Pharmacokinetics and Comparative Bioavailability of a Levothyroxine Sodium Oral Solution and Soft Capsule

Preparation of altrenogest soft capsules and their bioequivalence in gilts

Introduction

Altrenogest (ALT) is widely used to regulate the estrous cycle of sows and mares; however, currently used oral solutions of ALT are deficient in terms of dose accuracy and stability during use. To resolve these problems, we aimed to prepare softgel capsules of ALT with a unit dose equal to the clinically administered dose.

Method

The shell of the softgel capsule was mainly composed of gelatin and glycerol, with titanium dioxide and red iron oxide as masking agents. Using the shake flask method, the contents were screened for ethyl acetate as a lipophilic solubilizing carrier based on soya bean oil. The contents were automatically filled and compressed into softgel capsules by a softgel capsule machine. The quality of the prepared softgel capsules was evaluated through a drug content test, an in vitro release test, and stability studies. Furthermore, bioequivalence studies were conducted with atrenogest oral solution.

Results

The content is an ALT concentration of 2% oil solution and the specification of the softgel is 20 mg/capsule. In in vitro dissolution experiments, the softgel capsules were rapidly disintegrated and released in three different pH buffers, with a cumulative release rate of nearly 100% at 1 h. The softgel capsules were stable at high temperature and under strong light for 10 days, and the concentration of ALT was >99% in the 6-month accelerated and long-term tests. In the bioequivalence study, Tmax of the softgel capsules was 2.20 ± 0.77 h, t 1/2 was 6.36 ± 1.74 h, and C max was 64.65 ± 20.69 ng/ml. The main pharmacokinetic parameters T max, C max, AUC 0-t, and AUC 0-∞, did not differ significantly between the softgel capsules and the commercially available ALT oral solution (P > 0.05), and bioequivalence was demonstrated within the 90% confidence interval.

Conclusion

The prepared softgel capsules have the advantages of higher content, ease of use with accurate dosing, good stability, and equivalence to ALT oral solution, implying that our softgels are ready for clinical use.

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.

Development and In Vivo Evaluation of Sustained Release Microparticles Loaded with Levothyroxine for Hypothyroidism Treatment

Hypothyroidism is a chronic condition combated by a daily oral supplementation of levothyroxine. In addition to the need for frequent dosing, oral administration may result in variable absorption of the drug leading to a failure in achieving normal thyroid function. Therefore, the development of a long-acting injectable system capable of delivering the drug is necessary. This work was aimed at developing sustained release microparticles loaded with levothyroxine. The microparticles were produced through the emulsification-solvent evaporation method using 2 grades of biocompatible and biodegradable polyesters: poly(ᴅ,ʟ-lactide-co-glycolide) (PLGA) and poly(ᴅ,ʟ-lactide) (PLA). Both polymers produced microparticles with very similar sizes (1.9 µm) and zeta potential values (around -22.0 mV). However, PLA microparticles had a significantly higher drug loading (6.1% vs. 4.4%, respectively) and encapsulation efficiency (36.8%, vs. 26.1%, respectively) when compared to PLGA counterparts. While both types of microparticles displayed a biphasic release pattern in vitro, a slower rate of release was observed with PLA microparticles. Moreover, a similar biphasic release pattern was found in vivo, with an initial phase of rapid release followed by a slower phase in the subsequent 10 days. These results indicate the possibility of developing levothyroxine loaded polyester microparticles as a potential long-acting thyroid hormone replacement therapy.

The Bioavailability of Drugs-The Current State of Knowledge

Drug bioavailability is a crucial aspect of pharmacology, affecting the effectiveness of drug therapy. Understanding how drugs are absorbed, distributed, metabolized, and eliminated in patients' bodies is essential to ensure proper and safe treatment. This publication aims to highlight the relevance of drug bioavailability research and its importance in therapy. In addition to biochemical activity, bioavailability also plays a critical role in achieving the desired therapeutic effects. This may seem obvious, but it is worth noting that a drug can only produce the expected effect if the proper level of concentration can be achieved at the desired point in a patient's body. Given the differences between patients, drug dosages, and administration forms, understanding and controlling bioavailability has become a priority in pharmacology. This publication discusses the basic concepts of bioavailability and the factors affecting it. We also looked at various methods of assessing bioavailability, both in the laboratory and in the clinic. Notably, the introduction of new technologies and tools in this field is vital to achieve advances in drug bioavailability research. This publication also discusses cases of drugs with poorly described bioavailability, providing a deeper understanding of the complex challenges they pose to medical researchers and practitioners. Simultaneously, the article focuses on the perspectives and trends that may shape the future of research regarding bioavailability, which is crucial to the development of modern pharmacology and drug therapy. In this context, the publication offers an essential, meaningful contribution toward understanding and highlighting bioavailability's role in reliable patient treatment. The text also identifies areas that require further research and exploration.

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.

Ionic Levothyroxine Formulations: Synthesis, Bioavailability, and Cytotoxicity Studies

Thyroid diseases affect a considerable portion of the population, with hypothyroidism being one of the most commonly reported thyroid diseases. Levothyroxine (T4) is clinically used to treat hypothyroidism and suppress thyroid stimulating hormone secretion in other thyroid diseases. In this work, an attempt to improve T4 solubility is made through the synthesis of ionic liquids (ILs) based on this drug. In this context, [Na][T4] was combined with choline [Ch]+ and 1-(2-hydroxyethyl)-3-methylimidazolium [C2OHMiM] + cations in order to prepare the desired T4-ILs. All compounds were characterized by NMR, ATR-FTIR, elemental analysis, and DSC, aiming to check their chemical structure, purities, and thermal properties. The serum, water, and PBS solubilities of the T4-ILs were compared to [Na][T4], as well as the permeability assays. It is important to note an improved adsorption capacity, in which no significant cytotoxicity was observed against L929 cells. [C2OHMiM][T4] seems to be a good alternative to the commercial levothyroxine sodium salt with promising bioavailability.

Levothyroxine: Conventional and novel drug delivery formulations

Despite the fact that levothyroxine is one of the most prescribed medications in the world, its bioavailability has been reported to be impaired by many factors, including interfering drugs or foods and concomitant diseases, and persistent hypothyroidism with a high dose of levothyroxine is thus elicited. Persistent hypothyroidism can also be induced by noninterchangeability between formulations and poor compliance. To address these issues, some strategies have been developed. Novel formulations (liquid solutions and soft-gel capsules) have been designed to eliminate malabsorption. Some other delivery routes (injections, suppositories, sprays, and sublingual and transdermal administrations) are aimed at circumventing different difficulties in dosing, such as thyroid emergencies and dysphagia. Moreover, nanomaterials have been used to develop delivery systems for the sustained release of levothyroxine to improve patient compliance and reduce costs. Some delivery systems encapsulating nanoparticles show promising release profiles. In this review, we first summarize the medical conditions that interfere with the bioavailability of oral levothyroxine and discuss the underlying mechanisms and treatments. The efficacy of liquid solutions and soft-gel capsules are systematically evaluated. We further summarize the novel delivery routes for levothyroxine and their possible applications. Nanomaterials in the levothyroxine field are then discussed and compared based on their load and release profile. We hope the article provides novel insights into the drug delivery of levothyroxine.

A Novel Levothyroxine Solution Results in Similar Bioavailability Whether Taken 30 or Just 15 Minutes Before a High-Fat High-Calorie Meal

Background: Levothyroxine (LT4) sodium is a standard treatment for hypothyroidism. Its absorption and bioavailability when taken as a tablet have been shown to be significantly decreased with concomitant food ingestion. Therefore, LT4 formulations are recommended to be taken on an empty stomach, at least 30, ideally 60, minutes before breakfast, potentially affecting adherence to therapy. A novel LT4 solution (Tirosint^®-SOL) has been shown to result in a faster absorption process than tablets or soft-gel capsule formulations. The objective of this trial was to evaluate the bioavailability of this preparation taken 15 minutes before a high-fat high-calorie meal in comparison with the minimally recommended 30-minute interval. Methods: Thirty-six (33 completers, 24 males and 9 females) healthy volunteers participating in the randomized study took 600 mcg of LT4 oral solution, single doses after a 10-hour fast, 15 or 30 minutes before a high-fat, high-calorie, FDA-approved standardized meal in a controlled research setting. We measured serum total thyroxine using Liquid Chromatography with Tandem Mass Spectrometry at baseline and multiple time points up to 72 hours after LT4 administration. The predefined equivalence boundaries for the extent of exposure reflected by the area under the curve (AUC) were 80-125%. The washout period was at least 35 days. Results: The geometric mean ratios and confidence intervals (CIs) for the baseline-adjusted extent of exposure represented by AUCs truncated at both 48 and 72 hours after dosing (AUC_0-48: 90% [90% CI 86-94]; and AUC_0-72: 92% [90% CI 87-97]) were within the prespecified equivalence boundaries. The baseline-adjusted peak concentration was also clinically similar (C_max: 85% [90% CI 80-90]). The median t_max was 1.5 hours in each group. The rate of adverse events was similar between groups. Conclusions: We observed no significant difference in the pharmacokinetic properties of a novel LT4 solution administered 15 and 30 minutes before a high-fat high-calorie meal in normal subjects. Further research is needed to evaluate (a) the differences in overall bioavailability at other time points (including immediately premeal) and (b) the real-world effectiveness of this preparation in newly proposed administration conditions to optimize treatment outcomes in hypothyroid patients.

Pharmacokinetics and Clinical Implications of Two Non-Tablet Oral Formulations of L-Thyroxine in Patients with Hypothyroidism

BACKGROUND

Increased knowledge of the pharmacokinetic characteristics of orally administered levothyroxine (L-T₄) has improved individualization of dosing regimens. However, up to 40-45% of patients, depending on the leading cause of hypothyroidism, are still over- or, more often, undertreated. Unintentional non-adherence to L-T₄ replacement therapy includes all situations of unintended drug-drug and drug-food interactions as well as fasting conditions that are not necessarily respected by patients.

RESULTS

In this specific context, the overall information concerning those factors with the potential to affect L-T₄ absorption refers only to tablet formulation. Indeed, this is the reason why new non-tablet formulations of L-T₄ were introduced some years ago. In this regard, the current literature review was designed to summarize pharmacokinetic, drug and food interactions and clinical data focusing on two new oral L-T₄ formulations, i.e., liquid and soft-gel capsule in healthy volunteers and patients with primary hypothyroidism. The non-tablet L-T₄ soft-gel capsules and solution have proven bioequivalence with the usual L-T₄ tablet Princeps and generic formulations. Clinical studies have suggested higher performance of non-tablet formulations than tablet in those patients with suboptimal adherence. The impact of gastrointestinal conditions and variation of gastric pH was lower with either soft gel/solution than with tablets. In addition, the extent of drug-drug and drug-food interactions remains low and of uncertain clinical relevance.

CONCLUSIONS

Pending further studies allowing one to extend the use of soft-gel/solution preparations in unselected patients, non-tablet L-T₄ formulations should be considered as a first-line choice, especially in those patients with moderate-to-high potential of suboptimal tablet performance.

New-Onset Heart Failure in the Setting of T4-Conversion Disorder

Thyroid hormone is essential in accomplishing the appropriate metabolism of the body. Achieving euthyroidism is of importance due to the deadly ramifications of being hypothyroid, such as multiple organ failure, profound decrease in mentation and even death.

We present a case of an 80-year-old female with a history of hypertension, coronary artery disease, chronic kidney disease, hypothyroidism due to total thyroidectomy, and a cerebral vascular accident who presented with slurred speech, decreased appetite, dizziness and lethargy with new-onset weakness. She was adherent to all her medications. Her labs were significant for elevated thyroid-stimulating hormone, elevated free thyroxine, and low total triiodothyronine. Brain MRI revealed no acute pathology. She was given her home dose of Levothyroxine and was admitted to the telemetry unit for evaluation of her symptoms and abnormal thyroid panel. During her hospital course, she was found to have an abnormal rhythm and worsening lethargy. Subsequent electrocardiogram and laboratory values revealed new T-wave inversions and elevated troponin. An echocardiogram revealed a new severely reduced left ventricular function with severe global hypokinesis of the left ventricle and an ejection fraction of 30%. It was only after initiating combination therapy of levothyroxine and liothyronine that her symptoms and abnormal cardiac rhythm resolved. With this careful titration of the patient’s medication, we concluded that combination therapy was essential to the patient being euthyroid. This phenomenon was also cited in multiple literature, which warrants an investigation of a certain population’s inability to convert T4 to T3.

By sharing this case, we aim to aid providers with their differential diagnoses and bring to light a potential area of further investigation. Ultimately, by optimizing and tailoring these medications, we hope to improve their quality of life. 

Tea consumption affects the absorption of levothyroxine

Levothyroxine (LT4) is a convenient treatment for hypothyroidism. Coffee, however, prevents the body from efficaciously absorbing LT4. It is unknown whether the intake of tea interferes with LT4 absorption. Thirty-seven hypothyroidism patients with the following types of consumption were recruited: 1) only tea, 2) tea and coffee, and 3) only coffee. The concentrations of thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) were recorded before and 3 months after changing the consumption. The patients had reductions in the concentration of TSH to varying degrees after 3 months (p < 0.001 or p < 0.05). The natural logarithms of the differences between the concentrations of TSH before and after the change in the consumption (Δln-TSH) of tea and coffee, only coffee, and only tea were 1.94, 2.00, and 2.18, respectively. Long-term consumption of tea, like coffee, interfered with the absorption of LT4. We believe that avoiding tea when taking LT4 will reduce malabsorption.

Development and validation of a high-performance liquid chromatography method for levothyroxine sodium quantification in plasma for pre-clinical evaluation of long-acting drug delivery systems

Levothyroxine (LEVO) sodium is an FDA-approved drug that is used to treat underactive thyroid (hypothyroidism) and other conditions. It is generally used as a thyroid-stimulating hormone administered orally. However, this approach has some drawbacks such as this drug should be taken every day 30 min to 1 h prior to breakfast with an empty stomach, moreover, some food interactions must be monitored. Thus, alternative innovative approaches capable of providing sustained LEVO release should be developed. Our research was designed to establish a simple quantitative determination method for LEVO in rat plasma for pre-clinical evaluation of long acting formulations using a high-performance liquid chromatography method, to validate the analytical method according to ICH guidelines and to characterise its pharmacokinetic behavior in rats. After simple protein precipitation with acetonitrile, LEVO was eluted on a Xselect CSH™ C18 column (Waters, 3.0 × 150 mm) with a particle size of 3.5 μm using a mobile phase of water and acetonitrile at a ratio of 65 : 35% v/v, including 0.1% v/v of trifluoracetic acid. The calibration standards used for plasma ranged between 0.5-1000 ng mL^-1 with a correlation coefficient (r²) of ≥0.998. The limit of detection was 0.44 ng mL^-1 and the lower limit of quantitation was 1.33 ng mL^-1. The extraction recovery of LEVO in rat plasma samples by this method was between 80 and 85%. The method was selective, sensitive, accurate and precise for detecting and quantifying LEVO in a pharmacokinetic study carried out in rats for pre-clinical evaluation of long acting formulations. The validated HPLC method meets the ICH established requirements and therefore offers a wide range of potential applications in pre-clinical therapeutic drug monitoring, pharmacokinetics and toxicology.

Levothyroxine sodium pentahydrate tablets - formulation considerations

Even though levothyroxine sodium pentahydrate tablets have been in the market since 1955, there continue to be recalls due to sub potency. We have comprehensively reviewed the factors affecting its stability in solid oral dosage forms. A compilation of marketed formulation compositions enabled the identification of the potential 'problem excipients'. Two excipient properties, hygroscopicity and microenvironmental acidity, appeared to be responsible for inducing drug instability. In drug products, depending on the formulation composition and storage conditions, the pentahydrate can dehydrate to highly reactive levothyroxine sodium monohydrate, or undergo salt disproportionation to the free acid form of the drug. The USP assay method (HPLC based) is insensitive to these different physical forms of the drug. The influence of physical form of levothyroxine on its chemical stability is incompletely understood. The USP has five product-specific dissolution tests reflecting the complexity in its evaluation.

Comparative efficacy of early morning versus bedtime administration of levothyroxine in children with hypothyroidism: a prospective, open label, randomized, case-control study

INTRODUCTION

Studies in adults with hypothyroidism suggest an equal efficacy of bedtime versus early morning intake of levothyroxine. There is limited data on timing of levothyroxine administration in children.

MATERIAL AND METHODS

Children with hypothyroidism on early morning levothyroxine, and clinically and biochemically euthyroid, were assigned to receive levothyroxine at bedtime (group A) or were continued on early morning levothyroxine intake (group B). Clinical, anthropometric and laboratory evaluation (thyroid and lipid profiles, liver enzymes and creatinine) was done at baseline, and at 3 and 6 months.

RESULTS

Eighty-four children, 42 in each group, completed the study. The clinical and anthropometric parameters remained similar in the two groups at baseline and at 3- and 6-month follow-up visits. There was no difference in the mean serum concentrations of triiodothyronine, thyroxine and thyrotropin at the 3 time-points in the study. In addition, mean serum aspartate transaminase, alanine transaminase, creatinine and parameters of lipid profiles remained similar in the two groups. The requirement of levothyroxine was similar at baseline (48.6 ±16.9 µg vs. 49.6 ±19.5 µg, p-value 0.80) and at the endpoint (48.3 ±17.2 µg vs. 51.9 ±18.0 µg, p-value 0.46) in both groups. At the study end, 25 (60%) patients in group A and 17 (40%) in group B preferred bedtime dosing of levothyroxine.

CONCLUSIONS

We found an equal efficacy of bedtime intake compared to early morning intake of levothyroxine in maintaining an euthyroid state in children with hypothyroidism. Further studies are required to see if bedtime levothyroxine administration improves the quality of life of patients.

Mortality Risk Profiling of Staphylococcus aureus Bacteremia by Multi-omic Serum Analysis Reveals Early Predictive and Pathogenic Signatures

Staphylococcus aureus bacteremia (SaB) causes significant disease in humans, carrying mortality rates of ∼25%. The ability to rapidly predict SaB patient responses and guide personalized treatment regimens could reduce mortality. Here, we present a resource of SaB prognostic biomarkers. Integrating proteomic and metabolomic techniques enabled the identification of >10,000 features from >200 serum samples collected upon clinical presentation. We interrogated the complexity of serum using multiple computational strategies, which provided a comprehensive view of the early host response to infection. Our biomarkers exceed the predictive capabilities of those previously reported, particularly when used in combination. Last, we validated the biological contribution of mortality-associated pathways using a murine model of SaB. Our findings represent a starting point for the development of a prognostic test for identifying high-risk patients at a time early enough to trigger intensive monitoring and interventions.

Optimization and in Vitro Evaluation of Injectable Sustained-Release of Levothyroxine Using PLGA-PEG-PLGA

Purpose

In situ-forming gels (semi-solid state) (ISFGs) are widely used as sustained drug delivery, but they show a high burst release as well. The purpose of the current study is to make triblock that can make a quick gel on injection with a minimum burst release.

Methods

In this study, to control the release of levothyroxine from ISFG, PLGA-PEG-PLGA (triblock) polymer was used. The melting method was employed to synthesize the triblock via ring-opening polymerization (ROP). Different weight percentages of triblock in the formulation were investigated to reach the minimum initial burst release of levothyroxine from ISFGs. Furthermore, the results of the in-situ forming implant (solid-state) (ISFI) of levothyroxine prepared from PLGA 504 H polymers were compared with ISFG.

Results

The melting method employed in this study showed a successful ROP of the triblock. As the % triblock concentration was increased from 30 to 50%, the initial burst release decreased significantly. The initial burst release levothyroxine from ISFG (6.52 ± 0.30%) was much lower than the amount of levothyroxine released from ISFI (14.15 ± 0.79%). No cytotoxicity was observed for the sustained-release formulation containing ISFG 50% according to the MTT assay.

Conclusion

The results indicated that this formulation was safe to be administered subcutaneously. As the synthesized triblock has thermosensitive properties, and also has the hydrogen bonding between the N-methyl pyrrolidone molecules and PEG, therefore, these properties make ISFG formulation to have a smaller initial burst release compared to ISFI formulation.

Levothyroxine Formulations: Pharmacological and Clinical Implications of Generic Substitution

Oral levothyroxine (LT4) is the standard therapy for patients with hypothyroidism. Oral LT4 is available in several formulations, including tablets, soft gel capsules and oral solution. Multiple brand-name and generic LT4 tablets are available. In the US, the Food and Drug Administration (FDA) has developed a protocol for establishing bioequivalence of LT4 formulations based on serum thyroxine (T4) levels after a single oral dose administered to healthy volunteers. This protocol has been criticized by professional endocrinology associations for using healthy individuals and ignoring serum thyroid-stimulating hormone (TSH) levels. In addition, the protocol did not initially correct for baseline T4 levels, although this was changed in a later version. There are concerns that the FDA's protocol could allow products with clinically significant differences in bioavailability to be declared therapeutically equivalent and interchangeable. Once a generic LT4 has been shown to be bioequivalent to a brand-name LT4, it may be substituted for that brand-name LT4 with no need for dose adjustment or follow-up therapeutic monitoring. Often, the substitution is made by the pharmacy without the physician's knowledge. Even small differences between LT4 formulations can cause significant changes in TSH levels. This may be a particular concern in vulnerable populations, including elderly, pregnant, and pediatric patients. Problems that can be encountered when switching between formulations or when original products are reformulated are discussed in this review. These problems include altered efficacy and adverse events, some of which can be caused by excipients. Patients should be maintained on the same LT4 preparation if possible. If the LT4 preparation is changed, TSH levels should be evaluated and, if necessary, the dose of LT4 adjusted.Funding: Merck.Plain Language Summary: Plain language summary available for this article.

Diagnosis and management of hypopituitarism

PURPOSE OF REVIEW

This review summarizes pituitary function, and the clinical presentation and treatment of hypopituitarism.

RECENT FINDINGS

Updates in the field include new guidelines and meta-analyses on the diagnosis and treatment of select hormone deficiencies, novel treatment options, and advances in next generation sequencing technology.

SUMMARY

Hypopituitarism is defined as partial or complete loss of a single or multiple pituitary hormones. The clinical presentation of hypopituitarism varies depending on the number and severity of hormone deficiencies. Treatment involves the physiologic replacement of the individual end-organ hormone deficiencies and requires close lifelong monitoring.