Multicenter, Randomized, Double-blind, Placebo-controlled Study to Evaluate the Efficacy and Safety of Oral Lixivaptan Capsules in Subject With Euvolemic Hyponatremia

Inclusion Criteria: * Written informed consent * Men or women aged 18 or older * Diagnosis of euvolemic hyponatremia (120 ≤ Na+\<130 mEq/L) * Hospitalized or willing to be admitted to a monitored setting for approximately the first 48 hours of treatment Exclusion Criteria: * Pregnant or breast-feeding women, or women planning to become pregnant or to breastfeed * Symptomatic hyponatremia (e.g., lethargy, coma, seizures, changes in mental status attributable to hyponatremia) * Acute or transient hyponatremia (e.g., associated with head trauma or postoperative state) * Hyponatremia in hypovolemic states. Hypovolemic hyponatremia is defined as the presence of clinical evidence of extracellular fluid volume depletion * Hyponatremia as a result of any medication that can safely be withdrawn * Hyponatremia due to hypothyroidism or adrenal insufficiency * Diagnosis of psychogenic polydipsia * Receiving within 7 days of enrollment, other medication for treatment of hyponatremia specifically: demeclocycline, lithium carbonate, urea, or conivaptan * Use of radiotherapy and chemotherapy within 2 wks of randomization * Likely to require, or to receive IV saline for correction of symptomatic or asymptomatic severe hyponatremia during the course of the study * Supine systolic arterial blood pressure of ≤ 90 mmHg * Serum creatinine \>3.0 mg/dL * History of uncontrolled type 2 diabetes mellitus * Severe pulmonary artery hypertension: patients whose condition is expected to deteriorate with sudden shifts in fluid volumes and cardiac filling pressures * Established diagnosis of New York Heart Association (NYHA) class III or IV heart failure * History of myocardial infarction, unstable angina or evidence of active ischemia within 30 days prior to screening * History of cerebral vascular accident (CVA) within 60 days prior to screening * Established diagnosis of nephrotic syndrome * Advanced liver disease or documented diagnosis of cirrhosis or alcoholic hepatitis * Urinary tract obstruction (benign prostatic hypertrophy \[BPH\] allowed if non-obstructive) * History of alcohol abuse or illicit drug use within the past 6 months * Terminally ill or moribund condition with little chance of short-term survival * Receiving vasopressin or its analogs for treatment of any condition * Known allergy to any vasopressin antagonist * Previous participation in a lixivaptan study * Recipient of any investigational treatment (drug or device) within 30 days prior to baseline visit * Unable to take oral medications