The use of vasopressin receptor antagonists in hyponatremia

INTRODUCTION: Considerable data have recently characterized hyponatremia as fairly common in the intensive care and general hospital settings. Moreover, mounting evidence suggests the association of mild degrees of hyponatremia with untoward neurocognitive and musculoskeletal outcomes. A key development in our ability to treat hyponatremia was the introduction and approval of aquaretics (vaptans). These vasopressin receptor antagonists work by increasing electrolyte-free water excretion and thus raising serum sodium concentration. AREAS COVERED: This review presents a diagnostic approach for hyponatremia and discusses some therapeutic considerations. It displays new evidence linking mild chronic hyponatremia with unfavorable outcomes and examines the available treatment options and their limitations and strengths. New data on vaptans and their potential role to treat hyponatremia in different clinical settings are reviewed. EXPERT OPINION: Vaptans are likely to play an important role in treating hyponatremia, given their clinical efficacy and tolerability. High cost remains an impediment for vaptans, and more studies are needed to further define their best use in hyponatremic patients.     

Tolvaptan: a vasopressin antagonist for the management of euvolemic and hypervolemic hyponatremia

Tolvaptan is a new vasopressin antagonist developed for the treatment of hypervolemic or euvolemic hyponatremia. It has greater affinity for the V₂ receptor than native vasopressin or any other vasopressin antagonist. Blockade of the V₂ receptor induces solute-free water excretion without affecting normal electrolyte excretion. The pharmacokinetics and pharmacodynamics of tolvaptan are suitable for once-daily dosing. Throughout all phases of clinical studies, it was shown to be safe for short- and long-term use. Tolvaptan effectively increases serum sodium levels in patients with heart failure, cirrhosis and syndrome of inappropriate secretion of antidiuretic hormone. In patients hospitalized owing to heart failure, tolvaptan decreased bodyweight, increased urine output and improved dyspnea compared with placebo. However, tolvaptan has not proven to be beneficial for the long-term management of heart failure. Currently, tolvaptan is the only oral agent in its class available in the USA and Europe.     

Treatment of hyponatremia: the role of lixivaptan

Hyponatremia is the most common electrolyte disorder and is associated with serious neurologic sequelae and increased mortality. Conventional treatment options for hyponatremia, such as fluid restriction, hypertonic saline, loop diuretics, demeclocycline or urea, are ineffective in the long-term. The present review considers the role of vasopressin receptor inhibitors (vaptans), focusing on lixivaptan, in the treatment of patients with euvolemic or hypervolemic hyponatremia. Lixivaptan is an oral selective V2 receptor inhibitor, which produces a significantly greater increase of serum sodium levels compared with placebo. These effects seem promising, but more trials are needed to examine whether the beneficial effect of lixivaptan on serum sodium concentration translates into clinical benefit in these patient populations.     

Lixivaptan: a novel vasopressin receptor antagonist

Arginine vasopressin, also known as antidiuretic hormone, is a neuropeptide that functions in the maintenance of body water homeostasis. Inappropriate secretion of vasopressin has been implicated in the pathophysiology of multiple diseases, including polycystic kidney disease, syndrome of inappropriate antidiuretic hormone (SIADH) secretion, and the hyponatremia commonly associated with cirrhosis and congestive heart failure. Vasopressin receptor antagonists are novel agents that block the physiologic actions of vasopressin. Lixivaptan is a vasopressin receptor antagonist with high V2 receptor affinity and is now undergoing Phase III clinical trials. Studies so far have demonstrated that lixivaptan is efficacious in the correction of hyponatremia in SIADH, heart failure and liver cirrhosis with ascites, and few adverse effects have been noted. Thus, lixivaptan remains a promising therapeutic modality for the treatment of multiple diseases and prevention of the associated morbidity and mortality associated with hyponatremia.     

Vasopressin receptor antagonists in the management of acute heart failure

Vasopressin is a potent vasoconstrictor and plays a significant role in the regulation of volume homeostasis. Several non-peptide vasopressin receptor antagonists (vaptans) have emerged as promising drugs in the management of acute heart failure. Results of early trials with tolvaptan (selective vasopressin subtype 2 receptor antagonist) and conivaptan (dual vasopressin subtypes 1a and 2 receptor antagonist) have demonstrated improvement in the fluid status, osmotic balance and haemodynamic profile in patients with heart failure presenting with signs and symptoms of decompensation. Nevertheless, their comparative long-term safety and efficacy remains to be determined in large-scale clinical trials.     

Recent advances in the treatment of hyponatremia

Hyponatremia is a common and potentially serious electrolyte disorder, most often caused by excessive arginine vasopressin (AVP) secretion. Conventional management of hyponatremia is based on graded steps starting from water restriction in mild cases to administration of saline in symptomatic cases, which may not be effective. A major new approach in the treatment of hyponatremia is the development of AVP receptor antagonists that directly inhibit the effect of increased AVP which results in the excretion of electrolyte free water. This review summarizes pathophysiology, conventional treatment and future directions in the treatment of hyponatremia.     

Vasopressin receptor antagonists in the management of acute heart failure

Vasopressin is a potent vasoconstrictor and plays a significant role in the regulation of volume homeostasis. Several non-peptide vasopressin receptor antagonists (vaptans) have emerged as promising drugs in the management of acute heart failure. Results of early trials with tolvaptan (selective vasopressin subtype 2 receptor antagonist) and conivaptan (dual vasopressin subtypes 1a and 2 receptor antagonist) have demonstrated improvement in the fluid status, osmotic balance and haemodynamic profile in patients with heart failure presenting with signs and symptoms of decompensation. Nevertheless, their comparative long-term safety and efficacy remains to be determined in large-scale clinical trials.     

Tolvaptan for the treatment of heart failure: a review of the literature

Introduction: It has been > 25 years since it was first discovered that arginine vasopressin levels are elevated in heart failure and this elevation is proportional to the severity of heart failure. Tolvaptan is an oral nonpeptide V₂-selective antagonist and has been shown to induce free water excretion without increasing urine sodium, an effect termed ‘aquaresis’.

Areas covered: This paper aims to review the physiology, chemistry, pharmacokinetics, clinical efficacy and safety of tolvaptan in HF. A PubMed literature search was performed using ‘tolvaptan’ and the MeSH term ‘heart failure’, yielding 89 references.

Expert opinion: Clinical trials conducted in ambulatory and hospitalized patients with HF have found treatment with tolvaptan causes rapid and sustained body weight reductions concurrent with increases in urine output, improves and/or normalizes serum sodium in hyponatremic patients, reduces signs and symptoms of congestion and increases thirst. However, tolvaptan has not been shown to decrease HF re-hospitalization or mortality. As an adjunct to standard therapy, tolvaptan is unique in that it is virtually the only novel agent tested in patients hospitalized for acute heart failure syndrome (AHFS) to reach its primary end point for short-term efficacy without causing deleterious side effects. There is theoretical concern that chronic V₂ receptor blockade may cause harmful long-term side effects via enhanced V_1a receptor activation, potentially offsetting any favorable effects on congestion and hyponatremia. The ‘vaptan’ class of drugs is an active and promising area for clinical investigation and future research is necessary to clarify the therapeutic role of selective and nonselective vasopressin inhibition in chronic HF and AHFS.     

Effect of Experimental Renal Failure and Hypotonic Hyponatremia on the Pharmacodynamics of Cefazolin-Induced Seizures in Rats

Purpose. The purpose of this study was to investigate the effect of experimental renal failure and hypotonic hyponatremia on the pharmacodynamics of cefazolin (CEZ)-induced seizures. Methods. Rats received an intravenous infusion of CEZ until the onset of seizures. Renal failure was produced by bilateral ureteral ligation (UL) or uranyl nitrate (UN) injection. Hypotonic hyponatremia was produced by intravenous infusion of 5% dextrose in water or intraperitoneal infusion of distilled water after arginine vasopressin injection. Results. The serum and brain concentrations of CEZ at the onset of seizures increased with increasing infusion rate, but the CSF concentration of CEZ at the onset of seizures was not affected by the infusion rate. The concentration of CEZ in CSF at the onset of seizures was significantly lower in UL rats than control rats, whereas there was no difference between UN rats and their controls. Serum concentrations of Na⁺ and serum tonicity were lower in UL rats than UN rats. Hypotonic hyponatremia had no apparent effect on the CSF concentration of CEZ. The CSF concentration of CEZ at the onset of seizures was significantly lower in UN rats with hypotonic hyponatremia than their controls. Conclusions. Renal failure with severe hypotonic hyponatremia is associated with increased central nervous system sensitivity to CEZ-induced seizures.     

Safety of neurokinin-1 receptor antagonists

Introduction: The substance P (SP)/neurokinin (NK)-1 receptor system is involved in many pathological processes. NK-1 receptor antagonists have many promising therapeutic indications. However, the only NK-1 receptor antagonist used in clinical practice is the drug aprepitant and its intravenously administered prodrug, fosaprepitant. In general, NK-1 receptor antagonists are safe and well tolerated.

Areas covered: A search was carried out in Medline using the following terms: adverse events, aprepitant, casopitant, clinical trials, CP-122,721, ezlopitant, fosaprepitant, NK-1 receptor antagonists, randomized, safety, side effects, tolerability and vofopitant.

Expert opinion: Most clinical trials have focused on the antiemetic action of aprepitant in cancer patients treated with chemotherapy. However, the efficacy and safety of aprepitant have not been fully tested in other diseases in which the SP/NK-1 receptor system is involved (e.g., cancer, HIV, alcoholism); thus, clinical trials are required. The use of NK-1 receptor antagonists in oncology therapy is quite promising, but to date pharmacological therapy has not exploited the many possible therapies offered by such antagonists.     

Vasopressin receptor antagonists in heart failure

Vasopressin receptor antagonists are a new class of drugs that address the problems of fluid retention, hyponatremia, and renal dysfunction in heart failure. Elevated vasopressin levels in heart failure cause myocardial fibrosis, hypertrophy and vasoconstriction by activating the V1a receptors, as well as water retention and hyponatremia by activating V2 receptors. Antagonism of V1a receptors alone is of little benefit. In contrast, antagonism of V2 receptors results in increased free water excretion and increased sodium concentration. Vasopressin receptor antagonists may be viewed as the first new class of agents with predominantly aquaretic effects, in contrast to the natriuretic effects of loop diuretics. The predominant action of vasopressin receptor antagonists is water excretion, without depletion of other electrolytes, and less neurohormonal stimulation compared with loop diuretics. Classified as neurohormonal antagonists, vasopressin receptor antagonists acutely may improve congestion and hyponatremia, while chronically preventing progression of left ventricular dysfunction. Several compounds have been evaluated in late-stage clinical trial programs, and at least one may be used as an adjunct to standard medical therapy, combining aquaresis for congestion with neurohormonal antagonism for morbidity and mortality. We reviewed recent patents dealing with heart failure, hyponatremia, anti-diuretic hormone, and vasopressin antagonists.     

New agents for managing hyponatremia in hospitalized patients.

PURPOSE: An overview of hyponatremia is provided, including its pathophysiology, clinical manifestations, signs and symptoms, and treatment, particularly with arginine vasopressin (AVP)-receptor antagonists. SUMMARY: Hyponatremia (generally defined as a serum sodium concentration of <135 meq/L) is one of the most common electrolyte disorders in hospitalized and clinic patients. It may be caused by a number of conditions, including infections, heart disease, surgery, malignancy, and medication use. Clinical signs and symptoms such as hallucinations, lethargy, weakness, bradycardia, respiratory depression, seizures, coma, and death have been reported. Conventional treatment consists of fluid restriction and administration of hypertonic saline and pharmacologic agents, such as demeclocycline, lithium carbonate, and urea. These treatment options are often of limited effectiveness or difficult for patients to tolerate. AVP promotes the reabsorption of water in the renal collecting ducts by activation of V(2) receptors, resulting in water retention and dilution of serum solutes. The AVP-receptor antagonists, conivaptan, lixivaptan, and tolvaptan, are being studied for the treatment of hyponatremia. Conivaptan has been shown in clinical trials to increase free-water excretion and safely normalize serum sodium concentrations in patients with hyponatremia and is well tolerated. Also in clinical trials, lixivaptan and tolvaptan have safely improved serum sodium concentrations in patients with hyponatremia. CONCLUSION: Hyponatremia is a serious health condition for which treatment should be carefully performed. As new agents for treating hyponatremia, AVP-receptor antagonists have demonstrated efficacy and safety in clinical trials and may serve as significant improvements in the current treatment options for managing this disorder.     

Hyponatremia induced by antiepileptic drugs in patients with epilepsy

Introduction: Hyponatremia induced by antiepileptic drugs (AEDs) has not received sufficient attention in patients with epilepsy.

Areas covered: We reviewed articles between 1966 and 2015 about hyponatremia as an adverse effect of AEDs in patients with epilepsy. The incidence, clinical symptoms, onset times of AEDs-induced hyponatremia are discussed in detail, as are the risk factors associated with AEDs-induced hyponatremia and mechanisms underlying its development. We also briefly describe strategies for treating AED-induced hyponatremia.

Expert opinion: Carbamazepine and oxcarbazepine are the most common AEDs which induce hyponatremia in patients with epilepsy. Recently, other AEDs, such as eslicarbazepine, sodium valproate, lamotrigine, levetiracetam and gabapentin have also been reported to cause hyponatremia. Understanding the risk associated with AED-induced hyponatremia and taking effective measures to combat serum sodium imbalance induced by AED therapy are necessary.     

Tolvaptan: a vasopressin antagonist for the management of euvolemic and hypervolemic hyponatremia

Tolvaptan is a new vasopressin antagonist developed for the treatment of hypervolemic or euvolemic hyponatremia. It has greater affinity for the V(2) receptor than native vasopressin or any other vasopressin antagonist. Blockade of the V(2) receptor induces solute-free water excretion without affecting normal electrolyte excretion. The pharmacokinetics and pharmacodynamics of tolvaptan are suitable for once-daily dosing. Throughout all phases of clinical studies, it was shown to be safe for short- and long-term use. Tolvaptan effectively increases serum sodium levels in patients with heart failure, cirrhosis and syndrome of inappropriate secretion of antidiuretic hormone. In patients hospitalized owing to heart failure, tolvaptan decreased bodyweight, increased urine output and improved dyspnea compared with placebo. However, tolvaptan has not proven to be beneficial for the long-term management of heart failure. Currently, tolvaptan is the only oral agent in its class available in the USA and Europe.     

NK-1 receptor antagonists as antitumor drugs: a survey of the literature from 2000 to 2011

Introduction: After binding to the neurokinin (NK-1) receptor, substance P (SP) induces tumor cell proliferation, the migration of tumor cells (invasion and metastasis) and angiogenesis. By contrast, NK-1 receptor antagonists inhibit tumor cell proliferation (tumor cells die by apoptosis), block the migratory activity of tumor cells and exert antiangiogenic properties.

Areas covered: This review offers a 12-year overview of the underlying mechanism of the action of the SP/NK-1 receptor system and NK-1 receptor antagonists in cancer, providing a new approach to the treatment of tumors.

Expert opinion: Chemically diverse NK-1 receptor antagonists have been identified. The antitumor action of these compounds is independent of their chemical structures and such action is associated with their affinity for the NK-1 receptor and with the dose of the antagonist administered. The NK-1 receptor can be considered as a target in cancer treatment and NK-1 receptor antagonists could be considered as new antitumor drugs. The NK-1 receptor antagonist aprepitant is used in clinical practice and exerts an antitumor action against tumor cells in vitro. In the future, such antitumor action should be tested in human clinical trials.     

CGRP receptor antagonists: design and screening

Importance of the field: Calcitonin gene-related peptide (CGRP) receptor antagonists have recently come to attention with the development of olcegepant and telcagepant for the treatment of migraine. The availability of high-affinity, non-peptide antagonists opens the way for trials of these compounds in other conditions where CGRP antagonism might be useful, such as septic shock and inhibition of angiogenesis.

Areas covered in this review: This review summarises knowledge about the structure and signalling properties of the CGRP receptor. The clinical ramifications of targeting the CGRP receptor, the profiles of existing antagonists and the requirements for screening new compounds will be discussed.

What the reader will gain: Readers will gain an overview of how current non-peptide antagonists seem to bind similar epitopes contributed by both calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein 1 (RAMP1), the main CGRP receptor subunits. We will discuss how current antagonists have low bioavailability, limiting their use. For selectivity at CGRP receptors, it will be necessary to target parts of the receptor influenced by both RAMP1 and CLR.

Take home message: For the design of radically new antagonists, more structural information on the receptor is needed. Current screens are largely based on measuring CGRP-mediated changes in cAMP. CGRP receptors can influence other signalling pathways and pathway-selective allosteric antagonists may be useful, but more information is needed about the mechanism of action of CGRP to assess the value of this.     

Challenges in the management of asthma associated with smoking-induced airway diseases

ABSTRACT

Introduction: Smoking-induced airway diseases such as chronic bronchitis, emphysema, and small airway dysfunction contribute to the chronic respiratory symptoms experienced by adults with asthma, including those with spirometric chronic obstructive pulmonary disease (COPD), termed asthma-COPD overlap (ACO). Drug treatment of symptomatic smokers with asthma or ACO is uncertain due to their exclusion from most clinical trials.

Areas covered: This review summarizes evidence for the efficacy of small molecule drugs used in the clinic to treat current and former smokers with a diagnostic label of asthma or ACO. Other therapeutic interventions are reviewed, including smoking cessation and biologics.

Expert opinion: Clinical trials and observational studies suggest that smoking cessation and approved drugs used to treat non-smokers with asthma produce clinical benefits in smokers with asthma or ACO, although the overall quality of evidence is low. The efficacy of some treatments for asthma is altered in current smokers, including reduced responsiveness to short-term inhaled corticosteroids and possibly improved responsiveness to leukotriene receptor antagonists. Preliminary findings suggest that low-dose theophylline, statins, and biologics, such as omalizumab, mepolizumab, and dupilumab, may improve clinical outcomes in smokers with asthma or ACO. Improved phenotyping and endotyping of asthma and smoking-induced airway diseases should lead to better targeted therapies.     

Opioid antagonists for pain

Introduction: Opioid receptor antagonists are well known for their ability to attenuate or reverse the effects of opioid agonists. This property has made them useful in mitigating opioid side effects, overdose and abuse. Paradoxically, opioid antagonists have been reported to produce analgesia or enhance analgesia of opioid agonists. The authors review the current state of the clinical use of opioid antagonists as analgesics.

Areas covered: Published clinical trials, case reports and other sources were reviewed to determine the effectiveness and safety of opioid antagonists for use in relieving pain. The results are summarized. Postulated mechanisms for how opioid antagonists might exert an analgesic effect are also briefly summarized.

Expert opinion: Since the comprehensive review by Leavitt in 2009, few new studies on the use of opioid antagonists for pain have been published. The few clinical trials generally consist of small populations. However, there does appear to be a trend of effectiveness of low doses (higher doses antagonize opioid agonist effects). How opioid antagonists can elicit an analgesic effect is still unclear, but a number of possibilities have been suggested. Although the data do not yet support recommendation of widespread application of this off-label use of opioid antagonists, further study appears worthwhile.     

Conivaptan: promise of treatment in heart failure

Conivaptan, the first vasopressin receptor antagonist approved by the FDA, is available for the treatment of hyponatremia in euvolemic and hypervolemic patients. The renin-angiotensin-aldosterone system is activated in heart failure (HF) causing clinical worsening. Arginine vasopressin levels are also elevated in HF. Conivaptan is an effective and FDA approved for the treatment of euvolemic and hypervolemic hyponatremia and may offer an extra treatment option in HF by targeting V_1a and V₂ receptors. In this article we review the physiology, preclinical studies as well as the human clinical studies on the use of conivaptan and its potential and promise in the treatment of HF.     

Pharmacological management of hyponatremia

Introduction: Hyponatremia is the most common electrolyte disorder with a prevalence of up to 30% in hospitalized patients. Furthermore, it is associated with increased morbidity and mortality.

Areas covered: This review discusses the efficacy and side effects of the currently available treatment options for hyponatremia and the differences in the pharmacological approach between the European and USA guidelines. Additionally, the authors provide their expert perspectives on current treatment strategies and what they expect from this field in the future.

Expert opinion: Several pharmacological options are available for the treatment of hyponatremia, but data from trials examining and comparing these treatments are missing. Regarding chronic hyponatremia, the role of vaptans should be further analyzed, focusing on comparisons with other active treatments on patient-relevant outcomes and not only on serum sodium concentration. Clinicians should be cautious to an overly rapid increase in serum sodium levels with all available treatment strategies. Finally, it is important to ascertain whether correction of serum sodium levels improves mortality in hyponatremic patients.