thyroid-stimulating hormone (ΔTSH) and thyroid hormones after bariatric surgery and the relationship between thyroid function and postoperative weight loss still remains controversial.

Methods

Data were collected from euthyroid patients with obesity who underwent sleeve gastrectomy and Roux-en-Y gastric bypass from 2017 to 2022. The alterations of free thyroxine (FT4), free triiodothyronine (FT3), total thyroxine (TT4), total triiodothyronine (TT3), and TSH were calculated 1 year after surgery. Pearson correlation analysis was used to assess the correlation between the percentage of total weight loss (%TWL) and ΔTSH. Multivariable linear regression was utilized to determine the association between %TWL and ΔTSH.

Results

A total of 256 patients were included in our study. The mean %TWL was 28.29% after 1 year. TSH decreased from 2.33 (1.67, 3.04) uIU/mL to 1.82 (1.21, 2.50) uIU/mL (P < 0.001), FT3 decreased from 3.23 ± 0.42 pg/mL to 2.89 ± 0.41 pg/mL (P < 0.001), FT4 decreased from 1.11 ± 0.25 ng/dL to 1.02 ± 0.25 ng/dL (P < 0.001), TT3 decreased from 1.13 (1.00, 1.25) ng/mL to 0.89 (0.78, 1.00) ng/mL (P < 0.001), and TT4 decreased from 8.28 ± 1.69 ug/mL to 7.82 ± 1.68 ug/mL 1 year postoperatively (P < 0.001). %TWL was found to be significantly correlated to ΔTSH by Pearson correlation analysis (Pearson correlation coefficient = 0.184, P = 0.003), indicating that the more weight loss, the more TSH declined. After adjusting for covariates in multivariable linear regression, %TWL was found to be independently associated with ΔTSH (β = 0.180 [95% confidence interval (CI), 0.048 - 0.312], P = 0.008). Moreover, %TWL was divided into 3 categorical groups (%TWL ≤ 25%, 25% < %TWL ≤ 35%, and %TWL > 35%) for further exploration, and was also found to be an independent predictor for ΔTSH after adjusting for covariates in multivariable linear regression (β = 0.153 [95% CI, 0.019 - 0.287], P = 0.025).

Conclusion

TSH, FT4, FT3, TT4, and TT3 decrease significantly 1 year after bariatric surgery. The decline in TSH is independently mediated by postoperative weight loss; the more the weight loss, the more the TSH decrease.

Impact of Bariatric Surgery in the Short and Long Term: A Need for Time-Dependent Dosing of Drugs

Sparse information is available on pharmacokinetic changes of drugs over time after bariatric surgery. By reviewing the literature on the short- and long-term pharmacokinetic changes of drugs, several patterns were identified for 39 drugs. No relevant pharmacokinetic changes were identified for roughly a third of the drugs. Of the remaining drugs, levels were variable and partly unpredictable shortly after the surgery. In the long term, most of the drug levels remain altered, but in some cases they returned to preoperative values. Based on the changes and the efficacy-safety balance of each drug, clinicians may need to perform additional clinical monitoring for specific drugs, including measuring drug levels. This review provides suggestions for clinicians and pharmacists for specific time-dependent drug dosing advice.

Getting the levothyroxine (LT4) dose right for adults with hypothyroidism: opportunities and challenges in the use of modern LT4 preparations

Lifelong treatment with levothyroxine (LT4) is the mainstay of management for individuals with hypothyroidism. Many hypothyroid patients start LT4 treatment at a low dose (e.g. 25-50 µg), especially the elderly, those with residual thyroid function, those with low body weight, and those with significant (especially cardiac) comorbidities. Almost half of patients on LT4 replacement therapy demonstrate either under- or over-treatment. Many LT4 preparations have relatively large intervals between tablet strengths at the lower end of their dose ranges (providing 25 µg, 50 µg, and 75 µg tablets), which may represent a barrier to achieving the optimum maintenance treatment for some patients. The availability of intermediate tablet strengths of LT4 in the 25-75 µg range may facilitate precise and effective dose titration of LT4 and may also enable convenient maintenance regimens based on a single LT4 tablet daily, to support adherence to therapy.

Factors influencing the levothyroxine dose in the hormone replacement therapy of primary hypothyroidism in adults

Levothyroxine (LT4) is a safe, effective means of hormone replacement therapy for hypothyroidism. Here, we review the pharmaceutical, pathophysiological and behavioural factors influencing the absorption, distribution, metabolism and excretion of LT4. Any factor that alters the state of the epithelium in the stomach or small intestine will reduce and/or slow absorption of LT4; these include ulcerative colitis, coeliac disease, bariatric surgery, Helicobacter pylori infection, food intolerance, gastritis, mineral supplements, dietary fibre, resins, and various drugs. Once in the circulation, LT4 is almost fully bound to plasma proteins. Although free T4 (FT4) and liothyronine concentrations are extensively buffered, it is possible that drug- or disorder-induced changes in plasma proteins levels can modify free hormone levels. The data on the clinical significance of genetic variants in deiodinase genes are contradictory, and wide-scale genotyping of hypothyroid patients is not currently justified. We developed a decision tree for the physician faced with an abnormally high thyroid-stimulating hormone (TSH) level in a patient reporting adequate compliance with the recommended LT4 dose. The physician should review medications, the medical history and the serum FT4 level and check for acute adrenal insufficiency, heterophilic anti-TSH antibodies, antibodies against gastric and intestinal components (gastric parietal cells, endomysium, and tissue transglutaminase 2), and Helicobacter pylori infection. The next step is an LT4 pharmacodynamic absorption test; poor LT4 absorption should prompt a consultation with a gastroenterologist and (depending on the findings) an increase in the LT4 dose level. An in-depth etiological investigation can reveal visceral disorders and, especially, digestive tract disorders.

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.

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.

Hypothyroidism and levothyroxine therapy following bariatric surgery: a systematic review, meta-analysis, network meta-analysis, and meta-regression

BACKGROUND

Many health benefits of bariatric surgery are known and well-studied, but there is scarce data on the benefits of bariatric surgery on the thyroid function.

OBJECTIVE

We aimed to make a meta-analysis regarding the impact of bariatric surgery on thyroid-stimulating hormone (TSH) levels, levothyroxine dose, and the status of subclinical hypothyroidism.

SETTING

Systematic review and meta-analysis.

METHODS

PubMed, EMBASE, and Cochrane Library were searched up to December 2020 for relevant clinical studies. Random-effects model was used to pool results. Network meta-analysis was performed, incorporating direct and indirect comparisons among different types of bariatric surgery. Meta-regression analysis was performed to evaluate the impact of moderator variables on TSH levels and required levothyroxine dose after surgery. We followed the PRISMA guidelines for data selection and extraction. PROSPERO registry number: CRD42018105739.

RESULTS

A total of 28 studies involving 1284 patients were included. There was a statistically significant decrease in TSH levels after bariatric surgery (mean difference = -1.66 mU/L, 95%CI [-2.29, -1.03], P < .0001). In meta-regression analysis, we found that the following moderator variables: length of follow-up, mean age, baseline TSH, and preoperative thyroid function, could explain 1%, 43%, 68%, and 88% of the between-study variance, respectively. Furthermore, subclinical hypothyroidism was completely resolved in 87% of patients following bariatric surgery. In addition, there was a statistically significant decrease of levothyroxine dose in frank hypothyroid patients following bariatric surgery (mean difference = -13.20 mcg/d, 95%CI [-19.69, -6.71]). In network meta-analysis, we found that discontinuing or decreasing levothyroxine dose was significant following Roux-en-Y gastric bypass, 1 anastomosis gastric bypass, and sleeve gastrectomy, (OR = 31.02, 95%CI [10.34, 93.08]), (OR = 41.73, 95%CI [2.04, 854.69]), (OR = 104.03, 95%CI [35.79, 302.38]), respectively.

CONCLUSIONS

Based on our meta-analysis, bariatric surgery is associated with the resolution of subclinical hypothyroidism, a decrease in TSH levels, and a decrease in levothyroxine dose.