Tolvaptan (Page 5 of 7)
13 NONCLINICAL TOXICOLOGY
13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility
The carcinogenic potential of tolvaptan was assessed in 2-year carcinogenicity studies in mice and rats. Tolvaptan did not increase tumors in male or female rats at doses up to 1000 mg/kg/day (1.24 to 3.26 times the exposure in CHF patients based on AUC at the MRHD of 60 mg), in male mice at doses up to 60 mg/kg/day (0.3 times the exposure in CHF patients at the MRHD) and to female mice at doses up to 100 mg/kg/day (0.4 times the exposure in CHF patients at the MRHD).
Tolvaptan was not clastogenic in the in vitro chromosomal aberration test in Chinese hamster lung fibroblast cells or the in vivo rat micronucleus assay and was not mutagenic in the in vitro bacterial reverse mutation assays.
Impairment of fertility
In a fertility study in which male and female rats were administered tolvaptan orally at 100, 300 or 1000 mg/kg/day, altered estrous cycles due to prolongation of diestrus were observed in dams given 300 and 1000 mg/kg/day (6.2 and 11 times the exposure in CHF patients at the 60 mg dose). Tolvaptan had no effect on copulation or fertility indices. There were also no effects on the incidences of early or late resorption, dead fetuses, pre- or post-implantation loss, external anomalies, or fetal body weights.
14 CLINICAL STUDIES
In two double-blind, placebo-controlled, multi-center studies (SALT-1 and SALT-2), a total of 424 patients with euvolemic or hypervolemic hyponatremia (serum sodium <135 mEq/L) resulting from a variety of underlying causes (heart failure, liver cirrhosis, syndrome of inappropriate antidiuretic hormone [SIADH] and others) were treated for 30 days with tolvaptan or placebo, then followed for an additional 7 days after withdrawal. Symptomatic patients, patients likely to require saline therapy during the course of therapy, patients with acute and transient hyponatremia associated with head trauma or postoperative state and patients with hyponatremia due to primary polydipsia, uncontrolled adrenal insufficiency or uncontrolled hypothyroidism were excluded. Patients were randomized to receive either placebo (N = 220) or tolvaptan (N = 223) at an initial oral dose of 15 mg once daily. The mean serum sodium concentration at study entry was 129 mEq/L. Fluid restriction was to be avoided if possible during the first 24 hours of therapy to avoid overly rapid correction of serum sodium, and during the first 24 hours of therapy 87% of patients had no fluid restriction. Thereafter, patients could resume or initiate fluid restriction (defined as daily fluid intake of ≤1.0 liter/day) as clinically indicated.
The dose of tolvaptan could be increased at 24-hour intervals to 30 mg once daily, then to 60 mg once daily, until either the maximum dose of 60 mg or normonatremia (serum sodium >135 mEq/L) was reached. Serum sodium concentrations were determined at 8 hours after study drug initiation and daily up to 72 hours, within which time titration was typically completed. Treatment was maintained for 30 days with additional serum sodium assessments on Days 11, 18, 25 and 30. On the day of study discontinuation, all patients resumed previous therapies for hyponatremia and were reevaluated 7 days later. The primary endpoint for these studies was the average daily AUC for change in serum sodium from baseline to Day 4 and baseline to Day 30 in patients with a serum sodium less than 135 mEq/L. Compared to placebo, tolvaptan caused a statistically greater increase in serum sodium ( p <0.0001) during both periods in both studies (see Table 2). For patients with a serum sodium of <130 mEq/L or <125 mEq/L, the effects at Day 4 and Day 30 remained significant (see Table 2). This effect was also seen across all disease etiology subsets (e.g., CHF, cirrhosis, SIADH/other). Table 2. Effects of Treatment with Tolvaptan 15 mg/day to 60 mg/day
|Tolvaptan 15 mg/day to 60 mg/day||Placebo||Estimated Effect (95% CI)|
|Subjects with Serum Sodium <135 mEq/L (ITT population)|
|Change in average daily serum [Na+] AUC baseline to Day 4 (mEq/L) Mean (SD) N||4.0 (2.8) 213||0.4 (2.4) 203||3.7 (3.3 to 4.2) p <0.0001|
|Change in average daily serum [Na+] AUC baseline to Day 30 (mEq/L) Mean (SD) N||6.2 (4.0) 213||1.8 (3.7) 203||4.6 (3.9 to 5.2) p <0.0001|
|Percent of Patients Needing Fluid Restriction*||14% 30/215||25% 51/206||p= 0.0017|
|Subgroup with Serum Sodium <130 mEq/L|
|Change in average daily serum [Na+] AUC baseline to Day 4 (mEq/L) Mean (SD) N||4.8 (3.0) 110||0.7 (2.5) 105||4.2 (3.5 to 5.0) p <0.0001|
|Change in average daily serum [Na+] AUC baseline to Day 30 (mEq/L) Mean (SD) N||7.9 (4.1) 110||2.6 (4.2) 105||5.5 (4.4 to 6.5) p <0.0001|
|Percent of Patients Needing Fluid Restriction*||19% 21/110||36% 38/106||p <0.01|
|Subgroup with Serum Sodium <125 mEq/L|
|Change in average daily serum [Na+] AUC baseline to Day 4 (mEq/L) Mean (SD) N||5.7 (3.8) 26||1.0 (1.8) 30||5.3 (3.8 to 6.9) p <0.0001|
|Change in average daily serum [Na+] AUC baseline to Day 30 (mEq/L) Mean (SD) N||10.0 (4.8) 26||4.1 (4.5) 30||5.7 (3.1 to 8.3) p <0.0001|
|Percent of Patients Needing Fluid Restriction*||35% 9/26||50% 15/30||p = 0.14|
* Fluid Restriction defined as <1L/day at any time during treatment period.
In patients with hyponatremia (defined as <135 mEq/L), serum sodium concentration increased to a significantly greater degree in tolvaptan-treated patients compared to placebo-treated patients as early as 8 hours after the first dose, and the change was maintained for 30 days. The percentage of patients requiring fluid restriction (defined as ≤1 L/day at any time during the treatment period) was also significantly less (
in the tolvaptan-treated group (30/215, 14%) as compared with the placebo-treated group (51/206, 25%).
Figure 1 shows the change from baseline in serum sodium by visit in patients with serum sodium <135 mEq/L. Within 7 days of tolvaptan discontinuation, serum sodium concentrations in tolvaptan-treated patients declined to levels similar to those of placebo-treated patients. Figure 1: Pooled SALT Studies: Analysis of Mean Serum Sodium (± SD, mEq/L) by Visit — Patients with Baseline Serum Sodium <135 mEq/L
*p-value <0.0001 for all visits during tolvaptan treatment compared to placebo Figure 2: Pooled SALT Studies: Analysis of Mean Serum Sodium (± SD, mEq/L) by Visit — Patients with Baseline Serum Sodium <130 mEq/L
*p-value <0.0001 for all visits during tolvaptan treatment compared to placebo
In the open-label study SALTWATER, 111 patients, 94 of them hyponatremic (serum sodium <135 mEq/L), previously on tolvaptan or placebo therapy, were given tolvaptan as a titrated regimen (15 to 60 mg once daily) after having returned to standard care for at least 7 days. By this time, their baseline mean serum sodium concentration had fallen to between their original baseline and post-placebo therapy level. Upon initiation of therapy, average serum sodium concentrations increased to approximately the same levels as observed for those previously treated with tolvaptan and were sustained for at least a year. Figure 3 shows results from 111 patients enrolled in the SALTWATER Study. Figure 3: SALTWATER: Analysis of Mean Serum Sodium (± SD, mEq/L) by Visit
*p-value <0.0001 for all visits during tolvaptan treatment compared to baseline
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