Hyponatremia Clinical Update, July 29, 2011

The latest in research on hyponatremia.

Intravenous Conivaptan in Neurosurgical Patients with Hyponatremia from Syndrome of Inappropriate Antidiuretic Hormone Secretion

According to recently published data, conivaptan can be safely used for the treatment of hyponatremia induced by syndrome of inappropriate antidiuretic hormone secretion (SIADH) in the neurosurgical arena.

According to the study, which was published in Neurosurgery, SIADH is the most common cause of hyponatremia in hospitalized patients and is frequently associated with neurologic disorders and neurosurgical procedures.

“Traditional therapies such as fluid restriction, sodium repletion, and diuretics can help correct hyponatremia but do not address the underlying pathophysiology of excess arginine vasopressin secretion,” wrote the authors, who were headed by Matthew Potts, MD, in the department of neurological surgery at the University of California, San Francisco.

“Conivaptan is an arginine vasopressin receptor antagonist that has been shown to be both safe and effective in the treatment of euvolemic and hypervolemic hyponatremia.”

The researchers conducted a retrospective review of 13 patients with neurosurgical disorders with SIADH that were treated with intravenous conivaptan at their institution between 2007 and 2009.

“The mean pretreatment serum sodium concentration was 125.8 ± 3.5 mEq/L. Conivaptan administration resulted in a rise in serum sodium to 132.5 ± 5.6 mEq/L at 12 hours (P<.01) and 134.1 ± 4.7 mEq/L at 24 hours posttreatment (P<.01). The mean time to an increase in serum sodium ≥ 6 mEq/L was 17.8 hours,” the authors wrote.

There were no instances of rapid overcorrection. There were three cases of asymptomatic hyperkalemia, three cases of asymptomatic hypotension, and one case of elevated creatinine associated with conivaptan administration.

Influence of Aquaporin-1 Gene Polymorphism on Water Retention in Liver Cirrhosis

The results of a recent study suggest that a polymorphism could be involved in the genetic susceptibility to develop water retention in patients with liver cirrhosis.

Water retention is a major clinical problem in patients with liver cirrhosis. The factors that predispose to water retention are poorly understood but may involve genetic factors, according to a study published in the Scandinavian Journal of Gastroenterology by researchers at the University Hospital Marqués de Valdecilla in Santander, Spain.

“Recent research suggests that renal aquaporins may be a pathophysiological factor involved in this condition. Aquaporin-1 (AQP1) is expressed in the proximal tubule and aquaporin-2 (AQP2) in the renal collecting duct cells. The aim of our study was to investigate the distribution of single nucleotide polymorphisms (SNPs) of AQP1: rs1049305 (C/G) and AQP2: rs3741559 (A/G) and rs467323 (C/T) in 100 cirrhotic patients with ascites and to analyze their relationship with dilutional hyponatremia,” the authors wrote in the study abstract.

Genomic DNA was extracted from peripheral blood. Genotyping for the presence of different polymorphisms was performed using the Custom Taqman SNP Genotyping Assays. The possible influence of rs1049305 (C/G) in AQP1 gene expression was evaluated by luciferase assays in vitro.

“The allelic frequencies of the AQP1 gene were the following: CC = 15%; CG = 49%; GG = 36%,” the authors wrote. “Patients with CC genotype had significantly lower plasma sodium concentration than those with CG or GG genotype. Luciferase assays showed that the rs1049305 (C/G) in the AQP1 gene functionally affected the expression level in vitro. In addition, we did not find any relationship between AQP2 SNPs observed and plasma sodium concentration.”

Sources

Use of intravenous conivaptan in neurosurgical patients with hyponatremia from syndrome of inappropriate antidiuretic hormone secretion [Neurosurgery]

Influence of aquaporin-1 gene polymorphism on water retention in liver cirrhosis [Scandinavian Journal of Gastroenterology]