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

Pseudo-Malabsorption in High Dose Levothyroxine-Resistant Hypothyroidism

A 38-year-old woman was diagnosed with hypothyroidism during pregnancy at age 35 years and started on levothyroxine (LT4). Despite increasing the dose to 400 μg/day and adding liothyronine, her thyroid function did not improve, leading to hospitalization. Upon admission, her thyroid-stimulating hormone (TSH), free triiodothyronine (T3), and free thyroxine (T4) levels were 255 μIU/mL (255 mIU/L) (reference range [RR]: 0.35---4.94 μIU/mL; 0.35---4.94 mIU/L), 3.42 pg/mL (5.27 pmol/L) (RR: 1.71-3.71 pg/mL; 2.63-5.70 pmol/L), and 0.153 ng/dL (1.97 pmol/L) (RR: 0.70-1.48 ng/dL; 9.01-19.05 pmol/L), respectively. She reported good adherence to medication and not consuming interfering food or medication. Endoscopic examination revealed no malabsorption. A 1000-μg oral LT4 loading test showed an increase in free T4 level from 0.787 (10.1 pmol/L) to 2.40 ng/dL (30.9 pmol/L), indicating pseudo-malabsorption. After presenting the loading test results, she admitted to nonadherence. A multidisciplinary team intervened, conducting individual counseling and simplifying treatment. Post-discharge, with LT4 200 μg/day, her TSH, free T3, and free T4 levels improved to 0.496 μIU/mL (0.496 mIU/L), 5.23 pg/mL (8.05 pmol/L), and 2.19 ng/dL (28.2 pmol/L), respectively. When addressing treatment-resistant hypothyroidism, it is crucial to evaluate patient history and medication schedule and to check for malabsorption. Comprehensive interventions are recommended if nonadherence is suspected.

Effects of timing and scheduling in levothyroxine adherence to hypothyroidism control: Meta-analysis with trial sequential analysis of Randomized Clinical Trials

PURPOSE

Treatment adherence for chronic conditions is a common clinical challenge. This systematic review aimed to assess the impact of scheduling and timing on levothyroxine adherence in patients with hypothyroidism.

METHODS

We searched multiple databases (PubMed, EMBASE, SCOPUS, Web Of Science, and CINAHL) using relevant terms related to hypothyroidism and medication adherence. Two independent reviewers conducted study selection, evaluation, and data extraction. The primary outcome was thyrotropin (TSH) levels, analyzed using inverse-variance meta-analysis. Trial sequential analysis (TSA) was conducted to assess the statistical reliability of the meta-analyses results.

RESULTS

Of the 706 articles initially found, 11 met the inclusion criteria: eight assessed evening administration and three evaluated weekly administration of levothyroxine. Comparison between evening and morning administration showed no significant difference in changes of TSH levels (dTSH 0.18; 95% confidence interval [95%CI] -0.29-0.65, P = 0.46). However, considering weekly administration of levothyroxine, TSH levels were higher in the experimental group (dTSH 1.14; 95%CI 0.80-1.14, P < 0.01), although the mean final TSH remained within the reference range in both groups. TSA indicated that the required information size was achieved for scheduling interventions.

CONCLUSION

Both daily timing and weekly administration of levothyroxine were effective in maintaining TSH levels within reference values. Individualized dosing regimens may be considered based on patient convenience and preference.

Developing a machine learning-based predictive model for levothyroxine dosage estimation in hypothyroid patients: a retrospective study

Hypothyroidism, a common endocrine disorder, has a high incidence in women and increases with age. Levothyroxine (LT4) is the standard therapy; however, achieving clinical and biochemical euthyroidism is challenging. Therefore, developing an accurate model for predicting LT4 dosage is crucial. This retrospective study aimed to identify factors affecting the daily dose of LT4 and develop a model to estimate the dose of LT4 in hypothyroidism from a cohort of 1,864 patients through a comprehensive analysis of electronic medical records. Univariate analysis was conducted to explore the relationships between clinical and non-clinical variables, including weight, sex, age, body mass index, diastolic blood pressure, comorbidities, food effects, drug-drug interactions, liver function, serum albumin and TSH levels. Among the models tested, the Extra Trees Regressor (ETR) demonstrated the highest predictive accuracy, achieving an R² of 87.37% and the lowest mean absolute error of 9.4 mcg (95% CI: 7.7-11.2) in the test set. Other ensemble models, including Random Forest and Gradient Boosting, also showed strong performance (R² > 80%). Feature importance analysis highlighted BMI (0.516 ± 0.015) as the most influential predictor, followed by comorbidities (0.120 ± 0.010) and age (0.080 ± 0.005). The findings underscore the potential of machine learning in refining LT4 dose estimation by incorporating diverse clinical factors beyond traditional weight-based approaches. The model provides a solid foundation for personalized LT4 dosing, which can enhance treatment precision and reduce the risk of under- or over-medication. Further validation in external cohorts is essential to confirm its clinical applicability.

Therapeutic efficacy and patient compliance of levothyroxine liquid and softgel formulations taken with meals: a systematic review

PURPOSE

Levothyroxine (L-T4) is the drug of choice for treating primary hypothyroidism. L-T4 tablets should be taken at least 30 min before breakfast. Several studies have suggested that serum thyroid profile is not affected by concomitant intake of liquid/softgel L-T4 with meals. Our aim is to review the evidence on therapeutic efficacy and patient compliance with the liquid and softgel formulation of L-T4 taken with meals, also compared with the standard tablet therapy regimen, in hypothyroid patients.

METHODS

We performed a systematic review of literature by searching PubMed, Embase, and Cochrane Library databases. PRISMA guidelines were applied, and the risk of bias of the included studies was assessed using the RoB 2 and ROBINS tools. The methodological quality was assessed following the GRADE criteria.

RESULTS

We included 13 studies, accounting for a total of 1697 patients. The timing of liquid L-T4 intake from breakfast did not affect the therapeutic efficacy of the treatment. No significant differences in the absorption of liquid L-T4 were found when administered together with different foods, beverages, drugs, or other supplements. TSH levels are not influenced by taking softgel L-T4 at breakfast; the efficacy of softgel and liquid formulation is similar when they are taken with a meal, but superior to that of tablet formulation. Shifting from L-T4 tablets taken 30 min before breakfast to liquid/softgel formulation taken with the meal improved medication adherence and perceived quality of life of patients.

CONCLUSION

Liquid and softgel formulation of L-T4 can be taken at breakfast or close to meals, without losing therapeutic efficacy. These formulations could also improve patient compliance and quality of life compared to L-T4 tablet therapy taken 30 min before breakfast.

Thyroid function status in patients with hypothyroidism on thyroxine replacement and associated factors: a retrospective cohort study in primary care

BACKGROUND

Long-term management of patients with hypothyroidism on thyroxine replacement requires thyroid function test (TFT) monitoring once every six-12 months as recommended by clinical practice guidelines. This study determined their thyroid function status during two-year follow-up visits in primary care, and the factors influencing their thyroid status, and assessed the optimal interval for TFTs.

METHODS

A retrospective cohort study was conducted on adults with a clinical diagnosis code for hypothyroidism in their electronic health records taken from a group of polyclinics in Singapore between July 2017 and June 2020. The follow-up thyroid status was categorized as under-replacement (TSH ≥ 3.70mIU/L), over-replacement (TSH ≤ 0.65mIU/L) or euthyroid (TSH 0.65-3.70mIU/L). The patients' demographic, clinical and TFT data were analyzed using appropriate statistical tests during the two-year follow-up. Stepwise logistic regression analysis identified the factors associated with suboptimal thyroid control. Kaplan-Meier analysis was used to compare their thyroid function status in association with the interval between TFT monitoring.

RESULTS

Data from 5,749 eligible subjects (mean age 62.1 ± 13.29 years; 79% female; 79.7% Chinese) were analyzed. After a two-year follow-up, 61.9% (n = 3558) of all subjects were euthyroid, with 29.5% (n = 1694) being under-replaced and 8.6% (n = 497) over-replaced. However, thyroid status did not differ significantly with the various dose regimen (daily, segmented, or alternate days) (p = 0.193). Stepwise logistic regression showed that thyroxine under-replacement was significantly associated with the male gender (AOR = 1.25,95%CI = 1.03-1.51,p = 0.02) and obesity (AOR = 1.34,95%CI = 1.08-1.66,p = 0.008). Every unit (μg/kg body weight) increase in the mean daily thyroxine dose was associated with 2.72 times greater odds of over-replacement. When comparing thyroid function monitoring at intervals of 13-24 months, monitoring at shorter intervals (≤ 12 months) was less likely to detect thyroxine under-replacement (AOR = 0.57,95%CI = 0.44-0.74,p < 0.001) and over-replacement (AOR = 0.62,95%CI = 0.41-0.97,p = 0.033). Among the 3,312 adults who were euthyroid at baseline, 22.2%, 41.7% and 59.6% had suboptimal thyroid control at 6, 12 and 24 months respectively (Kaplan-Meier analysis).

CONCLUSION

Around six in ten patients were euthyroid with thyroxine replacement for hypothyroidism in primary care over two years. Thyroxine under-replacement was associated with male gender and obesity. The proportion of euthyroid patients developing abnormal thyroid function doubled with TFTs at six, 12 and 24-month intervals.

One sip of water with LT-4 supplementation-a key to euthyroidism in Hashimoto's thyroiditis

PURPOSE

Recommended pharmacotherapy for hypothyroidism in Hashimoto's thyroiditis (HT) is oral supplementation with levothyroxine (LT-4). However, serum thyrotropin (TSH) levels within normal range are not consistently achieved with LT-4 medication.

PATIENTS AND METHODS

We report on 35 HT patients with LT-4 therapy in this retrospective evaluation. In general, we recommend that a maximum of two sips of water, which would then amount to < 50 mL, be ingested at the same time as LT-4. We report on follow up examinations measuring TSH and antibodies against thyroid peroxidase (TPOAb) after 6 months to five years.

RESULTS

After median time of 643 days (range 98-1825) we found in 35 HT patients a statistical significant reduction of serum TSH (p < 0.001) and TPOAb (p = 0.006). The patients median body weight was 71 kg (range 48-98) and a daily LT-4 dosage was used with median 69.1 µg (range 25-150). This results in a daily LT-4 dose of median 1.01 µg/kg bodyweight (range 0.3-2.3).

CONCLUSIONS

The reduction of water ingestion to a maximum of two sips, which is <50 mL, combined with LT-4 supplementation helps to achieve euthyroidism in HT. In addition, it reduces the L-T4 medication dosage needed to lower TSH serum levels and decreases TPO antibodies in HT.

Morning exercise affects the absorption of oral levothyroxine: a single center pilot study

PURPOSE

Levothyroxine (LT4) is the first-line hormone replacement therapy for hypothyroidism. Several factors which have an influence on oral LT4 absorption have been previously described; however, the influence of exercise on oral LT4 absorption has not been reported, yet. It was aimed to investigate the possible effect of morning exercise, right after LT4 ingestion, on the absorption of LT4 tablets in this study.

PATIENTS AND METHODS

Patients with primary hypothyroidism who fulfilled the inclusion criteria were offered to participate in a 6-week morning exercise programme and those who agreed to participate were enrolled in our study. Patients were required to have a walk for 30 min with a regular speed right after taking their daily LT4 treatments and start having breakfast the first hour after LT4 intake. Pre- and post-exercise TSH levels were recorded and TSH percentage change was calculated.

RESULTS

All patients had decreased TSH levels after the exercise programme. There was a significant decrease in TSH levels (p < 0.001). A significant positive correlation between TSH percentage change and daily dose of LT4 per kg of body weight was also shown.

CONCLUSIONS

This is the first study which demonstrates the significant positive effect of morning exercise on the absorption of LT4 tablets. In addition to that, it was also found that as the daily dose of LT4 increases, the percentage decrease of TSH level becomes greater.

Diagnostic and therapeutic value of human serpin family proteins

SERPIN (serine proteinase inhibitors) is an acronym for the superfamily of structurally similar proteins found in animals, plants, bacteria, viruses, and archaea. Over 1500 SERPINs are known in nature, while only 37 SERPINs are found in humans, which participate in inflammation, coagulation, angiogenesis, cell viability, and other pathophysiological processes. Both qualitative or quantitative deficiencies or overexpression and/or abnormal accumulation of SERPIN can lead to diseases commonly referred to as "serpinopathies". Hence, strategies involving SERPIN supplementation, elimination, or correction are utilized and/or under consideration. In this review, we discuss relationships between certain SERPINs and diseases as well as putative strategies for the clinical explorations of SERPINs.

Probiotics and Prebiotics in Subclinical Hypothyroidism of Pregnancy with Small Intestinal Bacterial Overgrowth

Evaluating efficacy of probiotics combined with prebiotics in small intestinal bacterial overgrowth (SIBO) in subclinical hypothyroidism (SCH) in the second trimester. We collected data from 78 pregnant women with SCH (SCH group) and 74 normal pregnant women (control group) in second trimester, compare the differences in high sensitivity C-reactive protein (hsCRP), result of lactulose methane-hydrogen breath test and gastrointestinal symptoms assessed by GSRS scale between two groups. In SCH group, 32 patients with SIBO were selected as intervention group. Treatment with probiotics + prebiotics for 21 days; The differences of lipid metabolism, hsCRP, thyroid function level, methane-hydrogen breath test results and GSRS scores before and after treatment were compared to evaluate the therapeutic effect. (1) The positive rate of SIBO and methane, hsCRP levels in SCH group were higher than those in control group (P < 0.05), the total score of GSRS scale, mean score of indigestion syndrome, and constipation syndrome in SCH group were higher (P < 0.05). (2) The mean abundance of hydrogen and methane were higher in SCH group. (3) After treatment, serum levels of thyrotropin(TSH), total cholesterol(TC), triglyceride(TG), low-density lipoprotein (LDL), and hsCRP in intervention group were decreased, and high-density lipoprotein (HDL) was increased compared with before treatment (P < 0.05). (4) After treatment, methane positive rate, total score of GSRS scale, mean score of diarrhea syndrome, dyspepsia syndrome, and constipation syndrome were decreased (P < 0.05). (5) The average abundance of methane and hydrogen were lower. Probiotics combined with prebiotics are effective in the treatment of SIBO in pregnant SCH patients.Clinical Trial Registration Number: ChiCTR1900026326.

Association of pharmacogenomic, clinical and behavioural factors with oral levothyroxine (LT-4) dose of hypothyroid patients in Sri Lanka: a matched case control study

BACKGROUND

Hypothyroidism is a common endocrine disorder that exerts a substantial influence on people all over the world. Levothyroxine (LT-4) is the drug of choice for the treatment of hypothyroidism and the starting oral dose is typically ranging from 1.5 to 1.7 µg/kg/day. The target is to achieve an optimum serum TSH level of 0.4-4.0 mIU/L; hence, the dose is titrated accordingly. Once the LT-4 dose is adjusted to obtain the target TSH level, it usually remains stable for a long period of time in most cases. However, some of the patients require frequent dose adjustments and some of them require unusually high doses. Therefore, the aim of this study is to determine the association of pharmacogenomic, clinical and behavioural factors with the oral levothyroxine (LT-4) dose requirement of hypothyroid patients in Sri Lanka.

METHOD

This study will be conducted as a matched case-control study and will involve primary hypothyroid patients who visit the diabetes and endocrinology clinic at the National Hospital, Kandy, Sri Lanka. We will recruit a total of 292 cases and select 292 controls from the clinic who are matched in terms of age, sex and Body Mass Index (BMI). An interviewer-administered questionnaire will be used to collect data from the participants (n = 584). Of the 584 patients, blood samples will be collected from a sub-sample (n = 150) for DNA extraction. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) will be performed for single nucleotide polymorphisms (SNP) analysis.

DISCUSSION

Frequent dose adjustments of levothyroxine cause a serious economic burden to the healthcare system. By identifying the root causes of the variations in LT-4 dosage, a more comprehensive comprehension of hypothyroidism and its management can be attained in Sri Lanka. Furthermore, upon identification of a positive association/correlation between genetic polymorphisms and the LT-4 dose, SNP profiles can be used as a possible genetic marker for dose adjustment determination in future patients.

Association of DIO2 and MCT10 Polymorphisms With Persistent Symptoms in LT4-Treated Patients in the UK Biobank

CONTEXT

Some evidence suggests gene-treatment interactions might cause persistent symptoms in individuals receiving levothyroxine (LT4) treatment.

OBJECTIVE

We investigated, as previously hypothesized, if single-nucleotide variations (SNVs; formerly single-nucleotide polymorphisms) in rs225014 (Thr92Ala), rs225015, or rs12885300 (ORFa-Gly3Asp) in the deiodinase 2 gene (DIO2), or rs17606253 in the monocarboxylate transporter 10 gene (MCT10) were associated with outcomes indicative of local tissue hypothyroidism in LT4-treated patients and controls.

METHODS

We included 18 761 LT4-treated patients and 360 534 controls in a population-based cross-sectional study in the UK Biobank. LT4 treatment was defined as a diagnosis of hypothyroidism and self-reported use of LT4 without use of 3,5,3'-triiodothyronine. Outcomes were psychological well-being, cognitive function, and cardiovascular risk factors. Associations were evaluated by linear, logistic, or ordinal logistic multiple regression. Adjustments included sex, age, sex-age interaction, and genetic principal components 1 to 10.

RESULTS

Compared to controls, LT4 treatment was adversely associated with almost all outcomes, most noteworthy: Increased frequency of tiredness (P < .001), decreased well-being factor score (P < .001), increased reaction-time (P < .001), and increased body mass index (P < .001). Except for a significant association between the minor rs225015 A allele and financial dissatisfaction, there was no association of rs225014, rs225015, rs12885300, or rs17606253 with any outcomes in LT4-treated patients. For all outcomes, carrying the risk allele at these 4 SNVs did not amplify symptoms associated with LT4 treatment compared to controls.

CONCLUSION

rs225014, rs225015, rs12885300, and rs17606253 could not explain changed psychological well-being, cognitive function, or cardiovascular risk factors in LT4-treated patients. Our findings do not support a gene-treatment interaction between these SNVs and LT4 treatment.

Levothyroxine and Non-alcoholic Fatty Liver Disease: A Mini Review

Levothyroxine or l-thyroxine is artificially manufactured thyroxine, which is used as a drug to treat underactive thyroid conditions in humans. The drug, levothyroxine, is consumed daily in a prescribed dose to replace the missing thyroid hormone thyroxine in an individual with an underactive thyroid, and it helps to maintain normal physiological conditions. Though it is a life-maintaining drug, it replaces the missing thyroid hormone and performs the necessary daily metabolic functions in our body. Like all other allopathic drugs, it comes with certain side effects, which include joint pain, cramps in muscle, weight gain/loss, hair loss, etc. The thyroid hormone, thyroxine, is known to mobilize fat in our body, including the ones from the hepatic system. An underactive thyroid may cause an accumulation of fat in the liver, leading to a fatty liver, which is clinically termed Non-Alcoholic Fatty Liver Disease (NAFLD). The correlation between hypothyroidism and NAFLD is now well-studied and recognized. As levothyroxine performs the functions of the missing thyroxine, it is anticipated, based on certain preliminary studies, that the drug helps to mobilize hepatic fat and thus may have a crucial role in mitigating the condition of NAFDL.

Refractory Hypothyroidism: Unraveling the Complexities of Diagnosis and Management

INTRODUCTION

Refractory hypothyroidism (RH) represents a challenge in the diagnosis and treatment within the field of thyroidology. It is defined as the inability to achieve disease control despite using levothyroxine (LT4) doses of 1.9 μg/kg/d or higher.

METHODS

A comprehensive review, encompassing 103 articles, was conducted using the Scielo, Scopus, and EMBASE databases, providing an approach to evaluation and diagnosis of this condition.

RESULTS

LT4 disintegrates and dissolves within an acidic gastric environment before being absorbed in the jejunum and ileum. It then extensively binds to serum transporter proteins and undergoes deiodination to yield tri-iodothyronine, the biologically active hormone. There are various nonpathological causes of RH, such as noncompliance with treatment, changes in the brand of LT4, food and drug interferences, as well as pregnancy. Pathological causes include lactose intolerance, Helicobacter pylori infection, giardiasis, among others. The diagnosis of RH involves conducting a thorough medical history and requesting relevant laboratory tests to rule out causes of treatment resistance. The LT4 absorption test allows for the identification of cases of malabsorption. The treatment of RH involves identifying and addressing the underlying causes of noncompliance or malabsorption. In cases of pseudomalabsorption, supervised and weekly administration of LT4 may be considered.

DISCUSSION

Early recognition of RH and correction of its underlying cause are of utmost importance, as this avoids the use of excessive doses of LT4 and prevents cardiovascular and bone complications associated with this condition.

The Use of Levothyroxine Absorption Tests in Clinical Practice

Although levothyroxine (LT4) is a widely prescribed drug, more than 30% of LT4-treated patients fail to achieve the recommended serum level of thyrotropin with a body weight-based dose of LT4. An LT4 absorption test (LT4AT) is part of the workup for confirming normal LT4 absorption or diagnosing malabsorption. We searched PubMed with the terms levothyrox*, L-T4, LT4, TT4, FT4, FT3, TT3, test, loading, uptake, absorp*, "absorb*, bioavailab*, bioequiv* malabsorb*, and pseudomalabsorb*. A total of 43 full-text publications were analyzed. The published procedures for LT4AT differ markedly in the test dose, formulation, test duration, frequency of blood collection, analyte (total thyroxine [TT4] or free thyroxine [FT4]), metric (absolute or relative peak or increment, or area under the curve) and the threshold for normal absorption. In a standardized LT4AT for routine use, the physician could advise the patient to not consume food, beverages, or medications the morning of the test; administer 1000 µg of LT4 in the patient's usual formulation as the test dose; ensure that the patient is supervised throughout the LT4AT; perform a 4-hour test, with hourly blood samples; assay FT4; and consider that normal LT4 absorption corresponds to an FT4 increment of more than 0.40 ng/dL (5.14 pmol/L) or a TT4 increment of more than 6 μg/dL (77.23 nmol/L) for a test dose of at least 300 µg, or a percentage TT4 absorption of more than 60%. If the test indicates abnormal LT4 absorption, the physician can increase the LT4 dose, change the formulation or administration route, and/or refer the patient to a gastroenterologist.

Effect of morning versus night-time administration of proton pump inhibitor (pantoprazole) on thyroid function test in levothyroxine-treated primary hypothyroidism: a prospective cross-over study

BACKGROUND

One of the common causes of suboptimal control of thyroid stimulating hormone (TSH) in levothyroxine-treated hypothyroidism is coadministration of proton pump inhibitors (PPIs). Morning administration of pantoprazole has been shown to suppress intragastric pH to a greater extent. We therefore aimed to determine the effect of pantoprazole at different time points of the day on thyroid function test (TFT) in levothyroxine-treated overt primary hypothyroidism.

METHODS

In this single centre, hospital based, prospective, two arm cross-over study (AB, BA), participants were randomized into 2 groups based on morning (6:00 am - 7:00 am simultaneously with the scheduled levothyroxine tablet) (group M) and evening (30 min before dinner) intake of 40 mg pantoprazole tablet (group N). After the initial 6 weeks (period 1), a washout period of 1 week for pantoprazole was given, and then both the groups crossed over for another 6 weeks (period 2). Patients were instructed to continue the same brand of levothyroxine tablet at empty stomach 1-hour before breakfast. Serum TSH was measured at baseline, week 6, and week 13.

RESULTS

Data from 30 patients, who completed the study with 100% compliance, were analysed. Mean TSH values of the study participants were significantly higher both at week 6 and week 13 compared to the baseline. Mean baseline serum TSH concentrations for groups M and N were 2.70 (± 1.36), and 2.20 (± 1.06) µlU/mL, respectively. Mean serum TSH concentrations at the end periods 1 and 2 for group M were 3.78 (± 4.29), and 3.76 (± 2.77) while the levels in group N were 3.30 (± 1.90), and 4.53 (± 4.590) µlU/mL, respectively. There was a significant rise in serum TSH concentration across periods 1 and 2 in both the groups (F_{2, 58} = 3.87, p = 0.03). Within group changes in TSH across periods 1 and 2 were not statistically significant. Similarly difference in TSH between the groups, either at 6 weeks or at 13 weeks, were also not statistically significant.

CONCLUSIONS

Concomitant use of pantoprazole, even for 6 weeks, leads to significant elevation in serum TSH in levothyroxine-treated patients who are biochemically euthyroid, irrespective of timing of pantoprazole intake. Early morning and night-time administration of pantoprazole have similar effect on TFT in these patients.

A Yet Unrecognized Cause of Unusually High Levothyroxine Replacement Dose: Protein-Losing Enteropathy

Background/Objective

Large amount of protein wasting such as in nephrotic syndrome is a rare cause of high levothyroxine (LT4) replacement dose requirement. A case has been reported here that demonstrates that protein-losing enteropathy is a novel and yet unrecognized cause of high LT4 replacement dose requirement.

Case Report

A 21-year-old man with congenital heart disease was found to have primary hypothyroidism and started LT4 replacement. His weight was approximately 60 kg. Nine months later, while he was taking LT4 100 μg daily, thyroid-stimulating hormone (TSH) level was >200 μIU/mL (normal range, 0.3-4.7 μIU/mL) and free thyroxine level was 0.3 ng/dL (normal range, 0.8-1.7 ng/dL). The patient had excellent medication compliance. LT4 dose was increased to 200 μg daily and then 200 and 300 μg every other day. Two months later, TSH level was 3.1 μIU/mL and free thyroxine level was 1.1 ng/dL. He did not exhibit malabsorption or proteinuria. His albumin levels had been low since the age of 18 years (mostly <2.5 g/dL). Stool α-1-antitrypsin levels and calprotectin levels were elevated on multiple occasions. Protein-losing enteropathy was diagnosed.

Discussion

As most circulating LT4 is protein-bound, loss of protein-bound LT4 due to protein-losing enteropathy is the most plausible cause of the large LT4 dose requirement in this case.

Conclusion

This case demonstrates that protein-losing enteropathy, through loss of protein-bound thyroxine, is a novel and yet unrecognized cause of high LT4 replacement dose requirement. In patients who require high LT4 dose for unclear reasons, albumin levels should be examined and protein wasting be suspected in those with low albumin levels.

Seeking optimization of LT4 treatment in patients with differentiated thyroid cancer

Levothyroxine sodium (LT4) is the mainstay treatment to replace thyroid hormonal production in thyroidectomized patients, but, depending on the aggressiveness of the cancer and on the risk of recurrence, patients with differentiated thyroid cancer may also be treated in a TSH-suppressive or semi-suppressive mode. The pathophysiological rationale for this LT4 treatment stems from the role of TSH, considered to be a growth factor for follicular cells, potentially inducing initiation or progression of follicular cell-derived thyroid cancer. Therefore, accurate tailoring of treatment, taking into account both patient characteristics (age and comorbidities) and risk of persistent/recurrent disease, is highly recommended. Furthermore, adjustments to traditional LT4 treatment should be made in thyroidectomized patients due to the lack of thyroidal contribution to whole body triiodothyronine (T₃) concentration. Since LT4 exhibits a narrow therapeutic index and the side effects of over- and under-treatment could be deleterious, particularly in this category of patients, caution is required in dose individualization, in the mode of ingestion, and in potential pharmacological and other types of interference as well. Our aim was to analyze the current knowledge concerning LT4 dose requirements in patients with thyroid cancer according to different therapeutic approaches, taking into account a number of factors causing interference with LT4 efficacy. Specific mention is also made about the use of the novel LT4 formulations.