Diagnosis and management of treatment-refractory hypothyroidism: an expert consensus report

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.

Thyroxine overuse and clinical indices guiding successful treatment withdrawal

PURPOSE

Levothyroxine (LT4) is commonly prescribed, but there is evidence strongly suggesting that a significant proportion of these patients are on treatment without solid evidence of hypothyroidism. Small trials on treatment discontinuation, did not detect any predictors of success. Therefore, we conducted this study in an attempt to identify predicting factors for successful LT4 withdrawal.

METHODS

In 802 consecutive patients (83% females, mean age 48 ± 16 years) on LT4 treatment for 8.8 ± 7.3 years without a solid diagnosis of hypothyroidism, therapy was abruptly discontinued. A total of 387 persons were followed up for up to 4 months (group A) and 415 individuals who were euthyroid at 4 months post LT4 discontinuation, were followed up for up to 60 months (group B). Recurrent hypothyroidism was defined if thyrotropin (TSH) level exceeded 4.5mIU/L.

RESULTS

Among the entire cohort, 182 patients (23%) became hypothyroid, 40% of group A and 7% of group B (p < 0.001). The Τhyroid treatment Discrimination Index (T4RxDI), the product of TSH levels multiplied by the daily LT4 dose divided by BMI, was calculated. In group A, successful LT4 withdrawal was strongly indicated by a T4RxDI value < 2.78 (72% sensitivity, 66% specificity), while in group B, the corresponding value was 3.75 (100% sensitivity, 48% specificity).

CONCLUSIONS

Our findings reveal considerable overuse of LT4 and propose a T4RxDI product of < 3 as a valuable predictive factor of recurrent hypothyroidism, justifying a treatment discontinuation trial. If hypothyroidism does not resume within 4 months, the risk of developing long-term hypothyroidism is likely to be minimal.

Intramuscular and subcutaneous levothyroxine: success in treating refractory hypothyroidism

Introduction

Refractory hypothyroidism often poses a clinical problem, as treatment regimens are difficult to individualise to the patient and the feasibility of its delivery is difficult to organise within a healthcare system. We present a patient who became intolerant of intramuscular (IM) levothyroxine (LT4) after 18 years of treatment; thus, subcutaneous (SC) LT4 was initiated.

Case presentation

A 13-year-old female with newly diagnosed hypothyroidism remained hypothyroid despite escalating doses of oral LT4 and LT3. Thyroxine malabsorption was further suggested by nasogastric administration of LT4, whereby high-dose thyroxine administration resulted in only a 2.8 pmol/L increase in free T4 level (normal >5.14 pmol/L). She eventually achieved long-term euthyroid status at the age of 18 with fortnightly IM LT4 alongside oral LT4 and LT3. This was maintained for 18 years. Unfortunately, scar tissue developed around injection sites, resulting in increased pain and difficulty in administration. SC LT4 was trialled with success, and she has remained euthyroid for the last 6 years with self-administration and minimal side effects.

Conclusion

Refractory hypothyroidism often presents a challenge for clinicians, both for diagnosis and management. We discuss a patient with the longest follow-up to date within the published literature for both IM and SC LT4 for patient-administered treatment of refractory hypothyroidism and review the literature on alternative formulations available.

Levothyroxine Absorption Test With the Daily Levothyroxine Dose in Patients With "Refractory Hypothyroidism"

Hypothyroidism is a frequent disease, and oral levothyroxine is the mainstay of its treatment. However, more than 15% of levothyroxine-treated patients fail to achieve the recommended serum TSH level, and "refractory hypothyroidism" is due to either malabsorption, increased metabolism of thyroxine, or nonadherence to treatment. A levothyroxine absorption test must be used to differentiate true malabsorption from nonadherence or pseudo-malabsorption. We analyzed 166 levothyroxine absorption tests in 143 hypothyroid patients (109 women, mean age 43 ± 1 years) treated with oral levothyroxine. Despite a daily dose of 3.26 ± 0.09 g/kg/day, mean serum TSH concentration was 25.7 ± 3.7 mU/L. "Refractory hypothyroidism" was in the context of gastritis (24%), Helicobacter pylori infection (18%), drug interference with levothyroxine absorption (15.6%), nonadherence to treatment (10%), celiac disease (2.5%), or bariatric surgery (1.2%). After an overnight fast, patients orally took their daily dose of levothyroxine (220 ± 6 g), and blood samples were drawn before levothyroxine intake and every 2 hours for 24 hours. After levothyroxine intake, the mean total (basal = 7.64 ± 0.26 g/dL, peak 9.41 ± 0.28 g/dL), and free (basal = 12.58 ± 0.42 pg/mL, peak 15.77 ± 0.51 pg/mL) T4 levels increased (P < .001), total and free T4 peaks were observed at 4.2 ± 0.23 and 4.30 ± 9.27 hours, respectively. Levothyroxine absorption tests were well tolerated. In conclusion, in most patients with "refractory hypothyroidism," this clinical study revealed that the levothyroxine absorption test can be achieved via the absorption of the daily dosage of levothyroxine, and the evaluation of total or free T4 concentrations over 4- or 6-hour follow-up. The test is well tolerated without cardiovascular adverse events.

The association between primary frozen shoulder and serum lipids may be overestimated: evidence based on retrospective observational studies and Mendelian randomization

Background

Previous studies have shown that dyslipidemia is significantly associated with primary frozen shoulder and may be a risk factor for the development of primary frozen shoulder. However, these findings may be biased by a number of confounding factors. We investigated the association between serum lipids and primary frozen shoulder by retrospective analysis and two-sample Mendelian randomization (MR) methods.

Methods

This retrospective observational study included 284 patients with primary frozen shoulder diagnosed from October 2020 to October 2023 at four centers as the experimental group. Patients with diabetes and thyroid dysfunction were excluded. The control group consisted of age- and sex-matched people who underwent a health checkup. We compared total cholesterol (TC), triglycerides (TG), high-density lipoprotein (HDL), and low-density lipoprotein (LDL) between the two groups. Genetic variants for the serum lipids and frozen shoulder were then extracted from large-scale genome-wide association studies. Causal effects were assessed using Inverse variance weighting (IVW), Weighted median, MR-Egger, simple and weighted models in MR analysis.

Results

The analysis showed that after excluding patients with diabetes and thyroid dysfunction, the serum lipids (TC, TG, HDL, and LDL) in the primary frozen shoulder group were no different from those of normal individuals. None of the MR methods found significant causal evidence between them.

Conclusions

Dyslipidemia in patients with primary frozen shoulder may be influenced by confounding factors such as diabetes and thyroid dysfunction. These findings deepen our understanding of primary frozen shoulder risk factors.

Macro-Thyrotropin Syndrome: Prevalence and Clinical Profile of an Under-Recognised Rare Entity in Thyroidology

Introduction

Macro-thyrotropin syndrome (macro-TSH) is a rare condition characterised by the formation of a complex between thyroid-stimulating hormone (TSH) and an unknown component, resulting in elevated TSH levels that do not accurately reflect thyroid status. This study aimed to investigate the prevalence and clinical profile of macro-TSH among patients with subclinical hypothyroidism (SCH).

Methods

A total of 1500 patients were evaluated, with 135 exhibiting elevated TSH levels (>10 IU/mL) and normal free-thyroxine levels. Macro-TSH was diagnosed based on persistent elevated TSH levels despite serial dilutions and confirmed by less than 60% TSH recovery following polyethylene glycol (PEG) precipitation.

Results

Finally, 115 were diagnosed with SCH, 15 with macro-TSH, and 1245 were categorised into non-thyroid groups. The prevalence of macro-TSH, SCH, and heterophilic antibodies interfering with immunoassay was 1.09%, 8.36%, and 0.36%, respectively. Among macro-TSH patients, 13.33% exhibited classical hypothyroid features, contrasting with the 52.0% observed in SCH patients. Female gender and a family history of hypothyroidism were associated with higher odds of having macro-TSH. Diabetes mellitus, clinical symptoms of hypothyroidism (except lethargy), higher TSH level, and post-PEG TSH recovery were significantly associated with SCH compared to macro-TSH. The mean TSH level was five times higher in macro-TSH compared to SCH.

Conclusion

Macro-TSH syndrome represents a distinct clinical entity within the spectrum of SCH, characterised by disproportionately high TSH levels. Recognising macro-TSH is crucial for accurate diagnosis and appropriate management of SCH.

Levothyroxine malabsorption following sleeve gastrectomy

Summary

Oral levothyroxine (LT4) is prescribed worldwide for hypothyroidism. Bariatric surgery for patients with obesity has shown a substantial, long-term weight loss and considerable improvement of obesity-related diseases. LT4 malabsorption represents a significant cause of refractory hypothyroidism, well known after malabsorptive bariatric surgery such as Roux-en-Y gastric bypass. However, few studies have shown an increase in oral LT4 needed after sleeve gastrectomy. We present a 47-year-old woman with class III obesity and a history of papillary thyroid cancer, with an excellent biochemical and structural response after total thyroidectomy and radioactive iodine. She underwent sleeve gastrectomy 3 years later and developed refractory hypothyroidism despite taking high doses of oral LT4 and ensuring compliance. The T4 absorption test confirmed gastrointestinal LT4 malabsorption. She was initiated on intramuscular LT4 and oral T3 (liothyronine) with improving symptoms and levels of thyroid-stimulating hormone.

Learning points

Monitoring thyroid function tests is essential after bariatric surgery, including sleeve gastrectomy. Oral LT4 malabsorption should be considered in cases of refractory hypothyroidism. The T4 absorption test is a useful tool for distinguishing true malabsorption from pseudo-malabsorption. Decreased LT4 absorption after bariatric surgery might be explained by higher gastric pH and reduced stomach volume (impaired dissolution) and by interference with food, vitamin/mineral supplements or other drugs. When LT4 malabsorption is confirmed, a trial of other oral formulations (LT4 tablet crushed, soft gel or liquid preparation) or parenteral administrations is suggested.

Refractory hypothyroidism in children: an overview

Refractory hypothyroidism (RF) defined as raised serum levels of thyroid stimulating hormone (TSH) above upper limit of the reference range with or without the persistence of hypothyroid symptoms following a 6-week interval after the dosage was last increased to upper limits of dose per age. The most common cause of RH is inadequate compliance. In addition, diet, concomitant medication interactions, and gastrointestinal diseases can all result in l-thyroxine (LT4) malabsorption, which can cause RH. Moreover, weight gain, switching brands of LT4, poor storage of LT4, chronic liver disorders, cystic fibrosis, nephrotic syndrome, consumptive hypothyroidism, Addison's disease are significant contributors to RF in children. RH in children is frequently asymptomatic, when symptoms do occur, they are typically minor and resemble those of hypothyroidism. It is essential to identify RH early and treat its underlying cause in order to avoid overusing LT4, which can lead to cardiac and bone problems. Endocrinologists should handle children who they suspect of having RH methodically after making sure there is enough compliance. Searching for undiagnosed illnesses and/or other factors that can affect LT4 absorption could be part of this. We present this review after an extensive literature search and long-standing clinical experience. This review's objective is to shed light on the causes, clinical manifestations, investigations, and treatment of RH in children.

Rapid supervised levothyroxine absorption test in refractory hypothyroidism: suggestion for assessing absorption using two blood samples in low-resource settings

Refractory hypothyroidism is associated with high morbidity and increased healthcare expenditure. In general, the use of the levothyroxine absorption test looks promising in evaluating refractory hypothyroidism but has shown significant variability in protocols in multiple settings. We intended to assess the usefulness of the levothyroxine absorption test in a low-resource setting and to assess the factors associated with refractory hypothyroidism. A cross-sectional study among age-matched 25 cases of refractory hypothyroidism and 24 treatment-responsive hypothyroid controls was conducted. A supervised levothyroxine absorption test was performed with levothyroxine 1000 μg tablets after a 10-h fast, and serum free tetraiodothyronine (FT4) levels were measured at 0, 1, 2, 3, 4, and 5 h. Descriptive statistics, chi-square test, Student's t-test, and logistic regression were used in the analysis. Results showed no significant difference in age, body weight, etiology of hypothyroidism, interfering medications, thyroxine storage, and ingestion technique in cases and controls. Cases had a longer duration of hypothyroidism and males had a higher peak FT4 concentration. During pooled analysis, serum FT4 peaked at 3 h with an increment of 149.4% (128.4-170.5%) from baseline and plateaued thereafter. The absolute value of FT4 at 3 h was 41.59 (s.d. 14.14) pmol/L (3.23 ng/dL). We concluded that there was no significant difference in the pattern of levothyroxine absorption in both groups. The most common cause of refractory disease was pseudo-malabsorption. Rapid supervised levothyroxine absorption test with two blood samples for FT4 at baseline and at the peak of absorption (3 h) is simple, convenient, and cost-effective, particularly in low-resource settings.

Liquid L-T4 therapy in hypothyroid patients with gastric diseases, an observational study

Introduction

This is an observational and retrospective study, in which we have analyzed data from patients affected by gastric diseases (p) who have been treated with liquid L-T4 (L-LT4;84 p), or tablet L-T4 (T-LT4;120 p), for the replacement therapy of hypothyroidism. The aim of the study is to compare the stability of TSH [normal range, 0.3-3.5 μIU/ml] in these patients.

Methods

All p assumed L-T4 30 minutes before breakfast. The types of gastric disease were: a) T-LT4 group: 74 chronic gastritis (CG); 4 gastrectomy for gastric cancer (GTx); 42 gastro-plastics (GP); b) L-LT4 group: 60 CG; 3 GTx; 21 GP (p>0.05). 66% p in T-LT4 group were chronically treated with proton pump inhibitors (PPI), against 51% in L-LT4 group (p>0.05). The frequency of Helicobacter Pylori infection was 17% in both T-LT4 and L-LT4 groups. The gender distribution, mean age and body weight were similar in the 2 groups (p>0.05). The mean L-T4 dosage in T-LT4 group at the basal evaluation was 1.22+/-0.27 μg/kg/die, in the L-LT4 group 1.36+/-0.22 μg/kg/die (p>0.05).

Results

At the basal evaluation the prevalence of patients with a TSH>3.5 μIU/mL in T-LT4 group was 36%, in L-LT4 group 46% (p<0.05). After adjustment of the dosage of the LT-4 therapy, the p were re-evaluated in an interval range of 5-9 months, for 4 times, during an overall period ranging from 23 to 31 months. At the first re-evaluation, the prevalence of p with a TSH>3.5 μIU/mL was 13% in both groups. At the second re-evaluation, the prevalence of p with a TSH>3.5 μIU/mL in T-LT4 group was 26%, in L-LT4 group 13% (p>0.05). At the third re-evaluation, the prevalence of p with TSH<3.5 μIU/mL in T-LT4 group was 19%, in L-LT4 group 9% (p=0.05). At the fourth and last re-evaluation, the prevalence of patients with a TSH>3.5 μIU/mL in T-LT4 group was 18%, in L-LT4 group 5% (p<0.05). Mean FT4 and FT3 circulating levels were not significantly different in the two group at each visit.

Discussion

These data suggest that the liquid L-T4 formulation therapy can result in a more stable control of TSH levels in hypothyroid patients with gastric disorders in the long-term follow-up.

Proton Pump Inhibitors Do Not Affect the Bioavailability of a Novel Liquid Formulation of Levothyroxine

OBJECTIVE

This study evaluates the impact of a representative proton pump inhibitor (PPI) (omeprazole), administered simultaneously or staggered, on the pharmacokinetics of levothyroxine (LT4) solution (Tirosint-SOL).

METHODS

This was a randomized, 3-way crossover, comparative bioavailability study in 36 healthy adults under fasting conditions. Omeprazole 40 mg delayed-release capsule was administered once daily from Day 1 to 6 (mornings, Treatment-A; evenings, Treatment-B; none, Treatment-C) to increase and stabilize gastric pH. In the morning of Day 5, a single dose of LT4 solution 600 mcg was administered. Blood samples were collected 0 to 48 hours post-LT4 administration. Noncompartmental pharmacokinetic parameters were calculated for total serum thyroxine using baseline-corrected data. Maximum concentration (Cmax) and area under the concentration-time curve (AUC0-48) were included in an analysis of variance to obtain geometric mean ratios and 90% confidence intervals.

RESULTS

For both comparisons (A/C and B/C), geometric mean ratios and 90% confidence intervals for all parameters were within the equivalence boundaries (80%-125%), indicating bioequivalence: for A/C, AUC0-48 98.98% [94%-104%], and Cmax 91.68% [87%-97%]; for B/C, AUC0-48 98.94% [95%-103%], and Cmax 94.90% [90%-100%]. Median Tmax (time associated with Cmax) was similar across treatments.

CONCLUSION

This study demonstrated that Tirosint-SOL bioavailability is unaffected by coadministration of a representative PPI, given simultaneously or staggered by about 12 hours, compared to administration of LT4 solution alone. For hypothyroid patients on PPI therapy, administration of LT4 solution may reduce variations in thyroid stimulating hormone levels related to intermittent use of acid-reducing drugs and consequently the need for dose adjustments.

Liquid Thyroxine Improves Outcomes in Hypothyroid Patients With Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome

OBJECTIVE

Malabsorption of levothyroxine (LT4) is often seen in patients with hypothyroidism and gastrointestinal (GI) conditions. Our study was designed to establish the prevalence of small intestinal bacterial overgrowth (SIBO) in patients with hypothyroidism and irritable bowel syndrome (IBS), and to demonstrate that liquid LT4 is more consistently absorbed vs tablet, leading to improvement in thyroid and GI symptoms.

METHODS

This was a single-center, open label, prospective cohort study of liquid LT4 in 75 adult patients with hypothyroidism and IBS. Patients were transitioned from LT4 tablets to solution at equivalent dosing. Patients returned at 6 and 12 weeks for repeat thyroid levels and completion of validated questionnaires. A standard 2-hour SIBO breath test was administered at Week 6. Patients recorded daily stool appearance and frequency.

RESULTS

Prevalence of SIBO was 65.3%. Liquid LT4 normalized thyroid stimulating hormone (TSH) in a higher percentage of patients vs tablet (77.55% vs 57.14%); significantly decreased TSH in subjects with SIBO; improved hypothyroid symptoms, IBS symptoms, stool appearance in all groups, and significantly altered bowel frequency among those with SIBO.

CONCLUSION

Small intestinal bacterial overgrowth (SIBO) is common in patients with hypothyroidism and IBS. Among SIBO patients, LT4 tablets were inefficiently absorbed, leading to suboptimal thyroid control; however, transitioning from LT4 tablets to solution normalized TSH and improved hypothyroid symptoms. Liquid LT4 also significantly improved GI symptoms in all patients with hypothyroidism and IBS, regardless of SIBO status. Additionally, 1 in 5 patients had complete resolution of IBS symptoms after switching from LT4 tablets to solution, independent of changes in TSH.

Analysis of dose-TSH response effect of levothyroxine soft-gel formulation

Background

Hypothyroidism is treated with daily levothyroxine (LT4). In recent years, soft gel caps of LT4 (LT4-C) have been commercialized, and their performance has been optimized. Since guidelines recommend dose LT4 according to the tablet preparation efficacy, the present study was undertaken to obtain data about the daily requirement, normalized per body weight, of LT4-C.

Methods

Patients undergoing LT4-C after total thyroidectomy and radioiodine treatment for differentiated thyroid carcinoma were selected. There was no specific indication of suppression of TSH (i.e., <0.5 or <0.1 mIU/L). Patients were required to maintain a stable LT4 dose during the study period. Patients with interfering factors were excluded from this study.

Results

Thirty patients were enrolled (18 females and 12 males; median age, 50 years; median body weight, 71 kg; median LT4-C dose, 1.71 µg/kg/day). The analysis of patient age did not reveal any differences. The LT4-C dose correlated with free-T4 p = 0.03), but not with TSH (p = 0.42) and free-T3 (p = 0.13). TSH was <1.0 mIU/L in 90% of the cases. The LT4-C dose-TSH response effect was analysed by probit regression model: the probability to achieve TSH <1.0 mIU/l was 99% with a dose of 1.84 (95%CI 1.57-2.12) µg/kg/day, 75% with a dose of 1.38 µg/kg/day (95%CI 1.17-1.59), and 50% with a dose of 1.20 (95%CI 0.96-1.43). At ROC curve analysis, the most accurate cut-off of LT4-C dose to achieve TSH <1.0 mIU/l was 1.53 ug/kg/day with 70% sensitivity and 100% specificity.

Conclusions

Athyreotic patients can be initially treated with an LT4-C dose lower than previously stated. Therefore, further prospective studies are warranted.

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.

Levothyroxine liquid oral substitution as an alternative treatment for refractory hypothyroidism due to gastrointestinal malabsorption: A case report

Tablets of levothyroxine (LT4) are the most used form for the treatment of hypothyroidism. Some patients may present with refractory hypothyroidism despite a high daily LT4 dose. We report the case of a 49-year-old woman who was admitted to our department for refractory hypothyroidism. She was treated with 300 μg oral LT4 tablets daily (3.9 μg/kg/day). Despite good compliance and regular intake of high doses of LT4, she had persistent symptoms of hypothyroidism and a thyroid-stimulating hormone level of 92.4 mIU/L. LT4 absorption test was consistent with the diagnosis of malabsorption. Etiological investigations revealed Helicobacter pylori gastritis. Helicobacter infection was adequately treated, but symptoms of hypothyroidism and elevated thyroid-stimulating hormone persisted. Increased LT4 doses (400 μg) failed to normalize thyroid-stimulating hormone levels. Thus, she was put on LT4 liquid form at a dose of 80 drops/day per day (400 µg). Two weeks later, she presented with clinical and biological improvement with a normal free thyroxine level of 1.14 ng/dL. Patients with gastrointestinal disorders may present with refractory hypothyroidism despite increasing doses of LT4. Switching to liquid formulation may resolve this problem.

Validity of the Rapid Thyroxine Absorption Test for the Differentiation Between Levothyroxine Non-compliance and Malabsorption in Thyroid-Stimulating Hormone Refractory Hypothyroidism

Introduction Thyroid-stimulating hormone refractory hypothyroidism is a common problem. This is due to either non-compliance or malabsorption with levothyroxine (LT4). The study aimed to assess the validity of the rapid LT4 absorption test in the differentiation between LT4 malabsorption and non-compliance. Methods A cross-sectional study was done from January to October 2022 at Faiha Specialized Diabetes, Endocrine, and Metabolism Center, in Basrah, Southern Iraq. Twenty-two patients with thyroid-stimulating hormone (TSH) refractory hypothyroidism were evaluated by rapid LT4 absorption test with measurements of TSH before 1000 μg LT4 intake, and free thyroxine (pmol/l) and total thyroxine before (nmol/l) (baseline TT4 and baseline FT4) and two hours after (2-HR TT4 and 2-HR FT4). The findings were compared with the following four-week-long supervised LT4 absorption test results. Results In the rapid LT4 absorption test, patients with (2-HR FT4 minus baseline FT4 ≤1.28 pmol/l (0.1 ng/dl) or 2-HR FT4 minus baseline FT4 1.28-6.43 pmol/l (0.1-0.5 ng/dl) plus 2-HR TT4 minus baseline TT4<72.08 nmol/l (5.6 µg/dl)), eight out of 10 patients were correctly diagnosed with malabsorption. And in those with (2-HR FT4 minus baseline FT4 ≥6.43 (0.5 ng/dl) or 2-HR FT4 minus baseline FT4 1.28-6.43 (0.1-0.5 ng/dl) plus 2-HR TT4 minus baseline TT4≥72.08 (5.6 µg/dl)), 11 out of 12 patients were correctly diagnosed as non-compliant. This criterion showed 88.8% sensitivity, 15.4% specificity, 80% positive predictive value, and 91.6% negative predictive value for diagnosing LT4 malabsorption. Conclusion The rapid LT4 absorption test showed good diagnostic accuracy in differentiating non-compliance from malabsorption when (2-HR FT4 minus baseline FT4) and (2-HR TT4 minus baseline TT4) were used as criteria.

Levothyroxine malabsorption or pseudomalabsorption? A question in the management of refractory hypothyroidism

PURPOSE

The levothyroxine absorption test (LT4AT) is an important tool for distinguishing hypothyroidism due to malabsorption from 'pseudomalabsorption' conditions. Our aim was to review our institution's LT4AT results and assess its role in the management of patients with refractory hypothyroidism.

METHODS

We performed a retrospective study of all patients evaluated for refractory hypothyroidism who underwent LT4AT in our tertiary center between 2014 and 2020. Its results and the impact on thyroid function management during follow-up were assessed.

RESULTS

Ten female patients were included with a mean age of 40 years (min-max: 26-62). Mean weight was 72 kg (min-max: 43-88) and baseline LT4 dosage ranged from 2.5 to 5.3 µg/kg/day. The most common causes of hypothyroidism were postsurgical in 50% (n = 5) and autoimmune in 20% (n = 2). During LT4AT, normal LT4 absorption was found in all but one individual (mean FT4 increase of 231%, min-max: 85-668). The only patient with objective LT4 absorption impairment (maximal increase of 48% by hour 5) presented also Helicobacter pylori gastritis and prior history of 'intestinal surgery' during childhood. No adverse events were reported during any of the LT4ATs. During follow-up (median 11.5 months (IQR 23)), three patients obtained euthyroidism and six had improved their hypothyroidism state.

CONCLUSIONS

The LT4AT is an effective and safe way to assess refractory hypothyroidism and provides valuable information to distinguish LT4 malabsorption from 'pseudomalabsorption'. Our data suggest that most patients with suspicious LT4 malabsorption perform normally during LT4AT. This test provides relevant information for better management of patients with refractory hypothyroidism.

Approach to adult patients with primary hypothyroidism in some special situations: a position statement from the Thyroid Department of the Brazilian Society of Endocrinology and Metabolism (SBEM)

Primary hypothyroidism is a common disorder in clinical practice. The management of most cases of hypothyroidism is usually straightforward, but the best approach in some special situations may raise questions among physicians. This position statement was prepared by experts from the Brazilian Society of Endocrinology and Metabolism to guide the management of three special situations, namely, hypothyroidism in the elderly, subclinical hypothyroidism in patients with heart disease, and difficult-to-control hypothyroidism. The authors prepared the present statement after conducting a search on the databases MEDLINE/PubMed, LILACS, and SciELO and selecting articles with the best evidence quality addressing the selected situations. The statement presents information about the current approach to patients in these special situations.

Primary hypothyroidism resolves after switching from L-thyroxine solid tablets to liquid oral substitution. A rare case without evidence of an underlying gastrointestinal malabsorption syndrome

A case of refractory primary hypothyroidism is presented. Despite laboratory-guided hormonal substitution, the patient remained hypothyroid. Multiple diagnostic tests ruled out all known causes of levothyroxine malabsorption. Interestingly, clinical and laboratory responding was promptly achieved, after switching the application format from solid tablets to liquid formula.

SEVERE REFRACTORY HYPOTHYROIDISM IN A 48-YEAR-OLD FEMALE: ROLE OF LOW-DOSE THYROXINE ABSORPTION TEST IN ESTABLISHING DIAGNOSIS OF NONCOMPLIANCE

A 48-year-old female presented with severe chronic hypothyroidism despite progressively increasing doses of levothyroxine. Poor adherence was suspected based on previous laboratory investigations. A low dose thyroxine absorption test using 400 µg of levothyroxine taken orally was performed. FT4 increased by 4.7 pmol/L at 3 hours and 6.6 pmol/L at 5 hours, following ingestion, effectively ruling out malabsorption. Her cardiac hemodynamic profile, measured noninvasively, also improved following levothyroxine intake, further supporting our diagnosis. Poor adherence was successfully managed by implementing twice weekly visits by a registered nurse and an improvement in both thyroid function tests and cardiac parameters was seen at the one-month follow-up visit. We suggest using a lower dose thyroxine absorption test, owing to its efficacy in establishing diagnosis and a safer alternative compared to higher doses in particular in high-risk cardiac patients.

Levothyroxine treatment and gastric juice pH in humans: the proof of concept

PURPOSE

Despite the absorption of oral thyroxine (T4) occurs in the small bowel, several patients with gastric disorders show an increased need for T4. In vitro evidence suggested that medium pH variations interfere with T4 dissolution. This study was aimed at finding the proof of concept of a direct relationship between the minimal effective dose of T4 and the actual gastric juice pH.

PATIENTS AND METHODS

Among 311 consecutively thyroxine-treated patients, 61 bearing Hashimoto's thyroiditis (52 F/9 M; median age = 51 years) who complained persistent dyspepsia and/or upper abdominal symptoms following a noninvasive workup for gastrointestinal disorders, underwent EGDS with multiple biopsies and gastric juice pH measurement. All patients accepted to take thyroxine in fasting conditions, abstaining from eating or drinking for one hour.

RESULTS

Thyroxine requirement increased along with the rising gastric pH (ρ = 0.4229; p = 0.0007). A multivariate analysis revealed that gastric pH was, beside body mass index, the far more important independent variable in determining the effective dose of T4 (p = 0.001). The ROC curve revealed that the pH threshold for an increased thyroxine requirement was at 2.28, being the AUC by 78%. Subdividing patients by the histologic findings, it appeared a significant increase (p = 0.0025) along with the progressive damage of gastric mucosa.

CONCLUSION

The in vivo measurement of gastric pH highlighted its key role in determining the minimal effective dose of oral T4 and may explain the interference of food, of some drugs and gut disorders on levothyroxine treatment.

Determining the Association Between Helicobacter pylori Infection and Treatment-Refractory Hypothyroidism

Introduction

Refractory hypothyroidism, despite weight-based thyroxine dosing, is a common endocrinology consultation in outpatients. Chronic Helicobacter (H.) pylori infection has been reported to be responsible for the poor absorption of thyroxine from the small gut leading to suboptimal response with contradictory evidence. This study was carried out to determine the association of chronic Helicobacter pylori infection with refractory hypothyroidism in outpatients presenting to a tertiary care hospital.

Methods

One hundred thirty patients with the diagnosis of hypothyroidism, visiting Jinnah Allama Iqbal Institute of Diabetes and Endocrinology (JAIDE) Jinnah Hospital Lahore, Pakistan, from January 2020 to February 2021, were included in the study after informed consent following the non-probability consecutive sampling technique. All of these patients were 15-70 years of age, non-pregnant, and receiving thyroxine treatment for at least six weeks. Patients with a history of gastric surgery, malabsorption syndrome, or poor compliance were excluded from the study. Patients’ age, sex, and body mass index (BMI) were recorded in a structured proforma. Patients were categorized into two groups, i.e. controls (biochemically euthyroid on thyroxine treatment with TSH < 4.5mU/L) and cases (refractory hypothyroidism despite 1.6 mcg/kg thyroxine treatment with TSH > 4.5 mU/L). The presence of chronic H. pylori infection was checked with serum immunoglobulin G (IgG) testing by enzyme-linked immunoassay (ELISA) from the hospital laboratory and data analysis was done by SPSS version 21.0 (IBM Corp., Armonk, NY).

Results

One hundred thirty patients were included in this study, with an age range from 15 to 70 years. Of these, 65/130 (50%) were euthyroid on treatment and 65/130 (50%) had treatment-refractory hypothyroidism. The mean age of patients in our study was 45.81 ± 11 years, with 118 (90.8%) female patients. The prevalence of positive H. pylori IgG antibody was 47/130 (36.2%) overall, with 23 patients (35.4%) in the control (euthyroid) group and 24 patients (36.9%) in the cases (refractory hypothyroidism) group. The difference between the two groups was not statistically significant with an odds ratio of 1.069 (CI 0.523 - 2.187) and a p-value of 0.855. Moreover, age, gender, and BMI had no effect on chronic H. pylori association with refractory hypothyroidism.

Conclusion

This study does not suggest any significant association between chronic H. pylori infection and treatment-refractory hypothyroidism. Other factors like poor compliance, drug-drug interactions, and malabsorption disorders should be preferably sought in case of refractory hypothyroidism.

An Overview on Different L-Thyroxine (l-T4) Formulations and Factors Potentially Influencing the Treatment of Congenital Hypothyroidism During the First 3 Years of Life

Congenital hypothyroidism (CH) is a relatively frequent congenital endocrine disorder, caused by defective production of thyroid hormones (THs) at birth. Because THs are essential for the development of normal neuronal networks, CH is also a common preventable cause of irreversible intellectual disability (ID) in children. Prolonged hypothyroidism, particularly during the THs-dependent processes of brain development in the first years of life, due to delays in diagnosis, inadequate timing and dosing of levothyroxine (l-thyroxine or l-T₄), the non-compliance of families, incorrect follow-up and the interference of foods, drugs and medications affecting the absorption of l-T₄, may be responsible for more severe ID. In this review we evaluate the main factors influencing levels of THs and the absorption of l-T₄ in order to provide a practical guide, based on the existing literature, to allow optimal follow-up for these patients.

Kisspeptin treatment improves fetal-placental development and blocks placental oxidative damage caused by maternal hypothyroidism in an experimental rat model

Maternal hypothyroidism is associated with fetal growth restriction, placental dysfunction, and reduced kisspeptin/Kiss1R at the maternal-fetal interface. Kisspeptin affects trophoblastic migration and has antioxidant and immunomodulatory activities. This study aimed to evaluate the therapeutic potential of kisspeptin in the fetal-placental dysfunction of hypothyroid Wistar rats. Hypothyroidism was induced by daily administration of propylthiouracil. Kisspeptin-10 (Kp-10) treatment was performed every other day or daily beginning on day 8 of gestation. Feto-placental development, placental histomorphometry, and expression levels of growth factors (VEGF, PLGF, IGF1, IGF2, and GLUT1), hormonal (Dio2) and inflammatory mediators (TNFα, IL10, and IL6), markers of hypoxia (HIF1α) and oxidative damage (8-OHdG), antioxidant enzymes (SOD1, Cat, and GPx1), and endoplasmic reticulum stress mediators (ATF4, GRP78, and CHOP) were evaluated on day 18 of gestation. Daily treatment with Kp-10 increased free T3 and T4 levels and improved fetal weight. Both treatments reestablished the glycogen cell population in the junctional zone. Daily treatment with Kp-10 increased the gene expression levels of Plgf, Igf1, and Glut1 in the placenta of hypothyroid animals, in addition to blocking the increase in 8-OHdG and increasing protein and/or mRNA expression levels of SOD1, Cat, and GPx1. Daily treatment with Kp-10 did not alter the higher protein expression levels of VEGF, HIF1α, IL10, GRP78, and CHOP caused by hypothyroidism in the junctional zone compared to control, nor the lower expression of Dio2 caused by hypothyroidism. However, in the labyrinth zone, this treatment restored the expression of VEGF and IL10 and reduced the GRP78 and CHOP immunostaining. These findings demonstrate that daily treatment with Kp-10 improves fetal development and placental morphology in hypothyroid rats, blocks placental oxidative damage, and increases the expression of growth factors and antioxidant enzymes in the placenta.

Weekly Versus Daily Levothyroxine Tablet Replacement in Adults with Hypothyroidism: A Meta-Analysis

Objectives

Daily levothyroxine is the treatment of choice and standard of care in hypothyroidism, sufficient to restore thyroid stimulating hormone (TSH) to normal range. For many patients, daily lifelong therapy is required, making adherence a major issue. In such cases, weekly replacement may be a suitable alternative to improve adherence. In this study, we aimed to determine the efficacy and safety of weekly levothyroxine replacement among adults with hypothyroidism.

Methodology

Electronic databases were searched. Two reviewers (HCC and RBL) independently screened the abstracts, reviewed full-text papers, critically appraised the quality of included studies using PRISMA guidelines. Meta-analysis was performed using the random-effects model. The primary outcome is the difference in serum TSH levels between weekly and daily administration, while secondary outcomes included adverse events and symptoms of hypothyroidism.

Results

The primary outcome is the difference in serum TSH levels between weekly and daily administration. Secondary outcomes included adverse events and clinical symptoms. The study included two randomized trials (n=109) in the primary analysis. The difference in TSH levels was 1.78 mIU/mL higher [(95% confidence interval (CI): 1.28 to 2.28, p<0.00001] at 6 weeks and 1.22 mIU/mL higher (95% CI: 0.76 to 1.67, p<0.00001) at 12 weeks for the weekly regimen. There was no significant heterogeneity between the two groups. There was no significant difference in hypothyroid symptoms and adverse events before and after levothyroxine treatment within each group.

Conclusions

Weekly levothyroxine resulted in less suppression and higher mean serum TSH levels, while still remaining within the normal reference range. It may be a suitable alternative for non-adherent patients. However, larger randomized trials with longer duration of follow-up are needed to firmly establish its role.

Triiodothyronine alongside levothyroxine in the management of hypothyroidism?

The current guideline-based management of hypothyroidism recommends monotherapy with levothyroxine (LT4), titrated to maintain the level of thyrotropin within a euthyroid reference range. This has been successful for most people with hypothyroidism, but a substantial minority still report symptoms of hypothyroidism unexplained by a comorbid medical condition. LT4 is essentially a prodrug for triiodothyronine (T3), the thyroid hormone that acts on target tissues in the brain and the periphery. Thyroid hormone replacement with LT4 alone does not restore physiological tissue levels of thyroid hormones, particularly T3. During the last two decades, much interest has focussed on the potential of combinations of LT4 and T3 to provide a superior outcome to LT4 monotherapy for people with hypothyroidism, especially those with residual symptoms despite thyrotropin-optimized LT4. This review seeks to provide an overview of currently available evidence on combination (LT4 + T3) therapy to be used for personalized medicine in patients with hypothyroidism. A number of randomized, controlled trials (RCTs) have failed to demonstrate superiority for the combination therapy approach, largely due to non-physiological T3 doses. However, patients with hypothyroidism are highly heterogeneous in terms of their residual thyroid function, individual set points for optimal thyroid homeostasis and for the presence or absence of polymorphisms in deiodinase enzymes in tissues that activate and deactivate circulating thyroid hormones. Accordingly, these RCTs may have failed to demonstrate benefits of combination therapy in individual hypothyroid phenotypes. The pharmacokinetics of LT4 and T3 also differ, which is a barrier to their co-administration. Future clinical trials using LT4 + T3 tablets better suited for combination therapy will resolve the outstanding research questions relating to the place of LT4 + T3 combination therapy in the management of hypothyroidism.

Precision Medicine in Autoimmune Thyroiditis and Hypothyroidism

Autoimmune thyroid diseases (AITD) are T-cell-mediated organ specific autoimmune disorders, deriving from an altered response of the immune system that leads to the immune attack to the thyroid. Hashimoto’s thyroiditis (HT) and Graves’ disease (GD) are the two principal AITD clinical presentations. Hypothyroidism and thyrotoxicosis are, respectively, the clinical hallmarks of HT and GD. Patients with autoimmune thyroiditis are treated daily with synthetic L-thyroxine (L-T4) at the dose of 1.5–1.7 μg/kg. Various L-T4 formulations are commercially available (tablet, liquid solution, or soft gel capsule). L-T4 in tablets is generally prescribed to treat hypothyroidism, whereas the liquid formulation, or soft gel capsules, can be administered in hypothyroid patients in case of malabsorption or in patients in therapy with drugs interfering with L-T4 absorption. Furthermore, myoinositol has a crucial role in thyroid autoimmunity and function. Clinical studies reported a significant decline in TSH and antithyroid autoantibodies levels after treatment with myoinositol + selenium in patients with subclinical hypothyroidism and autoimmune thyroiditis. Moreover, thyroidectomy can be rarely recommended in patients with autoimmune thyroiditis, with cosmetic reasons for a goiter, or with important signs or symptoms of local compression, or nodular disease with a “suspicious” cytology for malignancy. Furthermore, a recent randomized trial suggested that total thyroidectomy can improve quality of life and fatigue, while medical therapy did not. In this review, we overview currently available evidence in personalized medicine in patients with autoimmune thyroiditis and hypothyroidism. Further research is needed in larger population to investigate the effect of these new treatments on quality of life.

Subcutaneous administration of levothyroxine: a novel approach to refractory hypothyroidism - A review and a case report

Treatment-refractory hypothyroidism is a common clinical finding. Substantial causes include poor compliance and intake failure as well as gastrointestinal diseases, such as inflammatory bowel disease and short bowel syndromes. Increasing oral dosage of levothyroxine (LT4) is not always effective. Therefore, alternative routes of administration are necessary. In this report, we evaluate alternative treatment modalities for refractory hypothyroidism and present a 28-year-old woman with intestinal drug malabsorption successfully treated by subcutaneous LT4 administration. In this patient, a parenteral form of LT4, 500 μg/5 ml, was administered subcutaneously in a split dosage regimen. Blood hormone levels returned to normal within a few days and remained stable over an 8-month follow-up period.

Levothyroxine Sodium Oral Solution Normalizes Thyroid Function in a Patient with Hashimoto's Disease, Gastritis, Diabetic Gastroparesis, and Small Intestinal Bacterial Overgrowth (SIBO)

BACKGROUND

Levothyroxine (L-T4) is used as a standard-of-care treatment in patients with hypothyroidism. L-T4 is absorbed throughout the small intestine, and consistent drug absorption is required for successful treatment. Patients with Hashimoto's disease (autoimmune thyroiditis) often have food and medication sensitivities, as well as comorbid gastrointestinal (GI) disorders detrimental to L-T4 absorption.

CASE PRESENTATION

This case report describes a 51-year-old female patient with long-standing Hashimoto's disease and multiple sensitivities to food chemicals and medications. The patient suffered from GI symptoms and poor thyroid-stimulating hormone (TSH) control. She was switched to compounded thyroxine/triiodothyronine medication due to her multiple allergies, with only mild improvement in thyroid function and no symptom resolution. She was subsequently diagnosed with gastroparesis and small intestinal bacterial overgrowth (SIBO). Because of further worsening of her GI symptoms and weight loss, she was switched to levothyroxine sodium oral solution (Tirosint®-SOL), which contains only three ingredients-levothyroxine, water, and glycerol-which was well tolerated and led to normalization of TSH levels.

CONCLUSION

Malabsorption of L-T4 is often seen in patients with Hashimoto's disease-related hypothyroidism and comorbid GI conditions, such as gastroparesis and SIBO. L-T4 tablets and a compounded oral suspension were inefficiently absorbed, leading to suboptimal TSH control. Switching to levothyroxine sodium oral solution resulted in sustained TSH control with subsequent resolution of symptoms. No side effects or reactions to the medication were observed, despite the patient's multiple allergies and sensitivities to food chemicals and medications.

A glimpse into the black box of celiac disease complications: a case report with a rare presentation

The purpose of this article is to report a case of celiac disease in a child with uncommon presentation and severe complications, and briefly review recent literature regarding celiac disease complications in children. We describe a case report of celiac disease in a child (to our knowledge, this is the first to be reported in its unique presentation in the Russian Federation) and precisely review its presenting complications with the exiting works of literature. Many cases of celiac disease in children who are not diagnosed and treated properly suffer from a plethora of complications due to malabsorption and concurrent autoimmune reactions that affect mainly but are not limited to the endocrine system. Complications of celiac disease in children should always be suspected, and evidence-based follow-up recommendations should be introduced as soon as possible because the burden of celiac disease complications in children is remarkable.

Over-the-counter protein supplement resulting in impaired thyroxine absorption in a hypothyroid patient

Summary

Whey protein is a popular dietary supplement that is claimed to provide multiple health benefits. It has been shown to delay gastric emptying and impair ileal nutrient absorption. Additionally, some of the other additives like papain enzyme, soy lecithin in these protein supplements could interfere with L-thyroxine absorption. There is no evidence in the literature for the effects of protein supplements on L-thyroxine absorption. Herein, we describe a case of a 34-year-old lady who was on endocrinology follow up for primary hypothyroidism with stable thyroid-stimulating hormone (TSH) levels within the normal range while on L-thyroxine with a dose of 125 µg daily for the last 3 years, presenting with mild hypothyroid symptoms and elevated TSH level following a recent introduction of a protein supplement by her physical care adviser. Her treatment adherence and ingestion technique were good throughout, she was not on other medications or herbal remedies, there were no other changes in her food pattern or features suggestive of malabsorption, she was not pregnant, was taking the same L-thyroxine brand and TSH test was done from the routine lab. Since the only factor which could have contributed to the deranged TSH levels was the recent introduction of the whey protein supplement, we advised her to stop the protein supplement while continuing the same dose of L-thyroxine. Her TSH level was repeated in 6 weeks and was found to be normal (1.7 mIU/L). Our case report demonstrates that over-the-counter protein supplements could interfere with L-thyroxine absorption. Therefore, patients on L-thyroxine should be cautious when taking them.

Learning points

Concomitant Use of Levothyroxine and Proton Pump Inhibitors in Patients with Primary Hypothyroidism: a Systematic Review

BACKGROUND

The aim of this study was to assess the effect of concomitant use of levothyroxine (LT4) and proton pump inhibitors (PPIs) on thyroid-stimulating hormone (TSH) levels in patients with primary hypothyroidism.

METHODS

A systematic review of interventional and observational studies that compared the TSH levels before and after concomitant use of LT4 and PPI was performed. Articles published in English up to September 1, 2019, were included. PubMed, EMBASE, and Cochrane Library databases. Gray literature was also searched in repositories, websites OpenGrey and Google Scholar, and abstracts of major international congresses. Study quality was assessed with the Newcastle-Ottawa quality assessment scale for observational studies and the Risk Of Bias In Non-randomized Studies - of Interventions (ROBINS-I) tool was used.

RESULTS

Five thousand twelve discrete articles were identified. Following assessment and application of eligibility criteria, seven studies were included. There was a considerable heterogeneity among the included studies in design, sample size, inclusion and exclusion criteria, treatment regimen, and baseline demographics. Each of the included studies showed an increase in TSH levels following LT4 and PPI consumption, and in the majority of these, the increase was statistically significant.

DISCUSSION

The concomitant use of LT4 and PPI showed a significant increase in TSH concentration. However, given the small number of studies, further research is needed to clarify the interfering role of PPI on LT4 intestinal absorption.

PROSPERO REGISTRATION NUMBER

CRD42020047084.

Levothyroxine sodium oral solution to control thyroid function in a patient with hypothyroidism and celiac disease

Implementing a gluten-free diet and switching to the levothyroxine oral solution significantly improved malabsorptive and hypothyroid symptoms in a patient with hypothyroidism, Addison's disease, and celiac disease without the need to increase levothyroxine dosage.

Preference, Adherence, and Maintenance of Euthyroidism Using 3 Different Regimens of Levothyroxine Intake during the Fasting Month of Ramadan

<b><i>Introduction:</i></b> Millions of Muslim hypothyroid patients fast during Ramadan. Limited data are available on the effect of fasting during Ramadan and different levothyroxine (L-T4) timings on thyroid status. The present study aimed to report preference, adherence, and maintenance of euthyroidism using 3 different regimens of L-T4 intake during Ramadan. <b><i>Methods:</i></b> This is a prospective study including Muslim hypothyroid patients fasting during Ramadan between 2018 and 2019. Patients freely chose between 3 regimens, regimen 1: to take L-T4 at sunset and postpone food and beverages for 60 min; regimen 2: to have iftar (first meal) at sunset, stop food and beverages for 3–4 h, have L-T4, and wait for 60 min before suhor (last meal); regimen 3: have suhor at midnight, stop food and beverages for 3–4 h, and have L-T4 before next fast. Thyroid status was assessed before and within 6 weeks after Ramadan. <b><i>Results:</i></b> 393 patients were included. The first 2 regimens or a combination of both was the most preferred by patients 40.5, 36.7, and 17%, respectively. 323/393 patients were adherent to L-T4 regimens (82.2%). 273/393 patients were euthyroid after Ramadan (69.5%). TSH pre- and post-Ramadan were 4.35 ± 12.30 mIU/L and 2.73 ± 3.37 mIU/L, respectively, with no statistically significant change (<i>p</i> = 0.225). Adherence was predicted post-Ramadan euthyroidism (odds ratio [OR] 2.8 in univariate and OR 2.96 in multivariate models). <b><i>Conclusions:</i></b> The first and second regimens or a combination of both was preferred by most patients. High rates of adherence and post-Ramadan euthyroidism were observed. Adherence to the preferred regimen is the main determinant of post-Ramadan euthyroidism.

New Formulations of Levothyroxine in the Treatment of Hypothyroidism: Trick or Treat?

Background: Levothyroxine (LT4) as a medication is used by up to 5.3% of the adult population. For optimal efficacy, the traditional tablet formulation (LT4tab) requires that patients avoid concomitant ingestion with food, drinks, and certain medications, as well as excellent patient compliance. Some comorbidities influence bioavailability of LT4 and may mandate repeated dose adjustments. Summary: New LT4 formulations (soft gel [LT4soft] and liquid [LT4liq]) containing predissolved LT4 are claimed to improve bioavailability, presumably by facilitating absorption. Thus, these formulations may well be more suitable than LT4tab for patients whose daily requirements are subjected to variations in bioavailability. Here, we review the evidence and indications for use of new LT4 formulations and highlight areas of uncertainty that are worthy of further investigation. While bioequivalence is established for LT4soft and LT4liq administered to healthy volunteers compared with LT4tab in pharmacokinetic (PK) studies, therapeutic equivalence of the new formulations seems to be different in several clinical settings. Some evidence suggests that new formulations of LT4 may mitigate against the strict requirements relating to concomitant ingestion with food, drinks, and certain medications, which apply to traditional LT4 tablets. The principal indication is in selected patients with disease fluctuations and intermittent therapies with interfering medications, where the need for frequent dose adjustments and office visits may be diminished. Whether the use of LT4soft or LT4liq in patients with impaired gastric acid secretion results in better control of hypothyroidism than LT4tab remains unclear. Conclusions: The evidence in favor of using LT4soft and LT4liq in clinical practice over LT4tab is weak, and the underlying putative PK mechanisms unclear. Additional studies to investigate these potential benefits, define the cost-effectiveness, and understand the PK mechanisms involved with new LT4 formulations are needed.

The Stability of TSH, and Thyroid Hormones, in Patients Treated With Tablet, or Liquid Levo-Thyroxine

Approximately, 5% of the population is affected by hypothyroidism, mainly women and persons aged more than 60 years. After the diagnosis of hypothyroidism the usual therapy is tablet levothyroxine (L-T4), with a monitoring of the thyroid-stimulating hormone (TSH) level in primary hypothyroidism every 6-8 weeks and L-T4 is adjusted as necessary to reach an euthyroid state. Once TSH is stabilized in the normal range, it is recommended to conduct annual testing in the treated subjects to warrant suitable replacement. More recently advances regarding L-T4 treatment are the introduction of new oral formulations: the liquid solution, and soft gel capsule. The soft gel capsule permits a quick dissolution in the acid gastric pH. The liquid preparation does not require an acid gastric environment. Many pharmacokinetic studies demonstrated a more rapid absorption for the liquid L-T4, or capsule, than with tablet. Many studies have shown that the liquid, or capsule, formulations can overcome the interaction with foods, drugs or malabsorptive conditions, that are able to impair the tablet L-T4 absorption. Lately studies have suggested that liquid L-T4 can permit to maintain more efficiently normal TSH levels in hypothyroid patients in the long-term follow-up, than tablet L-T4, both in patients with malabsorptive states, and in those without malabsorption. Further large, prospective, longitudinal studies are needed to evaluate the stability of TSH, in hypothyroid patients treated with different L-T4 formulations.

L-T4 Therapy in Enteric Malabsorptive Disorders

Levothyroxine (L-T4) absorption can be impaired by various causes: a) L-T4 ingestion during breakfast, or with food; b) conditions of reduced gastric acidity; c) intestinal procedures and diseases such as bariatric surgery, lactose intolerance (LI), celiac disease (CD), inflammatory bowel disease; d) drugs that alter L-T4 absorption, increasing the gastric pH, or preventing the dissolution of tablets. The development of new oral formulations, i.e. the liquid preparation and the soft gel capsule, represents the most recent advance regarding L-T4 therapy. Treating hypothyroidism with L-T4 tablets can lead to an improper control of thyroid-stimulating hormone (TSH) in ~10%-15% of patients. The improperly elevated TSH is usually managed by increasing the L-T4 daily dose, and revaluating TSH upon 2-6 months. The increase of the L-T4 dosage may cause iatrogenic hyperthyroidism, especially when the underlying disorders are cured. Liquid L-T4 can be administered in patients unable to swallow capsules or tablets, and this is one of its major benefits. Liquid L-T4 can: 1- overcome food and beverages interference; 2- bypass the malabsorption associated with an increased gastric pH; 3- circumvent the issue of malabsorption in patients who underwent bariatric surgery; 4-maintain TSH values under control better than L-T4 tablets in hypothyroid patients with typical or atypical CD, or in patients with LI. Few clinical studies evaluated soft gel L-T4 with encouraging findings in patients with gastric- or coffee-related malabsorption, or hypothyroid patients without malabsorption. Additional research is necessary to investigate liquid L-T4, or soft gel capsule, in other conditions of altered L-T4 absorption.

Managing symptoms in hypothyroid patients on adequate levothyroxine: a narrative review

The current standard of care for hypothyroidism is levothyroxine (LT4) monotherapy to reduce levels of thyrotropin (thyroid-stimulating hormone, TSH) within its reference range and amelioration of any symptoms. A substantial minority continues to report hypothyroid-like symptoms despite optimized TSH, however. These symptoms are not specific to thyroid dysfunction and are frequent among the euthyroid population, creating a therapeutic dilemma for the treating clinician as well as the patient. We present a concise, narrative review of the clinical research and evidence-based guidance on the management of this challenging population. The clinician may endeavor to ensure that the serum TSH is within the target range. However, the symptomatic patient may turn to alternative non-evidence-based therapies in the hope of obtaining relief. Accordingly, it is important for the clinician to check for conditions unrelated to the thyroid that could account for the ongoing symptoms such as other autoimmune conditions, anemia or mental health disorders. Systematic and thorough investigation of the potential causes of persistent symptoms while receiving LT4 therapy will resolve the problem for most patients. There may be some patients that may benefit from additional treatment with liothyronine (LT3), although it is unclear as yet as to which patient group may benefit the most from combined LT4 + LT3 therapy. In the future, personalized treatment with LT4 + LT3 may be of benefit for some patients with persistent symptoms of hypothyroidism such as those with polymorphisms in the deiodinase enzyme 2 (DIO2). For now, this remains a subject for research.

Alternative routes of levothyroxine administration for hypothyroidism

PURPOSE OF REVIEW

The aim of the article is to present the basics of oral levothyroxine (LT4) absorption, reasons why patients may have persistently elevated serum thyroid stimulation hormone (TSH) levels, and alternative strategies for LT4 dosing.

RECENT FINDINGS

Although oral LT4 tablets are most commonly used for thyroid hormone replacement in patients with hypothyroidism, case studies report that liquid oral LT4, intravenous, intramuscular, and rectal administration of LT4 can successfully treat refractory hypothyroidism.

SUMMARY

Hypothyroidism is one of the most common endocrine disorders encountered by primary care physicians and endocrinologists. LT4 is one of the most widely prescribed medications in the world and it is the standard of care treatment for hypothyroidism. Generally, hypothyroid patients will be treated with LT4 tablets to be taken orally, and monitoring will occur with routine serum thyroid tests, including TSH concentrations. However, many patients fail to maintain serum TSH levels in the target range while managed on oral LT4 tablets. A subset of these patients would be considered to have poorly controlled hypothyroidism, sometimes termed refractory hypothyroidism. For these patients, optimization of ingestion routines and alternative formulations and routes of administration of LT4 can be considered, including oral liquid, intravenous, intramuscular, and even rectal formulations.

REFRACTORY HYPOTHYROIDISM TO LEVOTHYROXINE TREATMENT: FIVE CASES OF PSEUDOMALABSORPTION

CONTEXT

A persistently elevated thyroid stimulating hormone (TSH) level is a common clinical problem in primary hypothyroidism patients treated with levothyroxine (LT4). "Pseudomalabsorption", which is characterized by poor adherence,should be considered in cases of refractory hypothyroidism after excluding other causes, such as malabsorption.

OBJECTIVE

We reviewed the features of the patients with persistently elevated TSH despite high-dose LT4 therapy.

DESIGN

Symptom evaluation, medications, comorbid diseases and physical examination features of five patients who applied to our outpatient clinic between 2016-2019 and diagnosed with LT4 pseudomalabsorption were retrospectively analyzed.

SUBJECTS AND METHODS

The LT4 loading test was performed with an oral dose of 1,000 µg LT4. Demographic parameters, BMI, thyroid function tests, laboratory parameters for malabsorption were recorded.

RESULTS

We observed at least two-fold increase of free thyroxine levels during the test, which was considered pseudomalabsorption. Euthyroidism was achieved in two patients by increasing the LT4 dosage and in one patient with a change in the preparation. TSH decreased significantly after being informed about compliance in one patient. Another one was given LT4 twice weekly, but TSH remained elevated because of nonadherence.

CONCLUSION

The LT4 loading/absorption test is a valuable tool to confirm the diagnosis of pseudomalabsorption. Informing patients, changing the preparation, increasing the dose, supervised intake of daily/weekly LT4 forms are treatment options for managing these cases.

Levothyroxine Treatment of Pregnant Women with Hypothyroidism: Retrospective Analysis of a US Claims Database

BACKGROUND

Approximately 2-4% of women of reproductive age have hypothyroidism. This study characterizes pregnant women with hypothyroidism and examines adherence to guidelines during pregnancy.

METHODS

Women age 18 to 49 who were pregnant in 2014 and identified with hypothyroidism (N = 3448) were included in the retrospective study. The analyses examined differences in characteristics and comorbidities between pregnant women treated with levothyroxine and untreated women and adherence to guidelines by measuring thyroid-stimulating hormone (TSH) target achievement for women treated with levothyroxine.

RESULTS

The average age was 32.76 years, and the median TSH value was 1.97 mIU/l. Compared with untreated pregnant women, pregnant women treated with levothyroxine were significantly younger, had a lower Charlson Comorbidity Index score and had lower rates of comorbid type 2 diabetes and migraines. Among women treated with levothyroxine, 52.61% had a last recorded TSH value consistent with American Thyroid Association (ATA) guidelines, 23.85% were undertreated, 1.03% were overtreated, and 22.52% did not have TSH monitored during their pregnancy.

CONCLUSIONS

A large percentage of pregnant women, including many treated with levothyroxine, was not treated in a manner consistent with clinical guidelines. Additionally, there were significant differences in general health and comorbidities between pregnant women treated with levothyroxine and those untreated.

Different Formulations of Levothyroxine for Treating Hypothyroidism: A Real-Life Study

OBJECTIVE

Hypothyroid patients are treated by sodium levothyroxine (LT4). Tablet is the mostly used LT4 formulation, and the fasting regimen is required for the absorption of active principle. Also, gastrointestinal diseases and drugs may impair the LT4 bioavailability when tablet is used. Nonsolid LT4 formulations (i.e., liquid solution (LS) and soft gel (SG) capsule) were manufactured to overcome the limitations of LT4 tablet. This study was conceived to evaluate the performance of nonsolid LT4 formulations in a real-life scenario.

METHODS

Two institutions participated in the study that was conducted in two phases (i.e., enrollment and re-evaluation). Adults with autoimmune or postsurgical hypothyroidism and on LT4 from a few months were selected. A nonparametric statistical analysis for paired or unpaired data was performed.

RESULTS

121 consecutive cases were included. At the enrollment phase, a 52% of patients took the therapy at least 30 min before breakfast with no difference between tablet and SG/LS users. TSH was 1.65 mIU/L (0.86-2.70) in patients on LT4 tablet and 1.70 mIU/L (1.10-2.17) in those on SG/LS (p=0.66). At the re-evaluation phase, among the patients using correct LT4 assumption, the TSH value was stable in the tablet group (p=0.66). At the re-evaluation phase, among the patients using correct LT4 assumption, the TSH value was stable in the tablet group (p=0.66). At the re-evaluation phase, among the patients using correct LT4 assumption, the TSH value was stable in the tablet group (p=0.66). At the re-evaluation phase, among the patients using correct LT4 assumption, the TSH value was stable in the tablet group (p=0.66). At the re-evaluation phase, among the patients using correct LT4 assumption, the TSH value was stable in the tablet group (.

CONCLUSION

The performance of nonsolid LT4 formulations is not influenced by correct or incorrect use of therapy. On the contrary, LT4 tablet does not guarantee euthyroidism when it is ingested without waiting for at least 30 minutes before breakfast. These new data, obtained in a real-life scenario, suggest that LT4 SG/LS should be regarded as first-line therapy for treating adults with newly diagnosed hypothyroidism.

Levothyroxine Therapy in Gastric Malabsorptive Disorders

Oral levothyroxine sodium is absorbed in the small intestine, mainly in the jejunum and the ileum being lower the absorption rate at duodenal level. The time interval between the ingestion of oral thyroxine and its appearance in the plasma renders unlike a gastric absorption of the hormone. However, several evidence confirm the key role of the stomach as a prerequisite for an efficient absorption of oral levothyroxine. In the stomach, in fact, occur key steps leading to the dissolution of thyroxine from the solid form, the process bringing the active ingredient from the pharmaceutical preparation to the aqueous solution. In particular, gastric juice pH, volume, viscosity, as well as gastric emptying time seem to be the most important limiting factors. These hypotheses are confirmed by the detection of an increased need for levothyroxine in patients with Helicobacter pylori infection, chronic atrophic gastritis, gastroparesis, or in simultaneous treatment with drugs interfering with gastric acidic output. The aim of the present article is to focus on the knowledge of pathophysiologic events that determine the absorptive fate of traditional (tablet) and alternative thyroxine preparations (softgel capsule and liquid solution) in patients bearing gastric disorders.

A case of H. pylori infection presenting as refractory hypothyroidism

We present the case of a 45-year-old lady with long standing hypothyroidism who was euthyroid on replacement for many years, but stopped responding even to supraphysiological doses of LT4 since the last five years. She complained of abdominal discomfort, bloating, and nausea. She did not have diarrhea or weight loss. Levothyroxine absorption test was done which was suggestive of malabsorption and she was started on triple therapy for H. pylori eradication after confirmation of diagnosis. After 10 days of treatment initiation, she developed symptoms of thyrotoxicosis with her supraphysiological dose of LT4, which was then tapered to a lower dose. Euthyroid state was ultimately achieved with lower doses of LT4 replacement.

Levothyroxine Absorption Test to Differentiate Pseudomalabsorption from True Malabsorption

BACKGROUND

The levothyroxine absorption test for evaluation of pseudomalabsorption in patients with primary hypothyroid is not standardised. An individual in whom a workup for malabsorption is warranted remains undefined.

METHODS

Twenty-five euthyroid, 25 newly diagnosed hypothyroid, 25 treated hypothyroid with normalised TSH, and 25 hypothyroid subjects with elevated TSH despite adequate dose of levothyroxine for more than 6 months, and 10 euthyroid subjects with true malabsorption were administered levothyroxine (10 μg/kg or maximum 600 μg) to study its absorption profile by measuring free T4 level at hourly intervals for 5 h. Results : Free T4 peaked at 3 h with marginal insignificant decline at 4 h in all groups. The increments of free T4 (between baseline and 3 h) of the four groups (except malabsorption) were not statistically different. The mean increment of free T4 in true malabsorption was 0.39 ng/dL (95% CI: 0.29-0.52) and it was 0.78 ng/dL (95% CI: 0.73-0.85) (10.4 pmol/L) for other groups combined together. The cut off of free T4 increment at 3 h from baseline above 0.40 ng/dL had a sensitivity of 97% and specificity of 80% (AUC 0.904, p < 0.001) to exclude true malabsorption.

CONCLUSION

Subjects with elevated TSH on adequate dose of LT4 can be reliably diagnosed to be non-adherent to treatment with levothyroxine absorption test. The incremental value above 0.40 ng/dL (5.14 pmol/L) at 3 h may be useful to identify individuals where workup of malabsorption is unwarranted.

Thyro-entero-gastric autoimmunity: Pathophysiology and implications for patient management

The association between autoimmune atrophic gastritis and thyroid disorders has been observed since the early 1960s and the expression "thyrogastric syndrome" was coined to indicate the presence of thyroid autoantibodies or autoimmune thyroid disease in patients with pernicious anemia, a late clinical stage of autoimmune atrophic gastritis. More recently, it was confirmed that autoimmune thyroid disorders, in particular Hashimoto's thyroiditis, may be frequently associated with other organ-specific, immune-mediated disorders, such as autoimmune atrophic gastritis or celiac disease. The association of Hashimoto's thyroiditis with autoimmune atrophic gastritis or celiac disease in adult patients is currently considered part of the polyglandular autoimmune syndromes which include several autoimmune disorders associated with an autoaggressive impairment of endocrine glands. From a clinical point of view, the thyro-entero-gastric autoimmunity may lead to potentially serious consequences like anemia, micronutrients deficiencies, and drugs malabsorption, as well as to an increased risk for malignancies. These alterations may frequently present in an underhand manner, with consequent diagnostic and treatment delays. Many aspects of the association between thyroid, gastric and intestinal autoimmune diseases still await clarification. The present review focuses on the embryological, genetic and pathophysiological aspects of thyro-entero-gastric autoimmunity. In particular, the current diagnostic criteria of autoimmune thyroid disease, autoimmune atrophic gastritis, and celiac disease are reviewed, along with the evidences for their association in poly-autoimmunity syndromes. The benefits of proactive screening of autoimmune thyroid disorders in patients with autoimmune gastritis or enteropathy and viceversa are also discussed.

Liquid and softgel capsules of l-thyroxine results lower serum thyrotropin levels more than tablet formulations in hypothyroid patients

Objective

Evidence indicates that L-T4 in liquid and softgel capsule are absorbed better than tablets in hypothyroid patients, even when patients are under medications that impair the intestinal absorption of L-T4. However, no study has evaluated all three L-T4 formulations in the same hypothyroid patients. This study aims to fill this gap. The outcome was the degree of TSH change in the liquid and softgel formulations, using tablet L-T4 as the reference, regardless of sequence of formulation and regardless of whether patients were co-ingesting with interfering medications.

Methods

We recorded serum TSH levels in two groups of L-T4 replaced patients with primary hypothyroidism (23 subjects who did not co-ingest interfering medications, and 20 subjects who did). Either group of patients took one formulation of L-T4 at a time with variable sequences. In the first group, the median durations of exposure to tablet, liquid or softgel L-T4 were 14, 9 and 10 months, respectively. In the second group the corresponding durations were 13, 11 and 10 months, during which patients co-ingested interfering medications.

Results

In the 23 patients, there were 78, 74 or 101 TSH determinations during liquid, softgel capsule or tablet L-T4 regimens. Serum TSH levels associated with liquid, capsule or tablet L-T4 were 1.62 ± 0.51, 1.77 ± 0.44 mU/L (P = 0.049 vs liquid) or 2.38 ± 0.69 mU/L (P < 0.0001 vs liquid or capsule). Rates of TSH ≤ 2.50 mU/L were 97.4% (liquid), 95.9% (softgel) or 64.4% (tablet, P < 0.0001 vs liquid or capsule). Rates of TSH ≤ 4.12 mU/L were 100%, 100% or 98.0%.

In the 20 patients, the corresponding TSH determinations were 56, 57 and 41, and corresponding TSH levels were 2.74 ± 0.98, 2.70 ± 0.79 or 7.53 ± 2.82 mU/L. Rates of TSH ≤ 2.50 mU/L were 51.8% (liquid), 47.4% (capsule, P = 0.64) or 2.4% (tablet, P < 0.0001 vs liquid or capsule). Rates of TSH ≤ 4.12 mU/L were 92.8% (liquid), 94.7% (capsule, P = 0.68) or 12.2% (tablet, P < 0.0001 vs liquid or capsule).

Conclusions

L-T4 ingested as liquid solution or softgel capsule is more bioavailable compared to L-T4 ingested as tablet, and it is slightly superior to capsule L-T4 only in the absence of co-ingestion of interfering medications.

Treatment with Intramuscular Levothyroxine in Refractory Hypothyroidism

INTRODUCTION

Orally and daily levothyroxine (LT4) is the treatment of choice for hypothyroidism. In the majority of cases, the lack of effectiveness by this way may be due to poor adherence; however, gastrointestinal malabsorption may explain more cases of thyroxine refractoriness than previously reputed, due to the number of occult forms of these disorders.

CASE PRESENTATION

A 55-year-old white man with a diagnosis of low risk of recurrence of follicular variant of papillary thyroid carcinoma was treated with total thyroidectomy, 30 mCi iodine 131, and oral LT4. A year before he presented a gastric adenocarcinoma that required a partial gastrectomy. He evolved with multiple episodes of intestinal subocclusion that had to be treated with enterectomy in the first instance, then digestive rest and total parenteral nutrition. In spite of having made increases in oral LT4 dose (3 µg/kg), the patient persisted with a thyroid-stimulating hormone level >100 mIU/L. For this reason, we decided to administer intramuscular LT4.

CONCLUSION

Since there are no guidelines or consensus of intramuscular LT4 use, our experience and how we decided the dose and way of administration are presented in this article to contribute to future cases.

The Levothyroxine Absorption Test: A Four-Year Experience (2015-2018) at The Mayo Clinic

Background: Levothyroxine (LT4) is the mainstay of therapy for hypothyroidism. Yet, despite physician efforts at dose titration, some patients remain hypothyroid on LT4 doses in excess of weight-based calculations, a condition known as refractory hypothyroidism. The LT4 absorption test (LT4AT) has been proposed to have utility in these patients by enabling distinction of LT4 malabsorption from pseudomalabsorption, a condition of intentional nonadherence. Given its rare use in clinical practice, we reviewed our institution's experience with the LT4AT to assess its impact on management of refractory hypothyroidism. Methods: We reviewed the charts of 16 patients diagnosed with refractory hypothyroidism and who had completed the LT4AT between January 2015 to January 2019. The primary aim was to determine the utility of this test in distinguishing LT4 malabsorption from pseudomalabsorption. Secondary aims were to determine whether the results of this test impacted physicians' management decisions, as well as to report on clinical outcomes at follow-up. Our LT4AT is a six-hour test wherein patients receive a weight-based dose of LT4 followed by serial measurements of total thyroxine (TT4) and thyrotropin (TSH). Percentage absorption is calculated using the following formula, with normal absorption being ≥60%: [Formula: see text] Results: Percentage absorption was calculated in 13 of 16 patients due to lack of TT4 data for 3 patients. Absorption was impaired in one patient (% absorbed = 0), who had known causes of malabsorption. The remaining 12 patients had normal absorption by hour 4 of the test (% absorption 60-158) in conjunction with upward TT4 trends. Clinical follow-up ranged from 1 to 32 months (median 6.5 months), with 11 patients having follow-up data. Six of these had normal or suppressed TSH values at most recent follow-up, and four had improved but persistent TSH elevations. The one said patient with malabsorption improved with intravenous LT4. Conclusions: The LT4AT can provide valuable information for distinguishing malabsorption from pseudomalabsorption. Our findings support the combined use of calculated percentage absorptions with TT4 trends for at least a four-hour time frame when making determinations regarding absorption.

Novel thyroxine formulations: a further step toward precision medicine

Levothyroxine (T4) is a critical-dose drug, because little variations in the blood concentration may cause treatment failure as well as iatrogenic thyrotoxicosis. Despite the dose response of this drug being more carefully titrated nowadays, several papers still report that a significant fraction of patients treated with levothyroxine demonstrate a TSH which is not on target. Moreover, some widespread gastrointestinal disorders as well as interfering drugs and foods may cause the "refractoriness" of a significant number of patients to an expected dose of thyroxine. The increasing awareness of the mechanisms interfering with the oral thyroid hormone bioavailability and the body of evidence regarding the complexity of treatment in certain classes of patients prompted pharmaceutical research to identify new hormonal formulations to optimize the performance of this drug. In this brief review, the progression of the scientific knowledge of novel T4 formulations use has been analyzed.