Susan E. Shoaf

Pharmacokinetics, Pharmacodynamics, and Safety of Tolvaptan, a Nonpeptide AVP Antagonist, During Ascending Single‐Dose Studies in Healthy Subjects

Two single‐center, double‐blind, randomized, placebo‐controlled, sequentially enrolled studies were conducted. In study 1, 8 subjects (6 active/2 placebo) received 60‐, 90‐, 120‐, 180‐, or 240‐mg tolvaptan/matching placebo. In study 2, 9 subjects (6 active/3 placebo) received 180‐, 240‐, 300‐, 360‐, 420‐, or 480‐mg tolvaptan/matching placebo. Increases in tolvaptan Cmax were less than dose‐proportional and plateaued at doses greater than 240 mg; AUC∞ increased proportionally with dose. Changes in serum K+, creatinine clearance, and Na+, K+, and osmolality urinary excretion were similar to the placebo group for the 0‐ to 24‐hour interval following dosing. Changes were observed in plasma arginine vasopressin, serum aldosterone, and plasma renin activity but were not clinically significant. Increases were seen in mean serum Na+ concentrations (4–6 mEq/L), plasma osmolality (∼8 mOsm/kg), and free water clearance (∼6 mL/min) throughout 0 to 24 hours; none of these increases was dose dependent. Only total urine volume excretion (0–72 hours postdose) increased linearly with dose. As plasma tolvaptan concentrations increased, the duration that the urine excretion rate remained above baseline rates also increased. The most frequent adverse events—excess thirst, frequent urination, and dry mouth—appeared to be related to the pharmacological action of tolvaptan. No dose‐limiting toxicities were observed.

Tolerability and pharmacokinetics of aripiprazole in children and adolescents with psychiatric disorders: an open-label, dose-escalation study.

Abstract This multicenter, open-label, sequential-cohort, dose-escalation study explored the tolerability and pharmacokinetics (PK) of aripiprazole up to the maximum approved adult dose (30 mg/d) in children and adolescents (aged 10-17 years) preferentially with primary psychiatric diagnoses of a bipolar or schizophrenia spectrum disorder. During a dose-escalation phase, patients received aripiprazole for up to 12 days using forced titration to achieve doses of 20, 25, or 30 mg/d. In the subsequent fixed-dose phase, patients received the maximum dose for that cohort for an additional 14 days. Tolerability in each fixed-dose cohort was assessed by measures including evaluation of spontaneously reported adverse events (AEs) and vital signs. If 4 of 6 patients tolerated the maximum dose for the cohort, the dose was considered tolerated, and enrollment in the next dose level began. Of 21 enrolled patients, 17 completed the fixed-dose phase. Aripiprazole treatment was generally well tolerated, with criteria for tolerability met for all doses tested. All patients experienced at least 1 AE, none of which met the regulatory criteria for a serious AE. There were no deaths or clinically relevant changes in vital signs or weight. Aripiprazole PK seemed to be linear across the tested dose range and was comparable with previous PK observations in adults. This study provides information regarding the tolerability and PK of aripiprazole up to the maximum adult dose in children and adolescents. These data provided support for exploration of a 30-mg/d dose in child/adolescent schizophrenia and bipolar disorder.

Pharmacokinetic and pharmacodynamic interaction between tolvaptan, a non-peptide AVP antagonist, and furosemide or hydrochlorothiazide.

The pharmacokinetic and pharmacodynamic interactions between tolvaptan and furosemide or hydrochlorothiazide (HCTZ) were determined in a single-center, randomized, open-label, parallel-arm, 3-period crossover study conducted in healthy white (Caucasian) men. A total of 12 subjects were enrolled in the study, with 6 subjects assigned to each of two treatment arms. Subjects in Arm 1 received 30 mg of tolvaptan, 80 mg of furosemide, and 30 mg of tolvaptan + 80 mg of furosemide. Subjects in Arm 2 received 30 mg of tolvaptan, 100 mg of HCTZ, and 30 mg pf tolvaptan + 100 mg of HCTZ. Doses were separated by a 48-hour washout. Blood and urine samples were collected at scheduled timepoints during the 24 hours after administration of study drug for the determination of pharmacokinetic and pharmacodynamic parameters. No clinically significant changes were noted in the pharmacokinetic profiles of tolvaptan and furosemide or tolvaptan and HCTZ when coadministered. Free water clearance, 24-hour urine volume, plasma sodium and argentine vasopressin concentrations, and plasma osmolality were higher, and urine osmolality was lower when tolvaptan was administered either alone or in combination with furosemide or HCTZ, compared with furosemide or HCTZ administered alone. At 24 hours postdose, plasma renin activity was increased after furosemide or HCTZ administered alone or with tolvaptan, but it was unchanged after tolvaptan alone. Tolvaptan did not significantly affect the natriuretic activity of furosemide or HCTZ. Furosemide and HCTZ did not significantly affect the aquaretic activity of tolvaptan. Tolvaptan administered alone or in combination with furosemide or HCTZ was safe and well tolerated at the given doses.

Effects of CYP3A4 inhibition and induction on the pharmacokinetics and pharmacodynamics of tolvaptan, a non-peptide AVP antagonist in healthy subjects

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT Before these trials were done, the effects of CYP3A4 inhibition and induction on the pharmacokinetics (PK) and pharmacodynamics (PD) of tolvaptan in healthy subjects were unknown. As tolvaptan is a CYP3A4 substrate, knowing the effects of inhibition and induction on CYP3A4-mediated metabolism was important for dosing recommendations. WHAT THIS STUDY ADDS This paper describes the changes in tolvaptan PK and PD following inhibition or induction of CYP3A4 and explores the mechanisms behind the disparity seen between tolvaptan PK and effects on urine output. It also discusses the concentrations at which tolvaptan produces its maximal response on urine output and the timing of the onset and offset of this response. AIMS In vitro studies indicated CYP3A4 alone was responsible for tolvaptan metabolism. To determine the effect of a CYP3A4 inhibitor (ketoconazole) and a CYP3A4 inducer (rifampicin) on tolvaptan pharmacokinetics (PK) and pharmacodynamics (PD), two clinical trials were performed. METHODS For CYP3A4 inhibition, a double-blind, randomized (5:1), placebo-controlled trial was conducted in 24 healthy subjects given either a single 30 mg dose of tolvaptan (n= 19) or matching placebo (n= 5) on day 1 with a 72 h washout followed by a 3 day regimen of 200 mg ketoconazole, once daily with 30 mg tolvaptan or placebo also given on day 5. For CYP3A4 induction, 14 healthy subjects were given a single dose of 240 mg tolvaptan with 48 h washout followed by a 7 day regimen of 600 mg rifampicin, once daily, with 240 mg tolvaptan also given on the seventh day. RESULTS When co-administered with ketoconazole, mean C(max) and AUC(0,∞) of tolvaptan were increased 3.48- and 5.40-fold, respectively. Twenty-four hour urine volume increased from 5.9 to 7.7 l. Erythromycin breath testing showed no difference following a single dose of tolvaptan. With rifampicin, tolvaptan mean C(max) and AUC were reduced to 0.13- and 0.17-fold of tolvaptan administered alone. Twenty-four hour urine volume decreased from 12.3 to 8.8 l. CONCLUSIONS Tolvaptan is a sensitive CYP3A4 substrate with no inhibitory activity. Due to the saturable nature of tolvaptans effect on urine excretion rate, changes in the pharmacokinetic profile of tolvaptan do not produce proportional changes in urine output.

In Vitro P‐Glycoprotein Interactions and Steady‐State Pharmacokinetic Interactions Between Tolvaptan and Digoxin in Healthy Subjects

Interactions between tolvaptan and digoxin were determined in an open‐label, sequential study where 14 healthy subjects received tolvaptan 60 mg once daily (QD) on days 1 and 12 to 16 and digoxin 0.25 mg QD on days 5 to 16. Mean maximal concentrations (Cmax) and area under the curve during the dosing interval (AUCτ) for digoxin with tolvaptan (day 16) were increased 1.27‐ and 1.18‐fold compared with digoxin alone (day 11); mean renal clearance of digoxin was decreased by 59% (P < .05). Tolvaptan Cmax and AUC0–24h for a single dose with digoxin (day 12) were each increased about 10% compared with tolvaptan alone (day 1). Tolvaptan did not accumulate upon multiple dosing. After a single dose of tolvaptan (day 1, day 12), 24‐hour urine volume was about 7.5 L. As expected, after 5 days of tolvaptan, 24‐hour urine volume decreased about 20%. In vitro studies in control and MDR1‐expressing LLC‐PK1 cells indicate that tolvaptan is a substrate of P‐glycoprotein. Tolvaptan (50 μM) inhibited basolateral to apical digoxin secretion to the same extent as 30 μM verapamil; the IC50 of tolvaptan was determined to be 15.9 μM. The increase in steady‐state digoxin concentrations is likely mediated by tolvaptan inhibition of digoxin secretion.

Effects of Hepatic or Renal Impairment on the Pharmacokinetics of Aripiprazole

AbstractBackground and objectives: Two studies were conducted to investigate whether the pharmacokinetics of the atypical antipsychotic aripiprazole were altered in individuals with hepatic or renal impairment compared with those with normal hepatic or renal function. Study design: Two open-label, single-dose studies. Study setting: Clinical research unit. Patients: Study 1: Subjects with normal hepatic function (n = 6) and subjects with hepatic impairment (Child-Pugh class A [mild, n = 8], B [moderate, n = 8] or C [severe, n = 3]). Study 2: Subjects with normal renal function (creatinine clearance >80 mL/min; n = 7) and subjects with severe renal impairment (creatinine clearance <30 mL/min; n = 6). Treatment: Single oral dose of aripiprazole 15 mg. Pharmacokinetic analyses: Noncompartmental pharmacokinetic analysis was performed using plasma aripiprazole and dehydro-aripiprazole concentration-time data. Main outcome measures: Study 1 (hepatic impairment study): apparent oral clearance of unbound drug (CL/Fu) and the maximum plasma concentration (Cmax) of aripiprazole; Study 2 (renal impairment study): CL/Fu, Cmax and renal clearance (CLR). Safety assessments included 12-lead ECGs, vital sign monitoring, clinical laboratory measurements and assessment of adverse events.f Results: In the hepatic impairment study, the mean total Cmax of aripiprazole was significantly lower in subjects with severe hepatic impairment compared with those with normal hepatic function (p = 0.04). The fraction of aripiprazole unbound (fu) was significantly greater for subjects with mild (p = 0.02) or severe hepatic impairment (p<0.01) but not for those with moderate hepatic impairment (p = 0.09) compared with healthy controls. There were no meaningful differences in either the Cmax of unbound aripiprazole or CL/Fu between groups. The mean CLR of aripiprazole was negligible (0.04 mL/h/kg in controls and 0.19 mL/h/kg in patients with severe hepatic impairment). In the renal impairment study, the mean total Cmax values were numerically higher (∼40%) and the area under the plasma aripiprazole concentration-time curve from time zero to infinity was lower (∼19%) in renally impaired subjects versus those with normal renal function; the fu was comparable between groups. Aripiprazole CLR was ∼3-fold higher in renally impaired subjects, but this difference was not statistically significant. No deaths or serious adverse events were reported during either study. Conclusion: A single aripiprazole 15-mg dose was well tolerated. There were no meaningful differences in aripiprazole pharmacokinetics between groups of subjects with normal hepatic or renal function and those with either hepatic or renal impairment. Adjustment of the aripiprazole dose does not appear to be required in populations with hepatic or renal impairment.

Tolvaptan Administration Does Not Affect Steady State Amiodarone Concentrations in Patients With Cardiac Arrhythmias

Background: Tolvaptan, a nonpeptide selective vasopressin receptor (V2) antagonist, is in development for the treatment of congestive heart failure and hyponatremia. Tolvaptan is primarily metabolized via CYP3A4. This study was conducted to determine the extent of the pharmacokinetic interaction between tolvaptan and steady state amiodarone, an antiarrhythmic drug commonly prescribed for patients with congestive heart failure and a known inhibitor of other drugs metabolized by CYP3A4. Methods: This was a multicenter, open-label, 1-arm, 3-period, sequential treatment study conducted in 11 men (10) and women aged 49 to 80 years. They were primarily Caucasian (20) subjects, with a history of cardiac arrhythmias who were otherwise healthy. Subjects were to have been on oral amiodarone maintenance therapy of 200 mg/day for at least 10 months. All subjects took 200 mg amiodarone once daily on each study day; on days 3 and 4, they were also coadministered 30 and 90 mg of tolvaptan, respectively. The plasma concentrations of amiodarone and its metabolite desethylamiodarone were determined for 24 hours postdose on days 2, 3, and 4, tolvaptan concentrations were determined for 24 hours postdose on days 3 and 4. Results: As determined by the ratio of the geometric means and 90% confidence intervals (0.5 to 2.0) for the maximal plasma concentration and the area under the curve during the dosing interval for both amiodarone and desethylamiodarone, tolvaptan coadministration had no effect on either amiodarone and desethylamiodarone disposition, as all the geometric mean ratios (amiodarone + tolvaptan [30 or 90 mg] vs amiodarone alone) were approximately 1. Conclusion: Tolvaptan coadministration does not alter steady-state amiodarone or desethylamiodarone concentrations. Tolvaptan concentrations did not appear to be different from historical controls. The most frequently reported adverse event was polyuria (15 of 21 subjects for amiodarone + 30 mg tolvaptan); an expected outcome due to the known potent aquaretic action of tolvaptan. The combination of amiodarone and tolvaptan was well tolerated.

Comparison of two doses and dosing regimens of tolvaptan in congestive heart failure.

Fluid retention and extracellular volume expansion are frequently encountered complications of congestive heart failure (HF) that can cause morbidity and mortality. Tolvaptan (Otsuka) is an orally administered nonpeptide vasopressin (VP) V2 receptor antagonist that inhibits water reabsorption in the kidney by competitively blocking VP binding, resulting in water diuresis without significantly changing total electrolyte excretion. In the 24-hour period following a 30-mg dose of tolvaptan, urine excretion rate increases and declines as plasma concentrations rise and fall; this uneven effect results in 80% of daily urine output in the first 12 hours. Therefore, the current study was designed to assess the pharmacodynamic effects, pharmacokinetics, and clinical safety of tolvaptan 30 mg QD plus placebo versus 15 mg BID over 7 days in patients with NYHA Class II/III heart failure and persistent fluid overload, SBP ≥ 90 mm Hg, and a serum creatinine ≤ 3.0 mg/dL. Patients were withdrawn from diuretics for 48 hours before randomization. Statistics were performed with ANCOVA for continuous variables and Mantel-Haenszel mean score test stratified by center for categorical variables. Thirty-nine of 40 patients completed days 1 and 7. There were no significant clinical, pharmacokinetic, or pharmacodynamic differences between the dosing regimens over time. Based on these findings, tolvaptan 30 mg was chosen as the comparator for placebo in a large phase 3 survival trial.

Pharmacokinetics and pharmacodynamics of oral tolvaptan in patients with varying degrees of renal function.

The selective vasopressin V2–receptor antagonist tolvaptan is eliminated almost exclusively by non-renal mechanisms. As renal impairment can influence the pharmacokinetics of drugs even when eliminated by non-renal mechanisms, we evaluated the effect of renal insufficiency on the pharmacokinetics/pharmacodynamics of tolvaptan. Thirty-seven patients were grouped by a 24-h creatinine clearance (CrCL) and evaluated for 48 h after a single 60 mg oral dose in the fasting state. Mean tolvaptan exposure was 90% higher in the under 30-ml/min group compared with the over 60-ml/min group with individual values significantly but negatively correlated with increasing baseline CrCL. There was a greater and more rapid increase in urine output and free water clearance in the over 60-ml/min compared with the renal impaired groups, but they returned to baseline more quickly. Serum sodium increased more rapidly in the over 60 as opposed to the under 30-ml/min group, but overall maximum increases were similar across groups. Small decreases in mean CrCL and small increases in mean serum creatinine/potassium were independent of baseline CrCL. The percent fractional free water clearance with respect to CrCL was significantly but negatively correlated with increasing baseline CrCL. No unexpected adverse events were reported. Thus, renal impairment attenuated the increase in 24-h urine volume and free water clearance caused by tolvaptan, consistent with decreased nephron function in renal impairment. The delay in serum sodium increase was consistent with the longer duration needed to excrete sufficient water to cause the increase.

Absolute bioavailability of tolvaptan and determination of minimally effective concentrations in healthy subjects.

Tolvaptan is a selective vasopressin V2 receptor antagonist that can be given orally once daily for treatment of clinically significant hypervolemic and euvolemic hyponatremia (US) or cardiac edema (Japan). Tolvaptan absolute bioavailability was determined in a single-center, open-label, sequential administration trial in which intravenous (i.v.) placebo (Day -2), i.v. 1 mg tolvaptan (Day 1) and an oral 30 mg tablet (Day 8) were administered to 14 healthy subjects. Urine volume and osmolality were determined on Days -2, 1 and 8 at multiple intervals postdose; 24-h fluid balance was also assessed. On Days 1 and 8, blood samples for tolvaptan were collected for 48 h postdose. Mean absolute bioavailability was determined to be 56% (range 42 - 80). Mean peak tolvaptan concentration at 1 h (end-of-infusion) was 32.7 (range 18 - 45) ng/ml compared to 231 (range 87 - 410) ng/ml for the oral dose. In the 4-h period from start of the 1 mg tolvaptan i.v. infusion, 12 of 14 subjects experienced increased urine volume and decreased urine osmolality; both parameters were affected for 24 h postdose following the 30 mg oral dose. Minimally effective concentrations are rapidly achieved after oral dosing as all subjects had tolvaptan concentrations > 20 ng/ml at 1 h postdose.