• Zhongping Lily Mao, Dennis Stalker, and James Keirns.
• Impax Laboratories, Hayward, California, USA.
• Clin Ther. 2009 Jul 1;31(7):1542-50.

BackgroundConivaptan is a nonpeptide vasopressin V(1A)/V(2)-receptor antagonist that produces a controlled increase in serum sodium concentration in hospitalized patients with euvolemic or hyper-volemic hyponatremia.ObjectiveThis study evaluated the pharmacokinetics of conivaptan in patients with euvolemic or hypervolemic hyponatremia and with or without underlying congestive heart failure who were participating in an efficacy and tolerability clinical trial.MethodsData from an open-label, multicenter study were used to evaluate the pharmacokinetics of conivaptan in hyponatremic patients. Patients received a 20-mg loading dose intravenously over 30 minutes, followed by a continuous 4-day infusion of 20 or 40 mg/d. In the entire cohort, plasma conivaptan concentrations were determined at baseline, at the end of the loading dose (0.5 hour), at 24 hours, on days 3 and 4, and at the follow-up visit on day 11. A subset of patients at 2 study sites (the "pharmacokineticrich" subset) provided additional samples for pharmacokinetic analysis on day 1 at 1, 4, and 24 hours; on day 2 at 24 hours; and on day 5 at 1, 2, 7, 12, and 24 hours.ResultsPlasma conivaptan concentrations were evaluated in 31 patients who received conivaptan 20 mg/d (mean [SD] age, 73.1 [14.3] years; weight, 68.1 [17.2] kg; 71.0% female; 87.1% white, 9.7% black, 3.2% other) and 172 patients who received co-nivaptan 40 mg/d (mean [SD] age, 71.5 [14.4] years; weight, 65.6 [15.9] kg; 64.0% female; 90.1% white, 6.4% black, 3.5% other). The pharmacokinetic-rich subset included 8 patients who received conivap-tan 20 mg/d (mean [SD] age, 76.3 [12.4] years; weight, 71.5 [14.7] kg; 87.5% female; 100% white) and 8 who received conivaptan 40 mg/d (mean [SD] age, 78.3 [7.9] years; weight, 71.3 [15.6] kg; 37.5% female; 100% white). In the overall patient group, plasma conivaptan concentrations were the highest after the 30-minute (C(0.5h)) loading dose (mean [SD] C(0.5h) = 733 [323] and 701 [343] ng/mL with conivap-tan 20 and 40 mg/d, respectively) and then declined during day 1 to concentrations (C(24h)) (mean [SD] C(24h) = 84 [78] and 215 [129] ng/mL with conivaptan 20 and 40 mg/d, respectively) that were maintained by the continuous infusion of 20 or 40 mg/d. At the end of infusion (96 hours), the mean (SD) plasma conivaptan concentrations were 176 (196) and 308 (321) ng/mL for conivaptan 20 and 40 mg/d, respectively. A ratio of 1.75 indicated near dose proportionality; however, interpatient variability was evident. No apparent differences in plasma conivaptan concentrations measured at 0.5 or 96 hours were observed between patients with euvolemic or hypervolemic hypona-tremia or between patients with or without congestive heart failure. In the pharmacokinetic-rich subset, for conivaptan 20 and 40 mg/d, respectively, conivaptan clearance was 18.7 and 9.5 L/h, the elimination t1/2 was 5.3 and 10.2 hours, and exposure to conivaptan in terms of AUC(infinity) was 6996 and 30,771 ng . h/mL.ConclusionThe results of this study suggest that the pharmacokinetics of conivaptan 20 and 40 mg/d do not differ by volume status or the presence or absence of congestive heart failure.

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