Therapeutic effect of conivaptan bolus dosing in hyponatremic neurosurgical patients

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 48 hours was determined. The primary end point was an increase in serum sodium level of 4 mEq/L or greater over the first 24 hours. The mean ± SD baseline serum sodium level was 129.8 ± 3.4 mEq/L, which increased to 133.1 ± 3.2 mEq/L at 6 hours after administration of the bolus dose of conivaptan. The serum sodium level at 24 hours was 134.2 ± 3.2 mEq/L, indicating a 24-hour natremic response of 4.3 ± 2.6 mEq/L (range 1-13 mEq/L) from baseline (p<0.001). Eighteen patients (56%) met the primary end point. The mean ± SD fluid balance over the first 24 hours was -783 ± 440 ml. The mean ± SD change in serum sodium level from 24 to 48 hours was 0.5 ± 1.3 mEq/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.