The potential role for lixivaptan in heart failure and in hyponatremia

Evaluation of lixivaptan in euvolemic and hypervolemic hyponatremia and heart failure treatment

INTRODUCTION

Lixivaptan is a selective vasopressin type 2 (V2) receptor antagonist that induces aquaresis, the electrolytes sparing excretion of water. Its ability to correct hyponatremia has been demonstrated in experimental animal studies as well as in clinical trials in humans. Recently, three Phase III, double-blind, randomized, placebo-controlled studies have been completed. In two studies, patients with euvolemic hyponatremia were enrolled, one in the inpatient and the other in the outpatient setting and the third study involved patients with hypervolemic hyponatremia hospitalized for decompensated heart failure (HF). The trials confirmed the efficacy of lixivaptan in raising serum sodium but raised concern about its safety in patients hospitalized with decompensated HF.

AREAS COVERED

The authors review original publications on lixivaptan and summarize their findings. Specifically, the authors present information regarding its structure, pharmacodynamics and kinetics, metabolism as well as its efficacy and safety in laboratory animals and human studies. Furthermore, the FDA website was accessed to obtain information presented at the September 13, 2012 meeting of the Cardiovascular and Renal Drugs Advisory Committee.

EXPERT OPINION

The published data indicate that lixivaptan raises sodium levels in hyponatremic patients and supports its use in patients with euvolemic hyponatremia. However, the authors note that more safety data are still needed specifically in patients with decompensated HF.

Assessment of exposure of metabolites in preclinical species and humans at steady state from the single-dose radiolabeled absorption, distribution, metabolism, and excretion studies: a case study

The exposure of a drug candidate and its metabolites in humans and preclinical species during drug development needs to be determined to ensure that the safety of drug-related components in humans is adequately assessed in the standard toxicology studies. The in vivo radiolabeled studies in preclinical species and human volunteers provide the total fate of the drug-derived radioactivity including the relative abundance of metabolites. Here, we describe how the single-dose radiolabeled human studies could provide the exposure of circulating metabolites at steady state using a case study of an extensively metabolized drug, lixivaptan. After an oral dose of [(14)C]lixivaptan to humans, a total of nine metabolites were detected in the systemic circulation; eight of them exceeded 10% of the parent exposure (2-41% of total radioactivity). The plasma samples were profiled for all subjects at each time point by high-performance liquid chromatography, and metabolites were quantified using a radioactive detector. On the basis of single-dose area under the concentration-time curve (AUC) values, exposure of six human metabolites was greater at least in one preclinical species used in toxicology evaluation. On the basis of the t(1/2) of lixivaptan and two major metabolites from a single dose in humans, their AUC and C(max) values were simulated at the steady state. The simulated exposure (C(max) and AUC) values of parent drug and the two most abundant metabolites were similar to those from a 7-day clinical study obtained using a validated liquid chromatography-mass spectrometry assay, suggesting that a well designed single-dose radiolabeled human study can help in addressing the metabolites in safety testing-related issues.