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Vaprisol

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Vaprisol

Vaprisol

CLINICAL PHARMACOLOGY

Mechanism of Action

Conivaptan hydrochloride is a dual arginine vasopressin (AVP) antagonist with nanomolar affinity for human V1A and V2 receptors in vitro. The level of AVP in circulating blood is critical for the regulation of water and electrolyte balance and is usually elevated in both euvolemic and hypervolemic hyponatremia. The AVP effect is mediated through V2 receptors, which are functionally coupled to aquaporin channels in the apical membrane of the collecting ducts of the kidney. These receptors help to maintain plasma osmolality within the normal range. The predominant pharmacodynamic effect of conivaptan hydrochloride in the treatment of hyponatremia is through its V2 antagonism of AVP in the renal collecting ducts, an effect that results in aquaresis, or excretion of free water.

Pharmacodynamics

The pharmacodynamic effects of conivaptan hydrochloride include increased free water excretion (i.e., effective water clearance [EWC]) generally accompanied by increased net fluid loss, increased urine output, and decreased urine osmolality. Studies in animal models of hyponatremia showed that conivaptan hydrochloride prevented the occurrence of hyponatremia-related physical signs in rats with the syndrome of inappropriate antidiuretic hormone secretion.

Electrophysiology

The effect of VAPRISOL 40 mg IV and 80 mg IV on the QT interval was evaluated after the first dose (Day 1) and at the last day during treatment (Day 4) in a randomized, single-blind, parallel group, placebo- and positive-controlled (moxifloxacin 400 mg IV) study in healthy male and female volunteers aged 18 to 45 years. Digital ECGs were obtained at baseline and on Days 1 and 4. Moxifloxacin elicited placebo-corrected changes from baseline in individualized QT correction (QTcI) of +7 to +10 msec on Days 1 and 4, respectively, indicating that the study had assay sensitivity. The placebo-corrected changes from baseline in QTcI in the VAPRISOL 40 mg and 80 mg dose groups on Day 1 were -3.5 msec and -2.9 msec, respectively, and -2.1 msec for both dose groups on Day 4. The results suggest that conivaptan has no clinically significant effect on cardiac repolarization.

Pharmacokinetics

The pharmacokinetics of conivaptan have been characterized in healthy subjects, special populations and patients following both oral and intravenous dosing regimens. The pharmacokinetics of conivaptan following intravenous infusion (40 mg/day to 80 mg/day) and oral administration are non-linear, and inhibition by conivaptan of its own metabolism seems to be the major factor for the non-linearity. The intersubject variability of conivaptan pharmacokinetics is high (94% CV in CL).

The pharmacokinetics of conivaptan and its metabolites were characterized in healthy male subjects administered conivaptan hydrochloride as a 20 mg loading dose (infused over 30 minutes) followed by a continuous infusion of 40 mg/day for 3 days. Mean Cmax for conivaptan was 619 ng/mL and occurred at the end of the loading dose. Plasma concentrations reached a minimum at approximately 12 hours after start of the loading dose, then gradually increased over the duration of the infusion to a mean concentration of 188 ng/mL at the end of the infusion. The mean terminal elimination half-life after conivaptan infusion was 5.0 hours, and the mean clearance was 253.3 mL/min.

In an open-label safety and efficacy study, the pharmacokinetics of conivaptan were characterized in hypervolemic or euvolemic hyponatremia patients (ages 20 - 92 years) receiving conivaptan hydrochloride as a 20 mg loading dose (infused over 30 minutes) followed by a continuous infusion of 20 or 40 mg/day for 4 days. The median-plasma conivaptan concentrations are shown in Figure 1. The median (range) elimination half-life was 5.3 (3.3 - 9.3) or 8.1 (4.1 - 22.5) hours in the 20 mg/day or 40 mg/day group, respectively, based on data from rich PK sampling.

Figure 1: Median Plasma Concentration-Time Profiles From Rich PK Sampling After 20 mg Loading Dose and 20 mg/day (open circle) or 40 mg/day (closed circle) Infusion for 4 Days

Median Plasma Concentration-Time Profiles - Illustration

Distribution

Conivaptan is extensively bound to human plasma proteins, being 99% bound over the concentration range of approximately 10 to 1000 ng/mL.

Metabolism and Excretion

CYP3A was identified as the sole cytochrome P450 isozyme responsible for the metabolism of conivaptan. Four metabolites have been identified. The pharmacological activity of the metabolites at V1A and V2 receptors ranged from approximately 3-50% and 50-100% that of conivaptan, respectively. The combined exposure of the metabolites following intravenous administration of conivaptan is approximately 7% that of conivaptan and hence, their contribution to the clinical effect of conivaptan is minimal.

After intravenous (10 mg) or oral (20 mg) administration of conivaptan hydrochloride in a mass balance study, approximately 83% of the dose was excreted in feces as total radioactivity and 12% in urine over several days of collection. Over the first 24 hours after dosing, approximately 1% of the intravenous dose was excreted in urine as intact conivaptan.

Special Populations

Hepatic Impairment

The systemic exposure to conivaptan is approximately doubled in subjects with moderate hepatic impairment. No clinically relevant increase in exposure was observed in subjects with mild hepatic impairment. The impact of severe hepatic impairment on the exposure to conivaptan has not been studied [see DOSAGE AND ADMINISTRATION and Use In Specific Populations].

Renal Impairment

Mild and moderate renal impairment (CLcr 30 – 80 mL/min) do not affect exposure to VAPRISOL to a clinically relevant extent. Use in patients with severe renal impairment (CLcr < 30 mL/min) is not recommended [see Use In Specific Populations].

Clinical Studies

Hyponatremia

The effect on serum sodium of VAPRISOL was demonstrated in a double-blind, placebo-controlled, randomized, multicenter study conducted in 84 patients with euvolemic (N=56) or hypervolemic (N=28) hyponatremia (serum sodium 115 -130 mEq/L) from a variety of underlying causes (malignant or nonmalignant diseases of the central nervous system, lung, or abdomen; congestive heart failure; hypertension; myocardial infarction; diabetes; osteoarthritis; or idiopathic). Study participants were randomized to receive either placebo IV (N=29), VAPRISOL 40 mg/day IV (N=29), or VAPRISOL 80 mg/day IV (N=26). Daily fluid intake was restricted to 2 liters. VAPRISOL or placebo was administered as a continuous infusion following a 30 minute IV loading dose on the first treatment day and patients were treated for 4 days. Serum or plasma sodium concentrations were assessed pre-dose (Hour 0) and at 4, 6, 10, and 24 hours post-dose on all treatment days.

Mean serum sodium concentration was 123.3 mEq/L at study entry. The mean change in serum sodium concentration from baseline over the 4-day treatment period is shown in Figure 2.

Figure 2: Mean (SE) Change from Baseline in Sodium Concentrations with VAPRISOL 40 mg/day

Mean (SE) Change from Baseline in Sodium Concentrations with VAPRISOL 40 mg/day - Illustration

Following treatment with 40 mg/day of VAPRISOL, the mean change from baseline in serum sodium concentration at the end of 2 days of treatment with VAPRISOL was 5.3 mEq/L (mean concentration 128.6 mEq/L). At the end of the 4-day treatment period, the mean change from baseline was 6.5 mEq/L (mean concentration 129.8 mEq/L). In addition, after 2 days and 4 days of treatment with VAPRISOL, 41% (after 2 days) and 69% (after 4 days) of patients achieved a ≥ 6 mEq/L increase in serum sodium concentration or a normal serum sodium of ≥ 135 mEq/L. Although 80 mg/day was also studied, it was not significantly more effective than 40 mg/day and was associated with a higher incidence of infusion site reactions and a higher rate of discontinuations for adverse events [see ADVERSE REACTIONS]. Additional efficacy data are summarized in Table 2.

Table 2: Efficacy Outcomes of Treatment with VAPRISOL 40 mg/day

Efficacy Variable Placebo
N=29
VAPRISOL 40 mg/day
N=29
Day 2‡ Day 4 Day 2‡ Day 4
Baseline adjusted serum Na+ AUC over duration of treatment (mEq•hr/L)
Mean (SD) 6.2 (81.8) 61.4 (242.3) 205.9 (171.6) 500.8 (365.5)
LS Mean ± SE 3.8 ± 26.9 12.9 ± 61.2 205.6 ± 26.6 * 490.9 ± 56.8 *
Number of patients (%) and median event time (h) from first dose of study medication to a confirmed ≥ 4 mEq/L increase from Baseline in serum Na+, [95% CI] 2 (7%) 9 (31%) 22 (76%) 23 (79%)
Not estimable Not estimable 23.7 * 23.7 *
Not estimable Not estimable [10, 2] [10, 2]
Serum Na+ (mEq/L)
  Baseline mean (SD) 124.3 (4.1) 124.3 (4.1) 123.3 (4.7) 123.3 (4.7)
  Mean (SD) at end of treatment 124.5 (4.7) 125.8 (4.9) 128.6 (5.9) 129.8 (4.8)
  Change from Baseline to end of treatment
     Mean change (SD) 0.2 (2.5) 1.5 (4.6) 5.3 (4.4) 6.5 (4.4)
     LS Mean change ± SE 0.1 ± 0.7 0.8 ± 0.8 5.2 ± 0.7* 6.3 ± 0.7*
Number (%) of patients who obtained a confirmed ≥ 6 mEq/L increase from Baseline in serum Na+ or a normal serum Na+ concentration ≥ 135 mEq/L during treatment 0 (0) 6 (21%) 12 (41%)* 20 (69%)*
*: P ≤ 0.001 vs placebo
‡: efficacy variables were assessed on Day 2 of a 4-day treatment period

The aquaretic effect of VAPRISOL is shown in Figure 3. VAPRISOL produced a baseline-corrected cumulative increase in effective water clearance of over 3800 mL compared to approximately 1300 mL with placebo by Day 4.

Figure 3: Baseline-Corrected Mean (SE) Cumulative Effective Water Clearance (EWC)

Baseline-Corrected Mean (SE) Cumulative Effective Water Clearance - Illustration

EWC = V x (1-UNa + Uκ/PNa+Pκ), where V is urine volume (mL/d), UNa is urine sodium concentration, UK is urine potassium concentration, PNa is plasma/serum sodium concentration, and PK is plasma/serum potassium concentration.

The effect on serum sodium of VAPRISOL (administered as a 20 or 40 mg/day IV continuous infusion for 4 days following a 30 minute IV infusion of a 20 mg loading dose on the first treatment day) was also evaluated in an open-label study of 251 patients with euvolemic or hypervolemic hyponatremia. The results are shown in Table 3.

Table 3: Efficacy Outcomes of Treatment with VAPRISOL 20 or 40 mg/day

Primary Efficacy Endpoint 20 mg/day
N=37
40 mg/day
N=214
Baseline adjusted serum Na+ AUC over duration of treatment
(mEq•hr/L) Mean (SD) 753.8 (429.9) 689.2 (417.3)
Secondary Efficacy Endpoints
Number of patients (%) 29 (78%) 178 (83%)
and median event time (h) from first dose of study medication to a confirmed ≥ 4 mEq/L increase from Baseline in serum Na+, [95% CI] 23.8[12.0, 36.0] 24.4 [24.0, 35.8]
Total time (h) from first dose of study medication to end of treatment during which patients had a confirmed ≥ 4 mEq/L increase in serum Na+ from Baseline Mean (SD) 60.6 (35.2) 59.5 (33.2)
Serum Na+ (mEq/L)
  Baseline mean (SD) 122.5 (5.2) 123.8 (4.6)
  Mean (SD) at end of treatment 131.8 (3.9) 132.5 (4.6)
  Mean Change (SD) from Baseline to End of Treatment 9.4 (5.3) 8.8 (5.4)
  Mean (SD) at Follow-up Day 11 129.9 (6.2) 131.8 (5.8)
  Mean Change (SD) from Baseline to Follow-up Day 11 7.1 (8.2) 8.0 (6.5)
  Mean (SD) at Follow-up Day 34 134.3 (4.5) 134.3 (5.2)
  Mean Change (SD) from Baseline to Follow-up Day 34 11.5 (7.3) 10.7 (6.7)
Number (%) of patients who obtained a confirmed ≥ 6 mEq/L increase from Baseline in serum Na+ or a normal serum Na+ concentration ≥ 135 mEq/L during treatment 26 (70%) 154 (72%)

Heart Failure

The effectiveness of VAPRISOL for the treatment of congestive heart failure has not been established. In ten Phase 2/pilot heart failure studies, VAPRISOL did not show statistically significant improvement for heart failure outcomes, including such measures as length of hospital stay, changes in categorized physical findings of heart failure, change in ejection fraction, change in exercise tolerance, change in functional status, or change in heart failure symptoms, compared to placebo. In these studies, the changes in the physical findings and heart failure symptoms were no worse in the VAPRISOL-treated group (N=818) compared to the placebo group (N=290) [see INDICATIONS AND USAGE].

Last reviewed on RxList: 2/28/2012
This monograph has been modified to include the generic and brand name in many instances.

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