Vaprisol Is Effective, Safe In Promptly Increasing Serum Sodium Levels

Armen Hareyan's picture
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Astellas Pharma announced results of an analysis showing that Vaprisol (conivaptan hydrochloride injection) produced a prompt and sustained (over the 4-day treatment period) increase in serum sodium concentration [Na+] among hospitalized patients with euvolemic and hypervolemic hyponatremia with a low risk of overly rapid [Na+] correction. The study results were presented during the annual meeting of the American College of Emergency Physicians in Seattle.

"Acute hyponatremia is a serious condition that requires immediate medical attention," said Lynne E. Wagoner, MD, Director of Heart Failure, Greater Cincinnati Cardiovascular Consultants. "These data demonstrated that Vaprisol promptly and safely increased [Na+] in patients with euvolemic and hypervolemic hyponatremia."

Vaprisol is the first in a new class of arginine vasopressin (AVP) receptor antagonists. Vaprisol blocks both V1a and V2 vasopressin receptors, resulting in increased urine output without increased sodium loss. This effect, known as "aquaresis," increases serum sodium levels and helps to restore salt and water balance in patients with hyponatremia due to increased body water (dilutional hyponatremia).

Vaprisol is approved by the U.S. Food and Drug Administration as a treatment for euvolemic and hypervolemic hyponatremia in hospitalized patients. Vaprisol is not indicated for the treatment of congestive heart failure. It should only be used for the treatment of hyponatremia in patients with underlying heart failure when the expected benefit of raising serum sodium outweighs the increased risk of adverse events. The approved treatment regimen for Vaprisol starts with a 20 mg loading dose followed by a continuous infusion of 20 mg/day, which may be titrated to 40 mg/day if necessary. The 80 mg/day dose included in this analysis is not an approved dose.

Study Findings

The post-hoc pooled analysis is based on results from a randomized controlled trial (RCT) of 84 patients and an open-label study (OLS) of 251 patients, all with euvolemic or hypervolemic hyponatremia.

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After infusion of a 20 mg loading dose or placebo, Vaprisol was given in a continuous 4-day infusion of 40 or 80 mg/d in the RCT and 20 or 40 mg/d in the OLS. The pooled analysis evaluated the frequency of overly rapid [Na+] increases during Vaprisol clinical trials. Note: Overly rapid [Na+] increase can lead to serious neurologic sequelae associated osmotic demyelinization syndrome. This study defined overly rapid increase of serum [Na+] as an increase in serum [Na+] > 12 mEq/L in 24 hours.

In both studies, baseline characteristics were largely similar between those who had an overly rapid increase in [Na+] and those who did not. Among patients who received Vaprisol in the RCT, the mean change in [Na+] was significantly higher compared to the placebo group throughout the 4-day course of treatment. In the OLS, both doses of Vaprisol produced prompt increases that were sustained throughout the 4-day study. The median time to a confirmed greater than or equal to 4 mEq/L increase in [Na+] was approximately 24 hours in all Vaprisol groups in both studies.

Overall, these two clinical studies demonstrated an overly rapid [Na+] increase in about 5 percent of patients who received Vaprisol for the treatment of hyponatremia. In the RCT, 2 (7 percent) of the 29 patients treated with Vaprisol 40 mg/d, 2 (8 percent) of the 26 treated with Vaprisol 80 mg/d, and 0 of the 29 treated with placebo met the protocol-defined criteria for excessive or overly rapid increase of [Na+]. In the OLS, 1 (3 percent) of 37 patients treated with Vaprisol 20 mg/d and 10 (5 percent) of 214 treated with 40 mg/d met the protocol-defined criteria for excessive or overly rapid increase of [Na+].

None of these patients in either the RCT or the OLS experienced adverse events (AEs) associated with the overly rapid increases in [Na+]. Also, no cases of osmotic demyelination syndrome were reported from patients who experienced an overly rapid increase in [Na+] in either study.

About Hyponatremia

Hyponatremia often results from elevated levels of the hormone arginine vasopressin (AVP), which regulates water and salt balance in the body. It is the most common electrolyte disorder in clinical medicine.

Syndrome of inappropriate antidiuretic hormone (SIADH), advanced kidney failure, hypothyroidism, cancer and chronic high blood pressure are common causes of hyponatremia. Dilutional hyponatremia, which includes euvolemic and hypervolemic hyponatremia, is the most common form of the condition, and occurs when retained water dilutes serum sodium content. Patients with hyponatremia are classified as hypervolemic if swelling of body tissues (edema) is present or euvolemic if there is an increase in total body water content without edema.

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