Safety and Efficacy of Tolvaptan in Korean Patients with Hyponatremia Caused by the Syndrome of Inappropriate Antidiuretic Hormone

Duloxetine-Induced Antidiuresis in Rats with Lithium-Induced Nephrogenic Diabetes Insipidus

Antidepressants, including duloxetine, are a significant cause of drug-induced hyponatremia, which can disrupt the continuation of medication. Tolvaptan is beneficial for correcting hyponatremia caused by the syndrome of inappropriate antidiuresis, but its impact on duloxetine-induced hyponatremia remains unknown. We used male Sprague-Dawley rats to examine the impact of duloxetine treatment on lithium-induced nephrogenic diabetes insipidus (Li-NDI) and to evaluate whether the results were reversed by co-treatment with tolvaptan. To induce Li-NDI, lithium chloride (40 mmol lithium/kg dry food) was administered for 2 weeks. Duloxetine (50 mg/kg/day) and tolvaptan (10 mg/kg/day) were also administered in food to assess their individual effects over the same period. At the end of each animal experiment, kidneys were harvested to measure levels of cAMP, vasopressin-2 receptor (V2R), cAMP-responsive element binding protein 1 (CREB-1), aquaporin-2 (AQP2), and prostaglandin E2 (PGE2). Water diuresis was induced in the Li-NDI rats, and duloxetine treatment reduced polyuria while increasing urine osmolality. Duloxetine treatment prevented the decrease in total AQP2, AQP2 phosphorylation at serine 256, and CREB-1 phosphorylation in Li-NDI rats. The V2R mRNA level was also reduced in Li-NDI rats and restored by duloxetine treatment. In the subsequent experiment, the decreased water diuresis in Li-NDI rats treated with duloxetine was reversed by co-treatment with tolvaptan. Tolvaptan co-treatment also reversed the changes in AQP2 protein and CREB-1 phosphorylation in the renal cortex and medulla. The decreased cAMP levels in Li-NDI rat kidneys were elevated by duloxetine treatment, and this elevation was reversed by co-treatment with tolvaptan. However, the elevated PGE2 levels in Li-NDI rat kidneys were not affected by either duloxetine alone or tolvaptan co-treatment. In conclusion, antidiuresis was induced by duloxetine in Li-NDI and reversed by tolvaptan co-treatment through alterations in the V2R-cAMP-AQP2 pathway. These findings could underlie the mechanism of duloxetine-induced hyponatremia and suggest the potential usefulness of tolvaptan in treating drug-induced hyponatremia.

Syndrome of Inappropriate Antidiuresis: From Pathophysiology to Management

Hyponatremia is the most common electrolyte disorder, affecting more than 15% of patients in the hospital. Syndrome of inappropriate antidiuresis (SIAD) is the most frequent cause of hypotonic hyponatremia, mediated by nonosmotic release of arginine vasopressin (AVP, previously known as antidiuretic hormone), which acts on the renal V2 receptors to promote water retention. There are a variety of underlying causes of SIAD, including malignancy, pulmonary pathology, and central nervous system pathology. In clinical practice, the etiology of hyponatremia is frequently multifactorial and the management approach may need to evolve during treatment of a single episode. It is therefore important to regularly reassess clinical status and biochemistry, while remaining alert to potential underlying etiological factors that may become more apparent during the course of treatment. In the absence of severe symptoms requiring urgent intervention, fluid restriction (FR) is widely endorsed as the first-line treatment for SIAD in current guidelines, but there is considerable controversy regarding second-line therapy in instances where FR is unsuccessful, which occurs in around half of cases. We review the epidemiology, pathophysiology, and differential diagnosis of SIAD, and summarize recent evidence for therapeutic options beyond FR, with a focus on tolvaptan, urea, and sodium-glucose cotransporter 2 inhibitors.

Tolvaptan for the treatment of the syndrome of inappropriate antidiuresis (SIAD)

The syndrome of inappropriate antidiuresis (SIAD), the commonest cause of hyponatraemia, is associated with significant morbidity and mortality. Tolvaptan, an oral vasopressin V2-receptor antagonist, leads through aquaresis to an increase in serum sodium concentration and is the only medication licenced in Europe for the treatment of euvolaemic hyponatraemia. Randomised controlled trials have shown that tolvaptan is highly efficacious in correcting SIAD-related hyponatraemia. Real-world data have confirmed the marked efficacy of tolvaptan, but they have also reported a high risk of overly rapid sodium increase in patients with a very low baseline serum sodium. The lower the baseline serum sodium, the higher the tolvaptan-induced correction rate occurs. Therefore, a lower starting tolvaptan dose of 7.5 mg has been evaluated in small cohort studies, demonstrating its efficacy, but it still remains unclear as to whether it can reduce the risk of overcorrection. Most international guidelines, except for the European ones, recommend tolvaptan as second-line treatment for SIAD after fluid restriction. However, the risk of unduly rapid sodium correction in combination with its high cost have limited its routine use. Prospective controlled studies are warranted to evaluate whether tolvaptan-related sodium increase can improve patient-related clinical outcomes, such as mortality and length of hospital stay in the acute setting or neurocognitive symptoms and quality of life in the chronic setting. In addition, the potential role of a low tolvaptan starting dose needs to be further explored. Until then, tolvaptan should mainly be used as second-line treatment for SIAD, especially when there is a clinical need for prompt restoration of normonatraemia. Tolvaptan should be used with specialist input according to a structured clinical pathway, including rigorous monitoring of electrolyte and fluid balance and, if needed, implementation of appropriate measures to prevent, or when necessary reverse, overly rapid hyponatraemia correction.

Using Tolvaptan to Treat Hyponatremia: Results from a Post-authorization Pharmacovigilance Study

Introduction

Hyponatremia is a common condition of varying etiology among hospitalized patients and is associated with adverse outcomes. Treatment to normalize serum sodium is advisable. Tolvaptan received European Union marketing authorization for hyponatremia secondary to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Post-marketing pharmacovigilance activities were required to characterize the safety profile of tolvaptan more fully in this population, which is often elderly with a high burden of comorbid illness.

Methods

This was a prospective, observational, multinational, post-authorization pharmacovigilance study (NCT01228682) in seven European countries. Hospitalized patients were enrolled who received tolvaptan for hyponatremia associated with SIADH and consented to data collection. Tolvaptan was initiated and assessments performed at physician discretion per local standards of care. To reflect actual clinical practice, no assessments or procedures were required outside the standard of care. Patients who continued to receive long-term tolvaptan following hospital discharge and provided consent received follow-up from their community physicians.

Results

A total of 252 patients (mean age 70.6 years) enrolled. Mean tolvaptan treatment duration was 139.4 days, median 18.5 (range 1–1130) days; most frequent dose was 15 mg/day (used in 75% of patients). Serum sodium increased from baseline (mean 123.2 mmol/l) during treatment week 1 and remained stable during follow-up, with little difference across doses of 7.5, 15, and 30 mg/day. Hyponatremia symptoms (e.g., confusion, unsteady gait, lethargy) were present in 122/252 (48.4%) patients at pre-treatment baseline, decreasing to 46/252 (18.3%) during treatment. Sixty-two patients (24.6%; mean baseline serum sodium 120 mmol/l) experienced rapid correction of hyponatremia within 72 h. No osmotic demyelination syndrome occurred.

Conclusion

In clinical practice, tolvaptan improved serum sodium and decreased hyponatremia symptoms in hyponatremia secondary to SIADH. Serum sodium should be monitored during treatment to minimize risk of rapid correction.

Trial Registration

Clinicaltrials.gov identifier NCT01228682.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12325-021-01947-9.

Hospitalized patients often experience abnormally low blood sodium levels (hyponatremia), which can cause significant symptoms and poses a serious health risk (Wald et al. in Arch Intern Med 170:294–302, 2010). Yet, increasing sodium levels too rapidly in these patients can unintentionally cause osmotic demyelination syndrome, resulting in long-term neurologic damage or death. Tolvaptan was approved in the European Union to treat one type of hyponatremia caused by a hormonal imbalance known as the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Tolvaptan effectively increased patient sodium levels in clinical trials, but real-world data are needed to understand tolvaptan treatment more fully in everyday clinical practice. We evaluated patterns of use, efficacy, and safety of tolvaptan in patients treated in hospitals and after discharge for hyponatremia due to SIADH. Tolvaptan was correctly used to treat only hyponatremia caused by SIADH in nearly all of the 252 patients studied. Patient sodium levels increased in the first week of tolvaptan treatment and then stabilized. Hyponatremia symptoms, such as confusion, nausea, tiredness, and dizziness, were present in 48.4% of patients before treatment and in 18.3% after starting tolvaptan. Consistent with earlier studies, some patients (24.6%) experienced excessively rapid correction of hyponatremia. However, no subsequent neurologic problems or deaths were attributed to the rapid correction, which suggests that medical providers were carefully monitoring and managing sodium levels to prevent serious consequences. Our study indicates that tolvaptan is being used safely and effectively to treat hyponatremia due to SIADH in a patient population with complex medical needs.

Risk factors for sodium overcorrection in non-hypovolemic hyponatremia patients treated with tolvaptan

PURPOSE

In this study, the risk factors associated with sodium overcorrection were investigated with an optimal cutoff for baseline serum sodium for use in daily clinical practice.

METHODS

Electronic medical records of patients who received tolvaptan for non-hypovolemic hyponatremia were reviewed. Demographic and clinical data including age, sex, weight, height, comorbidity, cause of hyponatremia, hypertonic saline use, and comedication were collected. Baseline laboratory parameters measured included serum sodium, serum potassium, serum creatinine, blood urea nitrogen, serum tonicity, ALT, AST, and urine osmolality. The primary outcome was the overcorrection of serum sodium, which was defined as an increase in serum sodium by more than 10 mmol/L in 24 h.

RESULTS

From a total of 77 patients included in the analysis, 24 (31.2%) showed sodium overcorrection (> 10 mmol/L/24 h); 2 (2.6%) in heart failure cohort, 17 (22.1%) in SIADH cohort, and 5 (6.5%) in unknown cause cohort. More than half of patients (51.9%) were administered hypertonic saline prior to tolvaptan. Hypertension, cancer, diuretics, baseline serum sodium, and SIADH were associated with the risk of overcorrection in the univariable analysis. Significant factors for the overcorrection from multivariable analysis were lower body mass index, presence of cancer (adjusted odds ratio, 10.87; 95% CI, 1.23-96.44), and lower serum sodium at baseline (adjusted odds ratio, 0.76 for every 1 mEq/L increase; 95% CI, 0.61-0.94).

CONCLUSION

The overcorrection of hyponatremia in non-hypovolemic patients treated with tolvaptan was significantly associated with lower body mass index, presence of cancer, and lower serum sodium at baseline. In subgroup analysis using SIADH patients, baseline sodium and cancer were found to be significant factors of overcorrection.