Population Pharmacokinetic Modeling and Exposure-Response Analysis for Aripiprazole Once Monthly in Subjects With Schizophrenia

An intramuscular formulation of aripiprazole monohydrate dosed once monthly (AOM) was developed to address nonadherence with the approved oral tablets. A 3-compartment linear population pharmacokinetic model for oral and AOM doses was developed; relative bioavailability was estimated for AOM relative to oral dosing and body mass index and sex were significant predictors of AOM absorption rate constant (longer absorption half-life for women and absorption half-life increases with increasing body mass index). Aripiprazole apparent oral clearance for subjects with cytochrome P450 (CYP) 2D6 poor metabolizer status and in the presence of strong CYP2D6 inhibitors was approximately half that of subjects with CYP2D6 extensive metabolizer status and 24% lower in the presence of strong CYP3A4 inhibitors. Simulations of the population pharmacokinetics were conducted to evaluate the effect of different dose initiation strategies for AOM, the effects of CYP2D6 metabolizer status, coadministration of CYP2D6 and CYP3A4 inhibitors, and missed doses. An exposure-response model with an exponential hazard function of the model-predicted minimum concentration (C_min ) described the time to relapse. The hazard ratio (95% confidence interval) was 4.41 (2.89-6.75). Thus, a subject with a diagnosis of schizophrenia and C_min  ≥ 95 ng/mL is 4.41 times less likely to relapse relative to a subject with C_min  < 95 ng/mL.

An Integrated Pharmacokinetic-Pharmacodynamic-Pharmacoeconomic Modeling Method to Evaluate Treatments for Adults with Schizophrenia

INTRODUCTION

Schizophrenia is a chronic mental disorder that worsens with each relapse. Long-acting injectable (LAI) antipsychotics may prevent the exacerbation of symptoms and occurrence of relapses through improved continuity of care. Different dose regimens are available for the LAIs aripiprazole monohydrate (AM) and aripiprazole lauroxil (AL), but their cost effectiveness is unclear.

OBJECTIVES

The study aim was to compare costs and effects (relapses) of the different aripiprazole LAI dose regimens to inform clinical and US payer decisions.

METHODS

A state-transition model calculated the outcomes of eight LAI dose regimens based on their relapse rates. As effectiveness data from randomized controlled trials were unavailable, relapse rates were modeled using pharmacokinetic and pharmacodynamic evidence. These described blood plasma levels of aripiprazole as a function of AM and AL dose regimens and described the probability of relapse as a function of aripiprazole blood plasma levels. The analysis had a time horizon of 1 year and took the US healthcare payer perspective. The incremental cost per relapse avoided and the probability of cost effectiveness were calculated in deterministic and probabilistic analyses. Scenario analyses explored the model's main assumptions, and results were validated against external data and other cost-effectiveness analyses.

RESULTS

Monthly administration of AM 400 mg consistently yielded the lowest predicted number of relapses across deterministic, probabilistic, and scenario analyses. The costs of treatment and relapses were projected to be the lowest with a monthly administration of AL 441 mg. The incremental cost per relapse avoided with AM 400 mg ranged from AM 400 mg being dominant to $US83,300. From willingness-to-pay thresholds of $US30,000 per relapse avoided, the probability of cost effectiveness was highest for AM 400 mg. The validation showed alignment with external data.

CONCLUSION

The analysis highlighted the robustness of the novel framework based on pharmacokinetic and pharmacodynamic evidence and demonstrated an application in a postmarketing setting.

Cytomegalovirus Antibody Responses Associated With Increased Risk of Tuberculosis Disease in Ugandan Adults

BACKGROUND

Recent evidence highlights human cytomegalovirus (HCMV) and immune activation as risk factors for tuberculosis disease. It is not known whether other herpesviruses are also implicated, nor whether a dose-response relationship exists between tuberculosis risk and herpes coinfection.

METHODS

This nested case-control study used stored serum samples from 25 persons with tuberculosis up to 10 years before tuberculosis diagnosis and between 3 and 6 matched controls without tuberculosis from a rural Ugandan cohort. Samples were investigated for Epstein-Barr virus, herpes simplex virus, and HCMV-specific immunoglobulin G (IgG), serum markers of inflammation, and mycobacterial antibody levels.

RESULTS

Humoral response to HCMV, but not Epstein-Barr or herpes simplex virus, was associated with increased risk of active tuberculosis disease up to 10 years before diagnosis. Individuals with medium HCMV IgG were 2.8 times more likely to have tuberculosis (P = .055), and those with high HCMV IgG 3.4 times more likely to have tuberculosis (P = .007). Mycobacterial antibody levels were not associated with differences in odds of tuberculosis disease. Interferon-induced protein 10 was independently associated with increased odds of tuberculosis (odds ratio, 4.2; P = .009).

CONCLUSIONS

These data provide evidence of a dose response between magnitude of HCMV IgG with risk of tuberculosis disease. An inflammatory environment, characterized by serum interferon-induced protein 10 and interleukin 1α, is independently associated with increased risk of tuberculosis disease.

Pharmacokinetic and Pharmacodynamic Interaction Between Tolvaptan and Warfarin in Healthy Subjects

PURPOSE

Tolvaptan, a nonpeptide V2 receptor antagonist approved in Japan and in the United States, is likely to be co-administered with warfarin in patients with heart failure (HF). Therefore, the effect of tolvaptan on warfarin pharmacokinetics, pharmacodynamics, and protein binding was evaluated.

METHODS

An open-label, randomized, 2-period crossover trial was conducted involving healthy subjects (N = 24) administered 25 mg warfarin sodium on day 4 of a 13-day regimen of either 60 mg once daily tolvaptan or matching placebo. Blood samples were taken over 240 hours postdose for analysis of tolvaptan, R- and S-warfarin, and 7- and 10-hydroxywarfarin concentrations and for the measurement of activated partial thromboplastin time, prothrombin time, and international normalized ratio.

RESULTS

For S-warfarin, the geometric mean ratios (warfarin+tolvaptan/warfarin alone; 90% confidence interval) for maximum plasma concentration (Cmax ) and area under the concentration-time curve from time 0 to infinity (AUC∞ ) were 1.09 (1.05, 1.12) and 1.09 (1.04, 1.13), respectively. Corresponding ratios for R-warfarin were 1.06 (1.02, 1.09) and 1.05 (1.01, 1.11), respectively. No changes were observed in 7- or 10-hydroxywarfarin Cmax or AUC∞ values, prothrombin time, activated partial thromboplastin time, and international normalized ratio. The protein binding of racemic warfarin and tolvaptan was not significantly altered by the presence of the other compound.

CONCLUSION

Warfarin doses do not need to be altered when co-administered with tolvaptan.

Population-based meta-analysis of hydrochlorothiazide pharmacokinetics

Hydrochlorothiazide (HCTZ) is a thiazide diuretic used for the treatment of hypertension and edema associated with fluid overload conditions such as congestive heart failure (CHF). A population-based meta-analysis approach in NONMEM® was used to develop a PK model to characterize the time-course of HCTZ concentrations in plasma and excretion into the urine for healthy subjects and CHF patients. Data from healthy subjects receiving 100 mg of oral HCTZ were supplemented with additional plasma concentration and urinary excretion versus time data published in the literature following administration of oral HCTZ doses ranging from 10 to 500 mg to healthy subjects or patients with renal failure, CHF or hypertension. A two-compartment model with first-order oral absorption, using a Weibull function, and first-order elimination best described HCTZ PK. Creatinine clearance (CLCR ) was a statistically significant predictor of renal clearance (CLR ). Non-renal clearance was estimated to be 2.44 l/h, CLR was 18.3 l/h and T1/2,α was 1.6 h and T1/2,β was 14.8 h for a typical individual with normal renal function (CLCR  = 120 ml/min). However, CLR was reduced to 10.5, 5.47 and 2.70 l/h in mild (CLCR  = 80 ml/min), moderate (CLCR  = 50 ml/min) and severe (CLCR  = 30 ml/min) renal impairment, respectively. Model diagnostics helped to demonstrate that the population PK model reasonably predicts the rate of urinary HCTZ excretion over time using dosing history and estimated CLCR , allowing for the convenient assessment of PK-PD relationships for HCTZ when given alone or in combination with other agents used to treat fluid overload conditions.

Safety and tolerability of once monthly aripiprazole treatment initiation in adults with schizophrenia stabilized on selected atypical oral antipsychotics other than aripiprazole

OBJECTIVE

Safety and tolerability assessment of initiating treatment with a once monthly long-acting injectable form of aripiprazole (aripiprazole once monthly) in patients stabilized on oral antipsychotics other than aripiprazole.

METHODS

Patients with schizophrenia treated with oral atypical antipsychotics other than aripiprazole and with a history of aripiprazole tolerability were enrolled. Patients were stabilized per investigator's judgment for ≥14 days on oral atypical antipsychotics during screening. Patients then received one dose of aripiprazole once monthly (400 mg). Concomitant with aripiprazole once monthly, subjects received their current oral atypical antipsychotic for 14 ± 1 days at doses reduced to the mid/lower recommended dose range. Safety and tolerability were assessed for the 28-day treatment phase. For pharmacokinetic analyses, aripiprazole plasma concentrations were measured on Days 7, 14, and 28.

RESULTS

Sixty patients were enrolled and initiated with aripiprazole once monthly while continuing treatment with oral olanzapine (n = 3), quetiapine (n = 28), risperidone (n = 24) or ziprasidone (n = 5). Duration of co-administered oral antipsychotic treatment varied, ranging from 0 to 15 days. Treatment was well tolerated. Frequently reported treatment-emergent adverse events (TEAEs) were injection-site pain and toothache (4/60 subjects each, 6.7%), followed by dystonia, fatigue, increased blood creatine phosphokinase, insomnia and restlessness (3/60 subjects each, 5.0%). Most TEAEs occurred in the first 8 days of co-administration irrespective of days of oral overlap. No clinically relevant mean changes from baseline were observed for laboratory values or fasting metabolic parameters. Psychotic symptoms remained stable. Aripiprazole plasma concentrations were similar to those observed following daily doses of oral aripiprazole.

CONCLUSIONS

The adverse-event profile of patients receiving aripiprazole once monthly concomitant with oral atypical antipsychotics other than aripiprazole was consistent with previous reports of aripiprazole once monthly concomitant with oral aripiprazole. Adverse events were similar irrespective of prior atypical antipsychotic and duration of oral antipsychotic overlap, suggesting that patients can be safely switched from their existing oral antipsychotic to aripiprazole once monthly without requiring an intermediate stabilization phase with oral aripiprazole. Aspects of the study design (open-label trial and short duration) and patient population (predominantly male and of African-American ethnicity) may limit the generalizability of these findings.

CLINICAL TRIAL REGISTRATION

Safety and Tolerability Trial of Aripiprazole IM Depot Treatment in Adult Subjects With Schizophrenia Stabilized on Oral Antipsychotics Other Than Aripiprazole. ID number: NCT01552772. Registry: clinicaltrials.gov.

Pharmacokinetics, tolerability and safety of aripiprazole once-monthly in adult schizophrenia: an open-label, parallel-arm, multiple-dose study

This 24-week, open-label, Phase Ib, parallel-arm, multiple-dose trial assessed the pharmacokinetics, safety and tolerability of a once-monthly injection of aripiprazole (aripiprazole once-monthly) in 41 subjects with schizophrenia. The objective was to determine if aripiprazole plasma concentrations (at doses of 200, 300 and 400mg) were within the therapeutic range observed for the oral tablet (10-30 mg). Completion rates were 36.4% (n=4/11), 50.0% (n=8/16) and 71.4% (n=10/14) for the 200mg, 300 mg and 400mg groups, respectively. Patients were stabilized on oral aripiprazole (10mg/day) before the first injection and received oral aripiprazole (10mg/day) concomitantly with the first dose of aripiprazole once-monthly for 14 days. Administration of aripiprazole once-monthly at doses of 300 and 400mg provided sustained mean aripiprazole plasma concentrations comparable with the concentration range observed following multiple consecutive daily doses of oral aripiprazole. In contrast, plasma concentrations following administration of aripiprazole once-monthly at a dose of 200mg were below the therapeutic range and pharmacokinetic parameters were not proportional to the administered dose compared with the 300 mg and 400mg doses. Treatment with aripiprazole once-monthly, at any dose, did not result in any clinically meaningful changes from baseline in extrapyramidal symptom scales, clinical laboratory tests, vital signs, or electrocardiogram parameters. The most common treatment-emergent adverse events were vomiting (13.3%, 300 mg; 14.3%, 400mg), injection site pain (28.6%, 400mg), upper respiratory tract infection (10%, 200mg; 6.7% 300 mg; 14.3%, 400mg) and tremor (6.7%, 300 mg; 21.4%, 400mg). In conclusion, aripiprazole once-monthly at doses of 300 and 400mg is a viable formulation for treatment of adults with schizophrenia.

Population pharmacokinetics of tolvaptan in healthy subjects and patients with hyponatremia secondary to congestive heart failure or hepatic cirrhosis

Tolvaptan is a selective V2 -receptor antagonist used to treat hypervolemic and euvolemic hyponatremia. A population pharmacokinetic (PK) analysis was performed for tolvaptan in NONMEM® based upon data obtained from three trials conducted in 93 healthy subjects and six trials conducted in 628 congestive heart failure (CHF) patients or 24 hepatic cirrhosis patients receiving oral tolvaptan (5 to 240 mg). A two-compartment model with first-order absorption and elimination best described tolvaptan PK. Relative oral bioavailability was modeled relative to 100% for a 30 mg dose and ranged from 79.4% to 122%. Body weight and the impact of CHF or hepatic cirrhosis relative to healthy subjects were statistically significant (p < 0.001) predictors of both the apparent oral clearance (CL/F) and apparent central volume of distribution (Vc /F). The CL/F was reduced to 58.2% for New York Heart Association (NYHA) Class 1 or 2 CHF, 45.5% for NYHA Class 3 or 4 CHF, and 58.0% for hepatic cirrhosis relative to healthy subjects. Vc /F was reduced to 59.9% for NYHA Class 1 or 2 CHF and 51.3% for NYHA Class 3 or 4 CHF, and was 64.8% larger for severe hepatic cirrhosis (Child-Pugh score ≥ 10) relative to healthy subjects. A slight additional decrease in CL/F of 18.3% was also detected for patients with moderate hyponatremia (serum sodium of 115-130 mEq/l) after adjusting for CHF or cirrhosis (p < 0.001). This population PK model enabled assessment of tolvaptan PK with varying degrees of CHF and hepatic cirrhosis with fluid overload and may be used to explore PK-PD relationships with respect to fluid and electrolyte balance.

Pharmacokinetics, Tolerability, and Safety of Aripiprazole following Multiple Oral Dosing in Normal Healthy Volunteers

Two 14-day, placebo-controlled, double-blind studies evaluated the fasting pharmacokinetics, safety, and tolerability of aripiprazole, a new antipsychotic, in healthy male subjects. In Study 1, 37 subjects were randomized to aripiprazole 5 mg, 10 mg, 15 mg, 20 mg, or placebo once daily. In Study 2, 11 subjects were randomized to aripiprazole, titrated from 10 to 30 mg/day, or placebo. Aripiprazole had linear pharmacokinetics over 5 to 30 mg/day, which were described by a two-compartment open model, with first-order absorption. In Study 1, mean elimination half-life ranged from 47 to 68 hours with aripiprazole, with apparent systemic clearance (CL/F) of approximately 3.45 L/h. In Study 2, mean elimination half-life was 59 hours (CL/F approximately 4.0 L/h). Adverse events were generally mild to moderate, were transient in nature, and commonly occurred within the first 3 days of dosing. Clinical laboratory assessments, electrocardiogram, electroencephalogram, and prolactin levels showed no clinically significant changes during the studies.

Pharmacokinetics of Aripiprazole and Concomitant Lithium and Valproate

The objective of this study was to assess the pharmacokinetics of the antipsychotic aripiprazole when coadministered with lithium or valproate. Two open-label, sequential treatment design studies were conducted in chronically institutionalized patients with schizophrenia or schizoaffective disorder requiring treatment with lithium (n = 12) or valproate (divalproex sodium) (n = 10). Patients received aripiprazole 30 mg/day on days 1 to 14 and aripiprazole with concomitant therapy on days 15 to 36. Lithium was titrated from 900 mg until serum concentrations reached 1.0 to 1.4 mEq/L for at least 5 days. Valproate was titrated to 50 to 125 mg/L. Coadministration with lithium increased mean Cmax and AUC values of aripiprazole by about 19% and 15%, respectively, whereas the apparent oral clearance decreased by 15%. There was no effect on the steady-state pharmacokinetics of the active metabolite of aripiprazole. Coadministration with valproate decreased the AUC and Cmax of aripiprazole by 24% and 26%, respectively, with minimal effects on the active metabolite. Therapeutic doses of lithium and divalproex had no clinically significant effects on the pharmacokinetics of aripiprazole in patients with schizophrenia or schizoaffective disorder.

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 tolvaptan's effect on urine excretion rate, changes in the pharmacokinetic profile of tolvaptan do not produce proportional changes in urine output.

The pharmacokinetics of standard antidepressants with aripiprazole as adjunctive therapy: studies in healthy subjects and in patients with major depressive disorder

Possible effects of the atypical antipsychotic aripiprazole on the pharmacokinetics of standard antidepressant therapies (ADTs) were assessed in two open-label, non-randomised studies in healthy subjects (Studies 1 and 2) and two placebo-controlled studies in patients with major depressive disorder (MDD) (Studies 3 and 4). Healthy subjects received venlafaxine 75 mg/day (Study 1; N = 38) or escitalopram 10 mg/ day (Study 2; N = 25) with the addition of aripiprazole 10-20 mg/day (10 mg/day fixed dose in Study 2) for 14 days. Patients with MDD (N = 498; Studies 3 and 4) received escitalopram (10-20 mg/day), fluoxetine (20-40 mg/day), paroxetine controlled-release (37.5-50 mg/day), sertraline (100-150 mg/day) or venlafaxine extended-release (150-225 mg/day) for 8 weeks plus placebo. Incomplete responders were randomised (1:1) to placebo or adjunctive aripiprazole 2-20 mg/day. Blood samples were collected for pharmacokinetic analysis of ADTs. Plasma concentration-time data from Studies 3 and 4 were combined for statistical analysis. In healthy subjects, point estimates [90% CI] for the ratios of geometric means of C( max) (venlafaxine 1.148 [1.083-1.217]; escitalopram 1.04 [0.99-1.09]) and AUC(TAU) (venlafaxine 1.183 [1.130-1.238]; escitalopram 1.07 [1.04-1.11]) indicated no meaningful increase in ADT exposure in the presence of aripiprazole. In patients, point estimates for mean plasma concentration ratios indicated no substantial effect of aripiprazole on any ADT escitalopram 0.970 [0.911-1.033], fluoxetine 1.177 [1.049-1.321], paroxetine 0.730 [0.598-0.892], sertraline 0.958 [0.887-1.035] or venlafaxine 0.966 [0.887-1.051]. Aripiprazole had no meaningful effects on the pharmacokinetics of standard ADTs in either healthy subjects or patients with MDD.

An open-label study of aripiprazole: pharmacokinetics, tolerability, and effectiveness in children and adolescents with conduct disorder

OBJECTIVES

This study evaluated flexible-dose pharmacokinetics, safety, and effectiveness of aripiprazole in children and adolescents with conduct disorder (CD).

METHODS

This open-label, 15-day, three-center study with an optional 36-month extension enrolled a total of 23 patients: 12 children (6-12 years) and 11 adolescents (13-17 years) with CD and a score of 2-3 on the Rating of Aggression Against People and/or Property (RAAPP). Initially, the protocol used the following dosing: subjects <25 kg, 2 mg/day; subjects 25-50 kg, 5 mg/day; subjects >50-70 kg, 10 mg/day; and subjects >70 kg, 15 mg/day. Due to vomiting and sedation, this schedule was revised to: <25 kg, 1 mg/day; 25-50 kg, 2 mg/day; >50-70 kg, 5 mg/day; and >70 kg, 10 mg/day.

RESULTS

Aripiprazole pharmacokinetics were linear, and steady state appeared to be attained within 14 days. Both groups demonstrated improvements in RAAPP scores and Clinical Global Impressions-Severity (CGI-S) scores. Adverse events were similar to the known profile for aripiprazole in adults.

CONCLUSION

The pharmacokinetics of aripiprazole in children and adolescents are linear and comparable with those in adults. Aripiprazole was generally well-tolerated in patients with CD, particularly after protocol adjustments, with improvements in aggressive behavior.

A non-randomized study to investigate the effects of the atypical antipsychotic aripiprazole on the steady-state pharmacokinetics of lamotrigine in patients with bipolar I disorder

OBJECTIVE

To determine the effect of aripiprazole on steady-state pharmacokinetics of lamotrigine in patients with bipolar I disorder who were clinically stable on lamotrigine (100-400 mg/day) for >or=4 weeks.

METHODS

In this open-label study, aripiprazole was administered at 10 mg/day for 3 days, 20 mg/day for 3 days, then 30 mg/day for 8 days. Blood samples were collected on Days -1 and 14 for determination of lamotrigine steady-state pharmacokinetic parameters. Safety and tolerability were assessed.

RESULTS

Eighteen patients were administered aripiprazole in combination with lamotrigine. Geometric mean (GM) values for lamotrigine maximum plasma concentration were similar for lamotrigine alone (26 ng/mL) and with co-administered aripiprazole (23 ng/mL). GM values for plasma lamotrigine area under the concentration-time curve (AUCtau) were comparable for lamotrigine alone (434 ng/h/mL) and with co-administered aripiprazole (394 ng/h/mL). Median T(max) of lamotrigine alone and combined with aripiprazole was 1.98 and 0.77 h, respectively. No changes to lamotrigine dose-normalized plasma trough concentrations were observed with co-administered aripiprazole. Sixteen patients (88.9%) experienced >or=1 adverse event (AE), the most common of which was insomnia (n = 6).

CONCLUSIONS

Aripiprazole had no meaningful effect on lamotrigine steady-state pharmacokinetics in patients with bipolar I disorder. No dosage adjustment of lamotrigine is required and the combination was generally safe and well tolerated.

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 C(max) were less than dose-proportional and plateaued at doses greater than 240 mg; AUC(infinity) 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 ( approximately 8 mOsm/kg), and free water clearance ( approximately 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.

Pharmacokinetics of aripiprazole and concomitant carbamazepine

The objective of this study was to assess the pharmacokinetics of aripiprazole when coadministered with carbamazepine using an open-label sequential treatment design in patients with schizophrenia or schizoaffective disorder. Nine male patients were enrolled and received aripiprazole monotherapy (30 mg once daily) for 14 days, after which aripiprazole steady-state pharmacokinetics were assessed. Subjects were then administered carbamazepine together with aripiprazole for 4 to 6 weeks. The dose of carbamazepine was titrated to produce a trough serum concentration within the range of 8 to 12 mg/L. Aripiprazole pharmacokinetics were then assessed in the presence of carbamazepine. Six patients completed the study as designed. Coadministration with carbamazepine decreased the values of mean peak plasma concentration and area under the plasma concentration-time curve of aripiprazole by 66% and 71%, respectively (P = 0.001 and 0.002, respectively). Similarly, coadministration with carbamazepine decreased the values of mean peak plasma concentration and area under the plasma concentration-time curve over the 24-hour dosing interval of the major active metabolite of aripiprazole, dehydroaripiprazole, by 68% and 69%, respectively (P < 0.001). Both aripiprazole and dehydroaripiprazole are substrates for the cytochrome P-450 3A4 enzyme which is known to be induced by carbamazepine dosed to steady state. Thus, therapeutic doses of carbamazepine had significant effects on the pharmacokinetics of aripiprazole in patients with schizophrenia or schizoaffective disorder. When carbamazepine is added to aripiprazole therapy, aripiprazole dose should be doubled (to 20-30 mg/d). Additional dose increases should be based on clinical evaluation. When carbamazepine is withdrawn from combination therapy, aripiprazole dose should then be reduced.

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 > or = 90 mm Hg, and a serum creatinine < or = 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.

Phase I and pharmacokinetic study of the differentiating agent vesnarinone in combination with gemcitabine in patients with advanced cancer

PURPOSE

To evaluate the maximum-tolerated dose, dose-limiting toxicities (DLTs), and pharmacokinetic profile of vesnarinone given once daily in combination with gemcitabine.

PATIENTS AND METHODS

Twenty-six patients were treated with oral vesnarinone once daily on a continuous schedule at doses of 60, 90, 120, 150, and 180 mg in combination with intravenous (IV) gemcitabine at a dose of 1,000 mg/m(2) on days 1, 8, and 15 every 4 weeks. To determine whether biologically relevant concentrations were being achieved, predose concentrations (C(min)) of vesnarinone were obtained weekly. Plasma gemcitabine and 2',2'-difluorodeoxyuridine concentrations were obtained during courses 1 and 2.

RESULTS

Twenty-six patients were treated with 92 courses of vesnarinone/gemcitabine. The principal toxicities of the regimen consisted of neutropenia and thrombocytopenia, which were dose-limiting in two of eight heavily pretreated new patients treated at the 90 mg/1,000 mg/m(2) dose level and one of 10 minimally pretreated new patients at the 120 mg/1,000 mg/m(2) dose level. None of three patients treated with 15 courses at the vesnarinone/gemcitabine dose levels of 60 mg/1,000 mg/m(2) experienced DLT. Pharmacokinetic studies of vesnarinone revealed significant interpatient variability at any given dose level. There was evidence of a linear relationship between vesnarinone dose and mean C(min) at dosages of vesnarinone less than 150 mg, with plateauing of mean C(min) values at higher dosages. There was no impact of vesnarinone on gemcitabine concentrations, and the vesnarinone pharmacokinetics did not change with gemcitabine between weeks 1 and 2. Two partial responses occurred in patients with refractory breast and non-small-cell lung carcinoma.

CONCLUSION

When combined with gemcitabine, the recommended dose of vesnarinone for phase II evaluations is 90 mg orally once daily with gemcitabine 1,000 mg/m(2) IV on days 1, 8, and 15 every 4 weeks. There is no evidence of pharmacokinetic interaction between vesnarinone and gemcitabine. Further studies of vesnarinone as a single agent or in combination with gemcitabine and other antineoplastic agents are warranted.

Cilostazol pharmacokinetics after single and multiple oral doses in healthy males and patients with intermittent claudication resulting from peripheral arterial disease

OBJECTIVE

To study the pharmacokinetics of cilostazol following single oral administration of 50 to 200 mg in healthy young males, and after repeated oral administration of 100 mg every 12 hours to patients with peripheral arterial disease (PAD).

DESIGN

The healthy male single dose study was a single-centre, randomised sequence, open-label, incomplete block, 3-period, 4-treatment, crossover design. The patient study was a single-centre, multiple dose, open-label study.

STUDY PARTICIPANTS

20 healthy nonsmoking male volunteers were enrolled and successfully completed the single dose study. 26 patients (21 males, 5 females) with intermittent claudication resulting from PAD were enrolled and completed the single/multiple dose study.

MAIN OUTCOME MEASURES

Noncompartmental pharmacokinetic parameters, the area under the plasma concentration-time curve from zero to the time of last measurable plasma concentration, and maximum plasma concentration.

RESULTS

Peak plasma concentrations of cilostazol occurred about 3 hours after drug administration and then declined biexponentially with concentrations detectable (> 20 micrograms/L) in the plasma for at least 36 hours postdose. The apparent elimination half-life of cilostazol (approximately 11 hours) was similar after a single dose or after multiple doses, with steady state being reached within 4 days. Cilostazol accumulated 1.7-fold following multiple dose administration. The apparent volume of distribution (Vz/F; 2.76 L/kg) suggested extensive distribution of cilostazol in the tissues. The oral clearance of cilostazol (CL/F; 0.18 L/h/kg) was much lower than liver blood flow, indicating a low extraction ratio drug, and hence low probability of a significant first-pass effect. None of the administered doses were recovered in the urine as unchanged cilostazol, suggesting that metabolism, rather than urinary excretion, is the major elimination route. Following single oral doses of 50 to 200 mg, the plasma concentrations of cilostazol and its metabolites increased less than proportionally to the dose. The pharmacokinetics of cilostazol in normal healthy volunteers are predictive of those in patients with PAD. Single oral doses of 50 to 200 mg cilostazol as well as 100 mg cilostazol every 12 hours were well tolerated.

CONCLUSION

The plasma concentration of cilostazol and its metabolites increased less than proportionally with increasing doses. The relatively low plasma clearance and high volume of distribution of cilostazol suggest a low first-pass effect and extensive distribution. The pharmacokinetics of cilostazol in normal volunteers is predictive of that in patients with PAD. Cilostazol was well tolerated in healthy volunteers and patients with intermittent claudication resulting from PAD.

Effect of cilostazol on the pharmacokinetics and pharmacodynamics of warfarin

OBJECTIVE

To evaluate the effect of cilostazol administration on warfarin pharmacokinetics and pharmacodynamics following a single 25 mg dose of warfarin.

DESIGN

A randomised double-blind 2-period crossover with healthy volunteers receiving either 100 mg cilostazol twice daily for 13 days or matching placebo twice daily for 13 days, and the other treatment 21 days later. A single 25 mg dose of warfarin was given 14 days prior to the start of the study, and 7 days after the cilostazol and placebo treatments.

STUDY PARTICIPANTS

15 normal healthy male volunteers.

OUTCOME MEASURES

Noncompartmental pharmacokinetic parameters for (R)- and (S)-warfarin, the area under the curve of the prothrombin time (AUCPT), activated partial thromboplastin time (AUCaPTT), Ivy bleeding times, unbound fraction (fu) of cilostazol, and warfarin were determined for each individual.

RESULTS

For (R)- and (S)-warfarin, the 90% confidence intervals for the ratios of the geometric means (90% CI) of the maximum plasma concentration and area under the plasma concentration-time curve were between 0.88 to 1.03. The 90% CI for the AUCPT and AUCaPTT was between 0.95 and 1.06. For Ivy bleeding time, the 90% CI for the ratios of the geometric means ranged between 0.71 and 1.22. The fu of cilostazol did not differ significantly between the 2 treatments. There was a 17% increase in the fu of warfarin (p < 0.05), which was not clinically significant.

CONCLUSIONS

Coadministration of warfarin with twice daily administration of cilostazol 100 mg did not alter (R)- and (S)-warfarin pharmacokinetics, prothrombin time, partial thromboplastin time, Ivy bleeding times, or cilostazol protein binding.

Interaction potential and tolerability of the coadministration of cilostazol and aspirin

OBJECTIVE

This study evaluated the effects of repeated oral drug administration with cilostazol alone and with aspirin (acetylsalicylic acid) on platelet aggregation, coagulation and bleeding time as well as the cilostazol-aspirin pharmacokinetic interaction in healthy males.

DESIGN

This was a randomised, double-blind, placebo-controlled, crossover study. Participants received either cilostazol 100 mg or placebo twice a day for 10 days; aspirin 325 mg/day was coadministered for the last 5 days. After a 14-day washout period, participants received the alternative treatment.

STUDY PARTICIPANTS

12 healthy male volunteers were enrolled.

MAIN OUTCOME MEASURES

Differences in bleeding times, platelet aggregation, prothrombin time (PT) and activated partial thromboplastin time (aPTT) between cilostazol with aspirin and cilostazol alone. Noncompartmental pharmacokinetic parameters were determined for each study participant.

RESULTS

Cilostazol, with or without aspirin, caused no changes in PT, aPTT or bleeding time. There was a 23 to 35% increase in inhibition of ADP-induced ex vivo platelet aggregation by cilostazol plus aspirin when compared with aspirin alone. There was no additive or synergistic effect on arachidonic acid-induced platelet aggregation. Statistically significant but clinically insignificant increases in the area under the plasma concentration-time curve to the last measurable plasma concentration and trough concentrations of cilostazol and its metabolites (OPC-13015 and OPC-13213) occurred after aspirin coadministration, with no differences observed in the maximum plasma concentration Drug-related adverse events were generally mild, the most frequent being headache.

CONCLUSIONS

Cilostazol and aspirin coadministration did not cause clinically significant changes in PT, aPTT, bleeding time, platelet aggregation or plasma concentrations of cilostazol and its 2 active metabolites. Cilostazol was generally well tolerated with or without aspirin.

Effect of renal impairment on the pharmacokinetics of cilostazol and its metabolites

OBJECTIVE

The pharmacokinetics of cilostazol were studied in patients with mild, moderate and severe renal impairment and in healthy volunteers after administration of 50 mg single and multiple doses of cilostazol.

DESIGN

This was an open-label, single and multiple dose study administering 50 mg cilostazol every 12 hours to healthy volunteers and patients with varying degrees of renal impairment.

PARTICIPANTS

6 normal volunteers [creatinine clearance (CLCR) > or = 90 ml/min]; 6 patients with mild (CLCR 50 to 89 ml/min), 5 with moderate (CLCR 26 to 49 ml/min) and 6 with severe (CLCR 5 to 25 ml/min) renal impairment.

OUTCOME MEASURES

Noncompartmental pharmacokinetic parameters were determined for each study participant.

RESULTS

At steady state, in the severe renal disease group, cilostazol and OPC-13015 peak concentrations (Cmax) were 29 and 41% lower and the areas under the concentration-time curve over the dosage interval (AUC tau) 39 and 47% lower than in the healthy volunteers. Cmax and AUC tau of OPC-13213 were significantly higher, 173 and 209%, respectively, than those in the healthy volunteers. The accumulation ratios were not significantly different between the various renal function groups for cilostazol and its metabolites. The estimated pharmacological activity of cilostazol and its metabolites was similar between the normal volunteers and those with severe renal impairment.

CONCLUSIONS

A dosage reduction in renally impaired patients is not supported by the pharmacokinetics of cilostazol and its metabolites in this patient group.

Effect of multiple cilostazol doses on single dose lovastatin pharmacokinetics in healthy volunteers

OBJECTIVE

To assess the effects of cilostazol on lovastatin pharmacokinetics.

DESIGN

This was a single-centre, open-label, multiple dose, sequential treatment study. Participants received single oral doses of lovastatin 80 mg on days 1, 7 and 9, as well as oral cilostazol 100 mg twice daily on days 2 to 8, followed by a single oral 150 mg cilostazol dose on day 9.

STUDY PARTICIPANTS

15 healthy, nonsmoking male or female volunteers (aged 18 to 60 years) were enrolled, and 12 completed the study.

MAIN OUTCOME MEASURES

Pharmacokinetic parameters were calculated using plasma concentrations of lovastatin and its beta-hydroxy metabolite and of cilostazol and its metabolites. Differences in the pharmacokinetics of each drug when given alone or in combination were assessed by analysis of variance.

RESULTS

The maximum observed plasma concentration (Cmax) of lovastatin or its metabolite did not differ significantly when lovastatin was given alone and when it was given with 100 mg of cilostazol. The mean ratios of the area under the plasma concentration-time curve from zero to the time of the last measurable concentration (AUCt) for lovastatin coadministered with 100 mg of cilostazol to that with lovastatin given alone were 1.6 for lovastatin and 1.7 for its metabolite. With 150 mg of cilostazol, lovastatin Cmax did not change, whereas Cmax of the metabolite increased 2.2-fold. The mean AUCt ratios for lovastatin given with 150 mg cilostazol/lovastatin given alone were 1.6 and 2.0 for lovastatin and its metabolite, respectively. All increases in lovastatin and metabolite AUC were statistically significant, except for the 1.6-fold increase in lovastatin AUC with 150 mg of cilostazol. Maximum steady-state plasma drug concentration (Cssmax) and AUC during a dosage interval (AUC tau) for cilostazol 100 mg twice daily decreased 14 and 15%, respectively, upon lovastatin coadministration.

CONCLUSIONS

Lovastatin and metabolite exposure is increased only by up to 2-fold when cilostazol is coadministered, which is considerably less than that observed for potent CYP3A inhibitors such as itraconazole and grapefruit juice. Absorption of cilostazol decreased approximately 15% when it was given with lovastatin. No dosage adjustments are necessary for cilostazol when coadministered with lovastatin, whereas lovastatin dose reductions may be needed when the 2 drugs are given together.

High-performance liquid chromatographic method for the determination of salicylic acid and its metabolites in urine by direct injection

A direct injection method has been developed for the determination of salicylic acid and its metabolites in urine. Urine samples are treated with hydroxylamine to convert salicyl acyl glucuronide to salicylhydroxamic acid, which can be accurately quantitated by direct injection into a high-performance liquid chromatographic system along with salicylic acid, gentisic acid and salicyluric acid. Salicyl phenolic glucuronide is quantitated by difference after hydrochloric acid hydrolysis at 65 degrees C with no loss of salicylic acid by sublimation or hydrolytic loss of salicyluric acid. This method has been applied to urine samples from human subjects and the results are discussed.