Hyponatremia: current treatment strategies and the role of vasopressin antagonists

In-patient Tolvaptan use in SIADH: care audit, therapy observation and outcome analysis

BACKGROUND

Indications for use of tolvaptan in SIADH-associated hyponatraemia remain controversial. We audited our local guidelines for Tolvaptan use in this situation to review treatment implications including drug safety, hospital admission episode analysis (episodes of liver toxicity, CNS myelinolysis, sodium-related re-admission rates), morbidity; mortality and underlying aetiologies.

METHODS

We report a retrospective case series analysis of on-going treatment outcomes (case-note review) for 31 patients (age 73.3 ± 10.5 years, 55% females) consecutively treated with Tolvaptan as in-patient for confirmed SIADH with persistent S/Na⁺ < 125 mmol/L despite removal of reversible causes and 24-48 h fluid restriction, and include longer-term outcome data (re-treatment/readmissions/mortality) for up to 4 years of follow-up. A minimum of 6 months follow-up data were reviewed unless the patient died before that period.

RESULTS

Short-term outcomes were favourable; 94%-achieved treatment targets after a mean of 3.48 ± 2.46 days. There was statistically significant rise in S/Na⁺ level after Tolvaptan treatment (before treatment: mean sodium 117.8 ± 3.73, 108-121 mmol/L and after treatment: mean sodium 128.7 ± 3.67, 125-135.2 mmol/L, P < .001). Although the target S/Na⁺ level was >125 mmol/L in fact one third (35%) of the patients achieved a S/Na⁺ level of >130 mmol/L by the time of hospital discharge. No patient experienced S/Na⁺ rise >12 mmol/L/24 h, drug-associated liver injury or CNS-myelinolysis. The average length of hospital stay following start of Tolvaptan treatment was 3.2 days. Relapse of hyponatraemia occurred in 26% of the patients, requiring retreatment with Tolvaptan. In all patients where either relapse of hyponatraemia occurred or readmission was necessary, SIADH was associated with malignancy, which was present overall in 60% of the group studied.

CONCLUSIONS

This study confirms the safety and efficacy of Tolvaptan in the treatment of SIADH-related significant, symptomatic hyponatraemia when used under specialist guidance and strict monitoring. A sodium level relapsing below the treatment threshold by 1 week after discontinuation is a good indicator of a patient group with re-treatment/longer-term therapy needs, all of whom had underlying malignancy. The criteria set locally in our trust to initiate Tolvaptan use also identifies a group where further investigation for underlying malignancy should be considered.

Management of hyponatraemia in older people: old threats and new opportunities

Hyponatraemia is the commonest electrolyte abnormality seen in clinical practice, and is especially prevalent in frail, older people. However, the serious implications of hyponatraemia in this age group are seldom recognized by clinicians. Hyponatraemia is associated with osteoporosis, impaired balance, falls, hip fractures and cognitive dysfunction. Even mild, apparently asymptomatic hyponatraemia is associated with prolonged stays in hospital, institutionalization and increased risk of death. Emerging evidence of the potential benefits of improved treatment of hyponatraemia is slowly generating renewed clinical interest in this area. The development of specific vasopressin-2 receptor antagonists (vaptans) has the potential to revolutionize the management of hyponatraemia, in particular for the syndrome of inappropriate antidiuretic hormone. However, challenges remain for the attending physician. Diagnosing the cause or causes of hyponatraemia in older people is difficult, and incorrect diagnosis can lead to treatment that worsens the electrolyte imbalance. Established treatments are often poorly tolerated and patient outcomes remain poor, and the role of vaptans in the treatment of older people is unclear. This review summarizes the existing evidence base and highlights areas of controversy. It includes practical guidance for overcoming some common pitfalls in the management of the elderly patient with hyponatraemia.

Novel treatment targets for cerebral edema

Cerebral edema is a common finding in a variety of neurological conditions, including ischemic stroke, traumatic brain injury, ruptured cerebral aneurysm, and neoplasia. With the possible exception of neoplasia, most pathological processes leading to edema seem to share similar molecular mechanisms of edema formation. Challenges to brain-cell volume homeostasis can have dramatic consequences, given the fixed volume of the rigid skull and the effect of swelling on secondary neuronal injury. With even small changes in cellular and extracellular volume, cerebral edema can compromise regional or global cerebral blood flow and metabolism or result in compression of vital brain structures. Osmotherapy has been the mainstay of pharmacologic therapy and is typically administered as part of an escalating medical treatment algorithm that can include corticosteroids, diuretics, and pharmacological cerebral metabolic suppression. Novel treatment targets for cerebral edema include the Na(+)-K(+)-2Cl(-) co-transporter (NKCC1) and the SUR1-regulated NC(Ca-ATP) (SUR1/TRPM4) channel. These two ion channels have been demonstrated to be critical mediators of edema formation in brain-injured states. Their specific inhibitors, bumetanide and glibenclamide, respectively, are well-characterized Food and Drug Administration-approved drugs with excellent safety profiles. Directed inhibition of these ion transporters has the potential to reduce the development of cerebral edema and is currently being investigated in human clinical trials. Another class of treatment agents for cerebral edema is vasopressin receptor antagonists. Euvolemic hyponatremia is present in a myriad of neurological conditions resulting in cerebral edema. A specific antagonist of the vasopressin V1A- and V2-receptor, conivaptan, promotes water excretion while sparing electrolytes through a process known as aquaresis.

Hyponatremia's Impact on Patients and Health Systems

Purpose

To define hyponatremia, discuss its incidence and epidemiology, and summarize the frequency and prognostic implications of hyponatremia in selected clinical conditions.

Summary

Hyponatremia is the most common electrolyte abnormality encountered in clinical practice. Hyponatremia is commonly defined as a serum sodium concentration of <136 mEq/L. There are 3 different types of hyponatremia: hypovolemia, euvolemia, and hypervolemia. Epidemiologic studies reveal that hyponatremia is a common problem in hospitalized patients whether it is present at admission or is hospital acquired. The disorder increases the risk of admission to the intensive care unit, hospital length of stay, and morbidity and mortality. Hyponatremia appears to be a marker for severe underlying disease with a poor prognosis. Congestive heart failure, pneumonia, cirrhosis, and neurologic disease are among the serious clinical conditions known to be associated with hyponatremia. Chronic hyponatremia presents its own set of challenges; even in mild disease that is often asymptomatic, patients are at heightened risk for falls, gait disturbances, attention deficits, and fracture.

Conclusion

Hyponatremia is the most common electrolyte disorder encountered in clinical practice and is associated with significant morbidity and mortality, especially at lower serum sodium concentrations. The disorder has a substantial impact on hospital length of stay with a direct impact on health care costs. Further, as this discussion illustrates, hyponatremia represents a significant clinical burden in all forms – mild, moderate, and severe – with subsequent clinical consequences.

Cost Issues in Hyponatremia

Purpose

To describe the morbidity and mortality associated with hyponatremia and its impact on health care costs and outcomes in the United States, describe the role of pharmacists in the overall management of hyponatremia, and identify and address cost and resource allocation issues.

Summary

Hyponatremia places a significant burden on overall hospital and health care costs. Underrecognition of the disorder and inappropriate hospital management can lead to worse outcomes, impacting length of stay (LOS), need for intensive care unit (ICU) admission, and clinical outcomes. Risk of mortality rises with increasing severity of hyponatremia, but even mild hyponatremia is associated with increased in-hospital mortality. The association with mortality is particularly robust in patients admitted to the hospital with cardiovascular disease and metastatic cancer. For patients admitted to the ICU, severe hyponatremia is a predictor of mortality. Elderly patients with admission hyponatremia face an especially poor prognosis. Resolving hyponatremia during hospitalization decreases the risk of mortality, suggesting that improved identification and aggressive monitoring may lead to more appropriate treatment. Pharmacoeconomic data can be utilized to support clinical decision-making in the management of hyponatremia by evaluating drug therapy and by monitoring hyponatremia development and therapeutic outcomes.

Conclusion:

Prompt recognition and optimal management of hyponatremia in hospitalized patients may reduce mortality and symptom severity, allow for less intensive care, decrease LOS and associated costs, and improve treatment of underlying comorbid conditions and quality of life. Pharmacists have a key role in optimizing the management of hyponatremia.

Tolvaptan

Tolvaptan is an orally administered, nonpeptide, selective arginine vasopressin V(2) receptor antagonist that increases free water clearance, thereby correcting low serum sodium levels. SALT-1 and -2, two identical, randomized, double-blind, placebo-controlled, multicentre trials, included patients with hypervolaemic or euvolaemic hyponatraemia (serum sodium <135 mmol/L) associated with heart failure, cirrhosis or the syndrome of inappropriate antidiuretic hormone secretion. In both trials, patients receiving (in addition to standard medical treatment) tolvaptan 15-60 mg once daily (titrated according to response) for up to 30 days (n = 95 and 118) experienced significantly greater improvements than those receiving placebo (n = 89 and 114) for the co-primary endpoints of the change in average daily area under the curve for the serum sodium level from baseline to day 4 and from baseline to day 30. This beneficial effect of tolvaptan on serum sodium levels in SALT-1 and -2 was observed in patients with mild (serum sodium <135 mmol/L) and in those with marked (serum sodium <130 mmol/L) hyponatraemia at baseline. Tolvaptan was also superior to placebo in increasing serum sodium levels from baseline to day 7 in a subgroup of 323 patients with hyponatraemia (serum sodium <134 mmol/L) in the randomized, double-blind, multicentre EVEREST trials, which included patients who were hospitalized for worsening heart failure. Tolvaptan was generally well tolerated in clinical trials. The most frequently reported adverse events were thirst and dry mouth, which result from the pharmacodynamic effects of the drug.

A different hypothesis on hyponatremia in psychiatric patients: treatment implications and experiences

Polydipsia, chronic or intermittent, with or without hyponatremia, frequently occurs among chronic patients with schizophrenia. The pathogenesis of polydipsia remains poorly understood. The key assumption of our hypothesis is that in some of these patients, polydipsia and hyponatremia are consequences of patients' adjustment to a prolonged intake of an insufficient diet, dominantly poor in potassium. Deficits of potassium, without significant hypokalemia, may cause impairment of the urine-concentrating ability with polyuria-polydipsia. A fall of intracellular tonicity, dominantly due to a decreased amount of K(+) and attendant anions in cells, should be accompanied with a fall of extracellular osmolality. Because of the diminished content of ions that may diffuse out of cells and because osmotic equilibrium between the ECF and ICF compartments cannot be established in a short period of time, these patients have a diminished ability to adapt to an excessive intake of fluids. These mechanisms might be related to the development of polydipsia and water intoxication in patients with different mental and somatic disorders. The experiences with the therapeutic effects of diets containing an sufficient amount of potassium in two patients with schizophrenia are described. Further investigations are needed, and we suggest a possible approach to test our hypotheses.

Conivaptan bolus dosing for the correction of hyponatremia in the neurointensive care unit

INTRODUCTION

Hyponatremia frequently complicates acute brain injury and may precipitate neurological worsening by promoting cerebral edema. An increase in brain water may be better managed through water excretion than with fluid restriction or hypertonic fluids. Vasopressin-receptor antagonists such as conivaptan, which promote free water excretion, may be ideal agents to treat this common and potentially serious disorder.

METHODS

The efficacy of intermittent bolus doses of conivaptan to correct hyponatremia was examined in a consecutive series of patients treated in our neurointensive care unit. Patients were excluded if baseline sodium was over 135 mEq/l or if another conivaptan dose was given within 12 h. We assessed the proportion responding with a 4 or 6 mEq/l rise in sodium by 12 h, the change in sodium from baseline, and, in those not receiving another dose for at least 72 h, the long-term ability of a single dose to maintain sodium at least 4 mEq/l above baseline. We also recorded the effects of conivaptan on urine output and specific gravity, and noted any adverse events.

RESULTS

A total of 25 doses given to 19 patients were included (out of 44 total doses administered in the study period). Sodium rose by 5.8 +/- 3.2 mEq/l within 12 h, with 71% rising by at least 4 mEq/l and 52% manifesting at least a 6 mEq/l increase. In those receiving only a single dose, 69% maintained at least a 4 mEq/l rise up to 72 h. Conivaptan also consistently led to increased urine output and a significant drop in urine specific gravity (i.e., aquaresis). No cases of phlebitis were observed despite administration of conivaptan through peripheral IVs.

CONCLUSION

Intermittent dosing of conivaptan was effective in increasing free water excretion and correcting hyponatremia in neurologically ill patients. This supports its further evaluation for managing hyponatremia in this population.

Hyponatremia in psychiatric patients: update on evaluation and management

BACKGROUND

Hyponatremia (serum sodium concentration < 136 mEq/L) is a prevalent and potentially dangerous medical comorbidity in psychiatric patients.

METHODS

MEDLINE was used to identify peer-reviewed publications that described the role of arginine vasopressin (AVP) in the pathogenesis of hyponatremia, the presentation and treatment of hyponatremia in psychiatric patients, and promising new treatment options.

RESULTS

Polydipsia may lead to hyponatremia in patients with schizophrenia, which is mediated, in part, by a reduced osmotic threshold for the release of AVP and by a defect in the osmoregulation of thirst. Acute-onset hyponatremia may require emergent treatment with hypertonic (3%) saline, whereas chronic cases mandate gradual correction to minimize the risk of osmotic demyelination. The AVP-receptor antagonists, including conivaptan, tolvaptan, lixivaptan, and satavaptan, represent a therapeutic advance in the treatment of dilutional hyponatremia.

CONCLUSION

Based on the role of AVP in the development of hyponatremia, further studies are warranted to determine the efficacy of the AVP-receptor antagonists in psychiatric patients with hyponatremia.