Evaluation and management of hyponatremia: an emerging role for vasopressin receptor antagonists

Ratio Profile: Physiologic Approach to Estimating Appropriate Intravenous Fluid Rate to Manage Hyponatremia in the Syndrome of Inappropriate Antidiuresis

A hyponatremic patient with the syndrome of inappropriate antidiuresis (SIAD) gets normal saline (NS), and the plasma sodium decreases, paradoxically. To explain, desalination is often invoked: if urine is more concentrated than NS, the fluid's salts are excreted while some water is reabsorbed, exacerbating hyponatremia. But comparing concentrations can be deceiving. They should be converted to quantities because mass balance is key to unlocking the paradox. The [sodium] equation can legitimately be used to track all of the sodium, potassium, and water entering and leaving the body. Each input or output "module" can be counterbalanced by a chosen iv fluid so that the plasma sodium stays stable. This equipoise is expressed in terms of the iv fluid's infusion rate, an easy calculation called the ratio profile. Knowing the infusion rate that maintains steady state, we can prescribe the iv fluid at a faster rate in order to raise the plasma sodium. Rates less than the ratio profile may risk a paradox, which essentially is caused by an iv fluid underdosing. Selecting an iv fluid that is more concentrated than urine is not enough to prevent paradoxes; even 3% saline can be underdosed. Drinking water adds to the ratio profile and is underestimated in its ability to provoke a paradox. In conclusion, the quantitative approach demystifies the paradoxical worsening of hyponatremia in SIAD and offers a prescriptive guide to keep the paradox from happening. The ratio profile method is objective and quickly deployable on rounds, where it may change patient management for the better.

Efficacy of vasopressin V2 receptor antagonist tolvaptan in treatment of hepatic edema

AIM

Tolvaptan, an oral active vasopressin V2 receptor antagonist, is widely used for hepatic edema in Japan, but its clinical benefits have yet to be fully clarified. The present study evaluated the efficacy of tolvaptan in hepatic edema.

METHODS

The efficacy and treatment regimen of tolvaptan were evaluated in 150 patients with hepatic edema by analyzing the initial (day 14) and long-term (day 90) responses to the drug and their predictive factors. All patients were divided into good (Child-Pugh classification B, and absent of advanced hepatocellular carcinoma) and poor hepatic condition groups, and the response rates were compared between the two groups.

RESULTS

The initial response rate was 62%, and the long-term response rate was 47%. The assessment of predictive factors for response to tolvaptan showed that serum creatinine and C-reactive protein levels were important predictors of initial response, and that hepatic conditions, such as the Child-Pugh score or presence of hepatocellular carcinoma, as well as initial response, were significant predictors of long-term response. In addition, both the initial and long-term response rates and the cumulative survival rate were found to be higher in the good hepatic condition group than in the poor hepatic condition group, respectively (71% vs. 57%, P = 0.113; 62% vs. 39%, P = 0.009; log-rank test, P < 0.001).

CONCLUSION

These results suggest that tolvaptan may provide high response rates when used early in the course of hepatic edema, or when both hepatic and renal functions are still retained, leading to an improved disease prognosis.

Characterization of the stress degradation products of tolvaptan by UPLC-Q-TOF-MS/MS

TVT was subjected to forced degradation under hydrolysis, oxidation, dry heat and photolysis conditions and the degradation products (DPs) formed have been characterized through UPLC-PDA and UPLC-Q-TOF-MS/MS studies.

Tolvaptan for the treatment of hyponatremia and hypervolemia in patients with congestive heart failure

Patients with heart failure often show increased arginine vasopressin secretion and enhanced sympathetic and renin-angiotensin-aldosterone activation, which accelerate renal water reabsorption, causing water retention and volume overload. Tolvaptan is an orally active antagonist of arginine vasopressin type 2 receptors in the collecting duct of the kidney that inhibits water reabsorption without substantially affecting the electrolyte balance. Tolvaptan in combination with conventional diuretics improves fluid retention and congestive symptoms in patients with heart failure and volume overload, with minimal effects on hemodynamics and serum potassium. Tolvaptan slightly increases serum sodium concentrations, generally within the normal range. Although it does not seem to affect long-term mortality, tolvaptan does improve short-term water retention and congestive symptoms in heart failure patients with volume overload despite the use of conventional diuretics, and is approved for this indication in Japan.

Vasopressin receptor antagonists and their role in clinical medicine

Hyponatremia is the most common electrolyte abnormality in hospitalized patients. Its treatment is based not only on extracellular fluid volume status of patients but also on its pathogenetic mechanisms. Conventional treatment of hyponatremia like fluid restriction, which is useful in euvolemic and hypervolemic hyponatremia, has very poor patient compliance over long term. Vasopressin receptor antagonists (Vaptans) are a new group of nonpeptide drugs which have been used in various clinical conditions with limited success. Whereas conivaptan is to be administered intravenously, the other vaptans like tolvaptan, lixivaptan, and satavaptan are effective as oral medication. They produce aquaresis by their action on vasopressin type 2 (V2R) receptors in the collecting duct and thus increase solute free water excretion. Vaptans are being used as an alternative to fluid restriction in euvolemic and hypervolemic hyponatremic patients. Efficacy of vaptans is now well accepted for management of correction of hyponatremia over a short period. However, its efficacy in improving the long-term morbidity and mortality in patients with chronic hyponatremia due to cirrhosis and heart failure is yet to be established. Vaptans have not become the mainstay treatment of hyponatremia yet.

Effect of loading dose and formulation on safety and efficacy of conivaptan in treatment of euvolemic and hypervolemic hyponatremia

PURPOSE

The effect of loading dose and formulation on the safety and efficacy of conivaptan in the treatment of euvolemic and hypervolemic hyponatremia was studied.

METHODS

This parallel-group study randomized 121 hospitalized patients with euvolemic or hypervolemic hyponatremia to one of four treatment regimens: placebo loading dose followed by conivaptan continuous i.v. infusion using the ampul formulation (regimen 1), conivaptan loading dose followed by continuous i.v. infusion using the ampul formulation (regimen 2), placebo loading dose followed by conivaptan continuous i.v. infusion using the premixed formulation (regimen 3), or conivaptan loading dose followed by continuous i.v. infusion using the premixed formulation (regimen 4). The primary variable was the incidence and severity of injection-site reactions (ISRs), as evaluated using the ISR modified 5-point scale (ISRMS). Secondary outcomes included effects on serum sodium concentration (SSC), duration of effect, and safety and tolerability.

RESULTS

All four dosing regimens were efficacious, safe, and well tolerated. No significant differences in ISRMS scores or differences in changes from baseline SSC or in the duration of effects on SSC were observed between the regimens. Overly rapid SSC increases occurred in 7%, 7%, 3%, and 21% of patients treated with regimens 1, 2, 3, and 4, respectively. Overall, adverse events related to general disorders and ISRs occurred in 39%, 43%, 53%, and 55% of patients receiving regimens 1, 2, 3, and 4, respectively.

CONCLUSION

Intravenous conivaptan regimens with or without a loading dose, whether using the ampul or a premixed formulation, had similar safety, tolerability, and efficacy in patients with euvolemic or hypervolemic hyponatremia. The pre-mixed formulation used with a loading dose may be associated with an increased frequency of overly rapid increase in SSC compared with the other regimens studied.

Vasopressin-receptor antagonists

Despite a crucial role in body fluid homeostasis, elevated vasopressin levels can also be pathological in conditions such as congestive heart failure, liver cirrhosis and the syndrome of inappropriate antidiuretic hormone secretion. The result of elevated vasopressin is renal water retention and hyponatremia, a low serum sodium concentration. Hyponatremia is associated with excess morbidity and mortality. Nonpeptide vasopressin-receptor antagonists represent a new drug class of small molecules that competitively inhibit one or more of the vasopressin receptors. There are three vasopressin receptors in humans, including V1a, V1b and V2. Selective V2- and combined V1a/V2-receptor antagonists have been developed for the treatment of hyponatremia resulting from congestive heart failure, liver cirrhosis and the syndrome of inappropriate antidiuretic hormone secretion. Two nonpeptide vasopressin-receptor antagonists, conivaptan and tolvaptan, have recently been approved by American and European drug authorities for clinical use. This article aims to provide a succinct and clinical update on nonpeptide vasopressin-receptor antagonists, including their mechanism of action, performance in randomized clinical trials and current clinical status.

Treatment of euvolemic hyponatremia in the intensive care unit by urea

INTRODUCTION

Hyponatremia in the intensive care unit (ICU) is most commonly related to inappropriate secretion of antidiuretic hormone (SIADH). Fluid restriction is difficult to apply in these patients. We wanted to report the treatment of hyponatremia with urea in these patients.

METHODS

Two groups of patients are reported. The first one is represented by a retrospective study of 50 consecutive patients with mild hyponatremia treated with urea. The second group is presented by a series of 35 consecutive patients with severe hyponatremia acquired outside the hospital (≤ 115 mEq/L) who where treated by isotonic saline and urea (0.5 to 1 g/kg/day), administered usually by gastric tube.

RESULTS

In the first group with mild hyponatremia (128 ± 4 mEq/L) the serum sodium (SNa) increased to a mean value of 135 ± 4 mEq/L (P < 0.001) after two days of urea therapy (46 ± 25 g/day), despite a large fluid intake (> 2 L/day). The mean duration of urea therapy was six days (from 2 to 42 days). Six patients developed hyponatremia again once the urea was stopped, which necessitated its reintroduction. Six patients developed hypernatremia (maximum value 155 mEq/L). In the second group, SNa increased from 111 ± 3 mEq/L to 122 ± 4 mEq/L in one day (P < 0.001). All the patients with neurological symptoms made a rapid recovery. No side effects were observed.

CONCLUSIONS

These data show that urea is a simple and inexpensive therapy to treat euvolemic hyponatremia in the ICU.

New horizons in the pharmacologic approach to hyponatremia: the V2 receptor antagonists

This article provides an overview of the developing niche for vasopressin 2 receptor antagonists ("vaptans") in the management of hyponatremia in clinical practice. Specific areas of focus include the physiological and clinical rationale for use of this class of medications (including advantages over older and less specific therapeutic modalities), the practical limitations to the use of these new drugs (including issues of tolerability, toxicity, risk, and cost), and the unanswered question of the extent to which correcting hyponatremia will improve clinical outcomes.

Efficacy and safety of oral conivaptan, a vasopressin-receptor antagonist, evaluated in a randomized, controlled trial in patients with euvolemic or hypervolemic hyponatremia

BACKGROUND

In most cases of hyponatremia, arginine vasopressin secretion is inappropriately high. This placebo-controlled, randomized, double-blind multicenter study evaluated the efficacy and safety of oral conivaptan, a V1A/V2-receptor antagonist, in patients with euvolemic or hypervolemic hyponatremia.

METHODS

Eighty-three patients with serum [Na] less than 130 mEq/L were stratified by volume status and randomly assigned to placebo or conivaptan 40 or 80 mg/d for 5 days.

RESULTS

Conivaptan increased the baseline-adjusted area under the serum [Na]-time curve significantly more than placebo (P = 0.0001). Patients given either dose of conivaptan demonstrated a serum [Na] of 4 mEq/L or greater above baseline significantly faster than those given placebo (P < 0.001) and maintained that increase for a greater total time (P = 0.0001). The least squares mean change in serum [Na] from baseline to end of treatment was also significantly greater with conivaptan 40 and 80 mg/d (6.8 and 8.8 mEq/L, respectively) (P = 0.0001) than that with placebo (1.2 mEq/L). The percentage of patients who obtained an increase from baseline in serum [Na] of 6 mEq/L or greater or normal serum [Na] was significantly higher among patients given conivaptan 40 and 80 mg/d (67% and 88%, respectively) than among those given placebo (20%; P < 0.001). Conivaptan was well tolerated; the most frequent adverse events were urinary tract infection, anemia, pyrexia, cardiac failure, hypotension, and hypokalemia.

CONCLUSION

Oral conivaptan was effective in increasing serum [Na] in patients with euvolemic or hypervolemic hyponatremia and had a favorable safety profile.

Pharmacology of vasopressin antagonists

Congestive heart failure (CHF) is characterized by fluid and water retention, which frequently is a therapeutic challenge. Most conventional diuretics act primarily as saluretics, i.e. they inhibit renal tubular electrolyte reabsorption, which due to osmotic pressure promotes excretion of isotonic fluid. Arginine vasopressin (AVP) via the V(1A) receptor vasoconstricts and via the V(2) receptor promotes water reabsorption in the renal collecting duct by inserting aquaporin-2 water channels into the luminal membrane. Novel V(2) receptor antagonists act as powerful aquaretics, i.e. they excrete free water. We review the pharmacology of non-selective V(1A)/V(2) receptor antagonists and selective V(2) receptor antagonists currently in clinical development.

Non-peptide arginine-vasopressin antagonists: the vaptans

Arginine-vasopressin is a hormone that plays an important part in circulatory and water homoeostasis. The three arginine-vasopressin-receptor subtypes--V1a, V1b, and V2--all belong to the large rhodopsin-like G-protein-coupled receptor family. The vaptans are orally and intravenously active non-peptide vasopressin receptor antagonists that are in development. Relcovaptan is a selective V1a-receptor antagonist, which has shown initial positive results in the treatment of Raynaud's disease, dysmenorrhoea, and tocolysis. SSR-149415 is a selective V1b-receptor antagonist, which could have beneficial effects in the treatment of psychiatric disorders. V2-receptor antagonists--mozavaptan, lixivaptan, satavaptan, and tolvaptan--induce a highly hypotonic diuresis without substantially affecting the excretion of electrolytes (by contrast with the effects of diuretics). These drugs are all effective in the treatment of euvolaemic and hypervolaemic hyponatraemia. Conivaptan is a V1a/V2 non-selective vasopressin-receptor antagonist that has been approved by the US Food and Drug Administration as an intravenous infusion for the inhospital treatment of euvolaemic or hypervolaemic hyponatraemia.