Therapeutic Effect of Conivaptan Bolus Dosing in Hyponatremic Neurosurgical Patients

Abstract

To determine the natremic response of a single 20-mg bolus dose of conivaptan, an arginine vasopressin antagonist, in hyponatremic neurosurgical patients with the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Retrospective medical record review. Neurosurgical intensive care unit of a tertiary care referral hospital. Thirty-two hyponatremic patients with SIADH who were admitted to the neurosurgical intensive care unit and received a single 20-mg bolus dose of conivaptan between January and December 2011. Each patient's natremic response over 48hours was determined. The primary end point was an increase in serum sodium level of 4mEq/L or greater over the first 24hours. The mean ± SD baseline serum sodium level was 129.8±3.4 mEq/L, which increased to 133.1±3.2mEq/L at 6hours after administration of the bolus dose of conivaptan. The serum sodium level at 24hours was 134.2±3.2mEq/L, indicating a 24-hour natremic response of 4.3±2.6mEq/L (range 1-13mEq/L) from baseline (p<0.001). Eighteen patients (56%) met the primary end point. The mean ± SD fluid balance over the first 24hours was -783±440 ml. The mean ± SD change in serum sodium level from 24 to 48hours was 0.5±1.3mEq/L. No adverse effects or injection-site reactions were noted. The patients who failed to reach the primary end point were treated with repeated doses of conivaptan plus other agents. We recommend a single 20-mg dose of conivaptan as the preferred initial approach to treating patients with SIADH who are in the neurosurgical intensive care unit. The 24-hour natremic response should then dictate whether additional doses of conivaptan or other therapeutic interventions are required. We believe that such an approach is safe and will result in a controlled and predictable increase in the serum sodium concentration.