Evaluation of herb-drug interaction of ambrisentan with shikonin based on UPLC-MS/MS

CONTEXT

Ambrisentan is an oral endothelin-receptor antagonist (ERA). However, there is no report on the interaction between ambrisentan and shikonin.

OBJECTIVE

To investigate the effect of shikonin on ambrisentan metabolism in vivo and in vitro.

MATERIALS AND METHODS

This study developed an ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method for simultaneous determination of ambrisentan and (S)-4-hydroxymethyl ambrisentan in rat plasma. Twelve male Sprague-Dawley (SD) rats were divided into two groups (n = 6): the control group and shikonin (20 mg/kg) group. The pharmacokinetics of ambrisentan (2.5 mg/kg) were investigated after 30 min. Additionally, human and rat liver microsomes were used to investigate the herb-drug interaction.

RESULTS

The UPLC-MS/MS method was shown to be accurate, precise and reliable, and was successfully applied to the herb-drug interaction study of ambrisentan with shikonin. When co-administrated with 20 mg/kg shikonin, the C_max and AUC_(0-∞) of ambrisentan were significantly increased by 44.96 and 16.65%, respectively (p < 0.05). In addition, there were modest decreases in (S)-4-hydroxymethyl ambrisentan C_max and AUC_(0-∞) in the presence of shikonin (p < 0.05), which indicated that these results were in accordance with the inhibition of shikonin on ambrisentan metabolism. Moreover, enzyme kinetic study indicated that shikonin had an inhibitory effect on human and rat microsomes where the IC₅₀ values of shikonin were 5.865 and 6.358 μM, respectively.

CONCLUSIONS

Our study indicated that shikonin could inhibit ambrisentan metabolism. Further studies need to be carried out to verify whether similar interaction truly apply in humans and whether this interaction has clinical significance.

Open-label, single-center, phase I trial to investigate the mass balance and absolute bioavailability of the highly selective oral MET inhibitor tepotinib in healthy volunteers

Tepotinib (MSC2156119J) is an oral, potent, highly selective MET inhibitor. This open-label, phase I study in healthy volunteers (EudraCT 2013-003226-86) investigated its mass balance (part A) and absolute bioavailability (part B). In part A, six participants received tepotinib orally (498 mg spiked with 2.67 MBq [¹⁴C]-tepotinib). Blood, plasma, urine, and feces were collected up to day 25 or until excretion of radioactivity was <1% of the administered dose. In part B, six participants received 500 mg tepotinib orally as a film-coated tablet, followed by an intravenous [¹⁴C]-tepotinib tracer dose (53–54 kBq) 4 h later. Blood samples were collected until day 14. In part A, a median of 92.5% (range, 87.1–96.9%) of the [¹⁴C]-tepotinib dose was recovered in excreta. Radioactivity was mainly excreted via feces (median, 78.7%; range, 69.4–82.5%). Urinary excretion was a minor route of elimination (median, 14.4% [8.8–17.7%]). Parent compound was the main constituent in excreta (45% [feces] and 7% [urine] of the radioactive dose). M506 was the only major metabolite. In part B, absolute bioavailability was 72% (range, 62–81%) after oral administration of 500 mg tablets (the dose and formulation used in phase II trials). In conclusion, tepotinib and its metabolites are mainly excreted via feces; parent drug is the major eliminated constituent. Oral bioavailability of tepotinib is high, supporting the use of the current tablet formulation in clinical trials. Tepotinib was well tolerated in this study with healthy volunteers.

A randomized, placebo-controlled, phase 1 study to evaluate the effects of TAK-063 on ketamine-induced changes in fMRI BOLD signal in healthy subjects

RATIONALE

Phosphodiesterase 10A inhibitor TAK-063 has shown effects that suggest efficacy in schizophrenia treatment.

OBJECTIVE

This randomized, double-blind, placebo-controlled, incomplete-crossover study investigated effects of single oral administration of TAK-063 on ketamine-induced changes in blood oxygen level-dependent (BOLD) signal in healthy males.

METHODS

Healthy men aged 18 to 45 years with normal magnetic resonance imaging (MRI) scans and electroencephalogram measurements at screening were eligible. Each subject was randomized to one of nine treatment schedules: all subjects received placebo and two of three doses of TAK-063 followed by ketamine. The primary endpoint was ketamine-induced brain activity in select regions of the brain during resting state. Secondary endpoints included pharmacokinetic parameters of TAK-063, proportion of subjects with treatment-emergent adverse events (AEs), and percentage of subjects meeting criteria for abnormal safety laboratory tests and vital sign measurements.

RESULTS

The study comprised 27 subjects. Prior to ketamine infusion, TAK-063 exerted region-specific effects on resting state functional MRI (fMRI) BOLD signal. After ketamine administration, TAK-063 reduced the Cohen's effect size for resting-state fMRI BOLD signal in key brain regions examined, and exerted similar effects on BOLD signal during the working memory task across all doses. TAK-063 was safe and well tolerated.

CONCLUSIONS

Our results are consistent with non-clinical studies of ketamine and TAK-063 and clinical studies of ketamine and risperidone. It is unknown whether these data are predictive of potential antipsychotic efficacy, and further analyses are required.

Validated LC-MS/MS Method for the Quantification of Ponatinib in Plasma: Application to Metabolic Stability

In the current work, a rapid, specific, sensitive and validated liquid chromatography tandem mass-spectrometric method was developed for the quantification of ponatinib (PNT) in human plasma and rat liver microsomes (RLMs) with its application to metabolic stability. Chromatographic separation of PNT and vandetanib (IS) were accomplished on Agilent eclipse plus C18 analytical column (50 mm × 2.1 mm, 1.8 μm particle size) maintained at 21±2°C. Flow rate was 0.25 mLmin^-1 with run time of 4 min. Mobile phase consisted of solvent A (10 mM ammonium formate, pH adjusted to 4.1 with formic acid) and solvent B (acetonitrile). Ions were generated by electrospray (ESI) and multiple reaction monitoring (MRM) was used as basis for quantification. The results revealed a linear calibration curve in the range of 5–400 ngmL^-1 (r² ≥ 0.9998) with lower limit of quantification (LOQ) and lower limit of detection (LOD) of 4.66 and 1.53 ngmL^-1 in plasma, 4.19 and 1.38 ngmL^-1 in RLMs. The intra- and inter-day precision and accuracy in plasma ranged from1.06 to 2.54% and -1.48 to -0.17, respectively. Whereas in RLMs ranged from 0.97 to 2.31% and -1.65 to -0.3%. The developed procedure was applied for quantification of PNT in human plasma and RLMs for study metabolic stability of PNT. PNT disappeared rapidly in the 1st 10 minutes of RLM incubation and the disappearance plateaued out for the rest of the incubation. In vitro half-life (t_1/2) was 6.26 min and intrinsic clearance (CL_in) was 15.182± 0.477.

Selective Brain-Targeted Antagonism of p38 MAPKα Reduces Hippocampal IL-1β Levels and Improves Morris Water Maze Performance in Aged Rats

Background: P38 mitogen activated protein kinase (MAPK) α modulates microglia-mediated inflammatory responses and a number of neuronal physiological processes.

Objective: To evaluate pre-clinically the pharmacological effects in the brain of p38 MAPKα inhibition with a brain-penetrant specific chemical antagonist.

Methods: VX-745, a blood-brain barrier penetrant, highly selective p38 MAPKα inhibitor, and clinical stage investigational drug, was utilized. Initially, a pilot study in 26-month-old Tg2576 mice was conducted. Subsequently, a definitive dose-response study was conducted in aged (20–22 months) rats with identified cognitive deficits; n = 15 per group: vehicle, 0.5, 1.5, and 4.5 mg/kg VX-745 by oral gavage twice daily for 3 weeks. Assessments in aged rats included IL-1β, PSD-95, TNFα protein levels in hippocampus; and Morris water maze (MWM) test for cognitive performance.

Results: Drug effect could not be assessed in Tg2576 mice, as little inflammation was evident. In cognitively-impaired aged rats, VX-745 led to significantly improved performance in the MWM and significant reduction in hippocampal IL-1β protein levels, though the effects were dissociated as the MWM effect was evident at a lower dose level than that required to lower IL-1β. Drug concentration-effect relationships and predicted human doses were determined.

Conclusions: Selective inhibition of p38 MAPKα with VX-745 in aged rats reduces hippocampal IL-1β levels and improves performance in the MWM. As the two effects occur at different dose levels, the behavioral effect appears to be via a mechanism that is independent of reducing cytokine production. The predicted human doses should minimize risks of systemic toxicity.

Characterization of PCS1055, a novel muscarinic M4 receptor antagonist

Identification of synthetic ligands selective for muscarinic receptor subtypes has been challenging due to the high sequence identity and structural homology among the five muscarinic acetylcholine receptors. Here, we report the pharmacological characterization of PCS1055, a novel muscarinic M4 receptor antagonist. PCS1055 inhibited radioligand [(3)H]-NMS binding to the M4 receptor with a Ki=6.5nM. Though the potency of PCS1055 is lower than that of pan-muscarinic antagonist atropine, it has better subtype selectivity over previously reported M4-selective reagents such as the muscarinic-peptide toxins (Karlsson et al., 1994; Santiago and Potter, 2001a) at the M1 subtype, and benzoxazine ligand PD102807 at the M3-subtype (Bohme et al., 2002). A detailed head-to-head comparison study using [(3)H]-NMS competitive binding assays characterizes the selectivity profiles of PCS1055 to that of other potent muscarinic-antagonist compounds PD102807, tropicamide, AF-DX-384, pirenzapine, and atropine. In addition to binding studies, the subtype specificity of PCS1055 is also demonstrated by functional receptor activation as readout by GTP-γ-[(35)S] binding. These GTP-γ-[(35)S] binding studies showed that PCS1055 exhibited 255-, 69.1-, 342- and >1000-fold greater inhibition of Oxo-M activity at the M4 versus the M1-, M2(-), M3-or M5 receptor subtypes, respectively. Schild analyses indicates that PCS1055 acts as a competitive antagonist to muscarinic M4 receptor, and confirms the affinity of the ligand to be low nanomolar, Kb=5.72nM. Therefore, PCS1055 represents a new M4-preferring antagonist that may be useful in elucidating the roles of M4 receptor signaling.

An efficacy and mechanism evaluation study of Levosimendan for the Prevention of Acute oRgan Dysfunction in Sepsis (LeoPARDS): protocol for a randomized controlled trial

BACKGROUND

Organ dysfunction consequent to infection ('severe sepsis') is the leading cause of admission to an intensive care unit (ICU). In both animal models and early clinical studies the calcium channel sensitizer levosimendan has been demonstrated to have potentially beneficial effects on organ function. The aims of the Levosimendan for the Prevention of Acute oRgan Dysfunction in Sepsis (LeoPARDS) trial are to identify whether a 24-hour infusion of levosimendan will improve organ dysfunction in adults who have septic shock and to establish the safety profile of levosimendan in this group of patients.

METHODS/DESIGN

This is a multicenter, randomized, double-blind, parallel group, placebo-controlled trial. Adults fulfilling the criteria for systemic inflammatory response syndrome due to infection, and requiring vasopressor therapy, will be eligible for inclusion in the trial. Within 24 hours of meeting these inclusion criteria, patients will be randomized in a 1:1 ratio stratified by the ICU to receive either levosimendan (0.05 to 0.2 μg.kg⁻¹.min⁻¹ or placebo for 24 hours in addition to standard care. The primary outcome measure is the mean Sequential Organ Failure Assessment (SOFA) score while in the ICU. Secondary outcomes include: central venous oxygen saturations and cardiac output; incidence and severity of renal failure using the Acute Kidney Injury Network criteria; duration of renal replacement therapy; serum bilirubin; time to liberation from mechanical ventilation; 28-day, hospital, 3 and 6 month survival; ICU and hospital length-of-stay; and days free from catecholamine therapy. Blood and urine samples will be collected on the day of inclusion, at 24 hours, and on days 4 and 6 post-inclusion for investigation of the mechanisms by which levosimendan might improve organ function. Eighty patients will have additional blood samples taken to measure levels of levosimendan and its active metabolites OR-1896 and OR-1855. A total of 516 patients will be recruited from approximately 25 ICUs in the United Kingdom.

DISCUSSION

This trial will test the efficacy of levosimendan to reduce acute organ dysfunction in adult patients who have septic shock and evaluate its biological mechanisms of action.

TRIAL REGISTRATION

Current controlled trials ISRCTN12776039 (19 September 2013).

Analysis of the potential effect of ponatinib on the QTc interval in patients with refractory hematological malignancies

Purpose

Cardiac dysfunction, particularly QT interval prolongation, has been observed with tyrosine kinase inhibitors approved to treat chronic myeloid leukemia. This study examines the effects of ponatinib on cardiac repolarization in patients with refractory hematological malignancies enrolled in a phase 1 trial.

Methods

Electrocardiograms (ECGs) were collected at 3 dose levels (30, 45, and 60 mg) at 6 time points. Electrocardiographic parameters, including QTc interval, were measured, and 11 morphological analyses were conducted. Central tendency analyses of ECG parameters were performed using time-point and time-averaged approaches. All patients with at least 2 baseline ECGs and 1 on-treatment ECG were included in the analyses. Patients with paired ECGs and plasma samples were included in the pharmacokinetic/pharmacodynamic analysis to examine the relationship between ponatinib plasma concentration and change from baseline in QT intervals.

Results

Thirty-nine patients at the 30-, 45-, and 60-mg dose levels were included in the central tendency and morphological analyses. There was no significant effect on cardiac repolarization, as evidenced by non-clinically significant mean QTcF changes from baseline of −10.9, −3.6, and −5.0 ms for the 30-, 45-, and 60-mg dose levels, respectively. The morphological analysis revealed 2 patients with atrial fibrillation and 2 with T wave inversion. Seventy-five patients were included in the pharmacokinetic/pharmacodynamic analysis across all dose levels. The slope of the relationship for QTcF versus plasma ponatinib concentration was not positive (−0.0171), indicating no exposure–effect relationship.

Conclusions

Ponatinib is associated with a low risk of QTc prolongation in patients with refractory hematological malignancies.

Acceptable plasma concentrations of raltegravir and etravirine when administered by gastrostomy tube in a patient with advanced multidrug-resistant human immunodeficiency virus infection

STUDY OBJECTIVE

To determine whether the absorption of four antiretroviral agents-raltegravir, etravirine, emtricitabine, and tenofovir-is compromised when administered by gastrostomy tube.

DESIGN

Pharmacokinetic analysis.

SETTING

University medical center.

PATIENT

A 52-year-old African-American man coinfected with advanced multidrug-resistant human immunodeficiency virus (HIV) and chronic hepatitis B, who was receiving treatment with raltegravir, etravirine, emtricitabine, and tenofovir, and developed ulcerative esophagitis with perforation, requiring a gastrostomy tube.

MEASUREMENTS AND MAIN RESULTS

Due to the patient's esophageal perforations, all nutrition and drug therapy had to be provided by gastrostomy tube. As his antiretroviral regimen of raltegravir, etravirine, and emtricitabine-tenofovir was not available in liquid or powder formulations, the oral tablets were crushed or dispersed and mixed with water, then administered by gastrostomy tube. To ensure that the absorption of the drugs was sufficient for antiretroviral response, plasma samples were collected at 2 hours and 12 hours after dosing, and drug concentrations were quantitated by using validated assays. The 2- and 12-hour postdose plasma concentrations were 1220 and 446 ng/ml for raltegravir, 212 and 274 ng/ml for etravirine, 1148 and 164 ng/ml for emtricitabine, and 320 and 94 ng/ml for tenofovir, respectively. The patient's plasma concentrations were then compared with those in published pharmacokinetic studies of oral regimens administered to HIV-infected persons and healthy volunteers. Overall, the plasma concentrations of the antiretrovirals administered by gastrostomy tube were similar to published values. No drug toxicities were observed in this patient.

CONCLUSION

These pharmacokinetic data suggest that absorption of raltegravir, etravirine, emtricitabine, and tenofovir was not compromised when the drugs were administered by gastrostomy tube. These findings provide a basis for further investigation of the pharmacokinetics, safety, tolerance, and antiretroviral response to raltegravir, etravirine, and emtricitabine-tenofovir when the oral route of administration is not possible.

A novel LC-ESI-MS method for the simultaneous determination of etravirine, darunavir and ritonavir in human blood plasma

The new potent combination of antiretrovirals etravirine, darunavir, and ritonavir requires a new bioanalytical method for clinical pharmacology investigations and potential therapeutic drug monitoring. The development and validation of a novel LC-MS method for the simultaneous quantification of the most recently FDA-approved protease inhibitor and non-nucleoside reverse transcriptase inhibitor is described. This novel method was developed and validated using a sub-2 microm particle column, and provides excellent chromatographic separation and peak shape for all three analytes and internal standard. The method was validated over the range of 0.002-2.0 microg/mL. Intra- and inter-day accuracy of all analytes ranged from 88 to 106%, and intra- and inter-day precision was <7%. Dilution of samples 2-, 5-, and 10-fold maintained accuracy and precision, using a sample volume as low as 10 microL. Finally, the applicability of the method was investigated with clinical samples and external quality assurance proficiency testing samples.

[Determination of levosimendan and its main metabolites in human plasma with HPLC-MS/MS method]

This paper is aimed to develop rapid, sensitive and convenient HPLC-MS/MS methods for the quantification of levosimendan and its metabolites OR-1855 and OR-1896 in human plasma. According to the different natures of the compounds, two sets of liquid chromatography and ionization modes were used for determination the concentration of levosimendan and its metabolites OR-1855 and OR-1896 in human plasma, separately. Following protein precipitation with methanol, the levosimendan and internal standard (rosuvastatin) were separated on a Capcell MG III C18 column (35 mm x 2.0 mm ID, 3 microm) with the mobile phase consisted of methanol-15 mmol x L(-1) ammonium acetate-formic acid (55: 45: 0.02, v/v/v). A tandem mass spectrometer equipped with electrospray ionization source was used as the detector and operated in the negative ion mode. Its metabolites OR-1855, OR-1896 and internal standard doxofylline were extracted from plasma by liquid-liquid extraction with ethyl acetate. Chromatographic separation was performed on a Zorbax Extend C18 column (150 mm x 4.6 mm ID, 5 microm) with the mobile phase consisted of methanol-15 mmol x L(-1) ammonium acetate-formic acid (65 :35 :0.1, v/v/v). A tandem mass spectrometer equipped with electrospray ionization source was used as the detector and operated at the positive ion mode. The linear concentration ranges of the calibration curves for levosimendan and OR-1855 and OR-1896 were 0.10-50.0 ng x mL(-1), 0.20-100 ng x mL(-1), 0.20-100 ng x mL(-1), respectively. The lower limits of quantification of levosimendan and OR-1855 and OR-1896 were 0.10 ng x mL(-1), 0.20 ng x mL(-1), 0.20 ng x mL(-1), respectively. The methods proved to be sensitive, simple and rapid, and suitable for the pharmacokinetic study of levosimendan injection.

Pharmacokinetics of elvitegravir and etravirine following coadministration of ritonavir-boosted elvitegravir and etravirine

BACKGROUND

This crossover, open-label clinical study evaluated the potential for clinically relevant drug interactions between ritonavir-boosted elvitegravir (elvitegravir/r), an HIV integrase inhibitor, and etravirine, a non-nucleoside reverse transcriptase inhibitor.

METHODS

Healthy volunteers were randomized into one of two groups, each with two arms. Group 1 (n = 20) followed a sequence of 10-day dosing of elvitegravir/r (150/100 mg once daily) and elvitegravir/r plus etravirine (200 mg twice daily) or the reverse (n = 10 per sequence). Group 2 (n = 14) followed a sequence of 10-day dosing of etravirine and etravirine plus elvitegravir/r or the reverse (n = 7 per sequence), all under fed conditions. Elvitegravir, ritonavir and etravirine pharmacokinetics were determined on days 10 and 20 using non-compartmental analyses. Lack of pharmacokinetic alteration bounds for 90% confidence intervals (CI) about the geometric mean ratio (GMR; coadministration versus alone) were 70-143% for elvitegravir and ritonavir pharmacokinetics (maximum concentration [C(max)], concentration at the end of the dosing interval [C(tau)] and area under the plasma concentration-time curve [AUC(tau); 0-24 h] and 80-125% for etravirine pharmacokinetics (AUC(tau) 0-12 h).

RESULTS

Of the 34 enrolled participants, 31 completed the study. There were three discontinuations, but none were caused by adverse events (AEs). The most common treatment-emergent AE was headache. Elvitegravir pharmacokinetic GMR was 6-7% higher following elvitegravir/r plus etravirine dosing versus elvitegravir/r. The GMR for etravirine and ritonavir AUC(tau) were 2.4% and 12.3% lower, respectively. Importantly, the 90% CI for elvitegravir and etravirine pharmacokinetics and AUC(tau) and C(max) for ritonavir were within the lack of alteration bounds.

CONCLUSIONS

Elvitegravir/r and etravirine do not undergo clinically relevant drug interactions and can be coadministered without dose adjustment.

A strategy for high-throughput analysis of levosimendan and its metabolites in human plasma samples using sequential negative and positive ionization liquid chromatography/tandem mass spectrometric detection

Levosimendan (Simdax) is an approved drug in approximately 40 countries and currently in phase III clinical studies in the USA and Europe. An accurate, high-throughput and rugged assay is critical to support these clinical trials. Due to the mechanism of drug metabolism, the drug and its active metabolites often have significant differences in their chemical properties. In order to achieve high assay throughput and low sample volumes, a single bioanalytical assay for the drug and its metabolites is preferred. However, this need may prevent the optimization of both high-performance liquid chromatography (HPLC) and mass spectrometric ionization conditions. The chemical properties of levosimendan are significantly different from those of its two active metabolites, OR-1855 and OR-1896. Here, we present a novel strategy for high-throughput analysis of levosimendan and its metabolites. A 96-well liquid/liquid extraction procedure was developed for sample preparation. A single liquid chromatography/tandem mass spectrometry (LC/MS/MS) system with two separate mobile phases, shared backwash solvent and conditioning solvent, was developed to perform sequential LC separation for levosimendan and the metabolites. Levosimendan was eluted by 5 mM ammonium acetate in 33.3% acetonitrile and detected using negative ionization mode MS/MS monitoring. The metabolites were eluted by 5 mM ammonium acetate and 0.2% acetic acid in 20% acetonitrile and detected with positive ionization mode MS/MS monitoring. The method has been demonstrated to have excellent precision and accuracy, with high assay ruggedness during method validation and clinical sample analysis. The linear dynamic ranges were approximately 200-50,000 pg/mL for levosimendan and approximately 500-130,000 pg/mL for both metabolites. The coefficient of determination (r2) for all analytes was greater than 0.9985. The intra-assay %CVs for QC samples were from 0.9% to 2.0% for levosimendan, 0.9% to 3.2% for OR-1855, and 0.4% to 4.9% for OR-1896. The inter-assay %CVs for QC samples were from 1.2% to 1.8% for levosimendan, 1.3% to 2.7% for OR-1855, and 1.4% to 3.4% for OR-1896. The mean % biases for QC samples were from 1.5% to 5.5% for levosimendan, -1.4% to 2.6% for OR-1855, and -0.3% to 4.5% for OR-1896. By using a single extraction approach coupled with sequential LC/MS/MS analysis for levosimendan and its metabolites, the assay maintained high throughput and low sample volume usage.

Pharmacokinetics of darunavir/ritonavir and TMC125 alone and coadministered in HIV-negative volunteers

OBJECTIVE

To evaluate the pharmacokinetics of TMC125 (etravirine) and darunavir (DRV) with low-dose ritonavir (DRV/r).

DESIGN

Open-label, randomized, two-way crossover Phase I trial.

METHODS

Thirty-two HIV-negative volunteers were randomized 1:1 to two panels. All received TMC125 100 mg twice daily for 8 days and, after 14 days washout, DRV/r 600/100 mg twice daily for 16 days. During days 9-16, TMC125 100 or 200 mg twice daily was coadministered (Panel I or II, respectively).

RESULTS

Twenty-three volunteers completed the trial. With DRV/r coadministration, mean exposure (area under the plasma concentration-time curve from 0 to 12 h [AUC12h) to TMC125 given as 100 mg twice daily was decreased by 37%; maximum and minimum plasma concentrations (Cmax and Cmin) were decreased by 32% and 49%, respectively. For TMC125 200 mg twice daily coadministered with DRV/r, AUC12h, Cmax and Cmin of TMC125 were 80%, 81% and 67% greater, respectively, versus TMC125 100 mg twice daily alone. DRV pharmacokinetics were unchanged except a 15% increase in AUC12h when given with TMC125 200 mg twice daily.

CONCLUSIONS

No clinically relevant changes in DRV pharmacokinetics were observed when combined with TMC125; therefore DRV dose adjustment is not required. Coadministration of TMC125 100 mg twice daily with DRV/r decreased TMC125 exposure by 37%. The increase of TMC125 exposure by 80% when given as 200 mg twice daily reflects the higher dose and the interaction with DRV/r. The magnitude of this interaction is comparable to TMC125 interactions with other boosted PIs observed in Phase IIb trials in HIV-1-infected patients. As these trials demonstrated TMC125 efficacy, no dose adjustment of TMC125 is needed when combined with DRV/r.

The Effect of Levosimendan during Long-Term Amiodarone Treatment in Dogs

The haemodynamic and electrophysiological effects of levosimendan were studied in conscious dogs receiving long-term oral amiodarone treatment. Instrumented dogs were administered increasing doses of levosimendan (up to 0.9 microg/kg/min. intravenously) in three successive 30 min. infusions. This schedule was repeated on the 21st day of treatment with oral amiodarone 100 mg/kg/day. The extent of increase in left ventricular systolic pressure (LVSP) and the decrease in left ventricular end-diastolic pressure (LVEDP) seen with levosimendan were similar before and after long-term treatment with amiodarone. The levosimendan-induced increases in isovolumic contraction (+dP/dt) and in left ventricular contractility (dP/dt/P) seen prior to amiodarone administration were augmented during amiodarone treatment, an effect that was statistically significant (P<0.05) at the highest doses of levosimendan. A tendency towards a shortening of the QT interval and a rise in heart rate was observed for levosimendan alone but they did not exceed the physiological range when the drug was given in combination with amiodarone. QTc value was unaffected by levosimendan either alone or with amiodarone. These effects were apparent in animals with therapeutically meaningful plasma levels of levosimendan, amiodarone and desethylamiodarone levels. The results of this study show that the improvement in ventricular contractile performance usually associated with administration of levosimendan was somewhat enhanced by chronic oral treatment with amiodarone. It seems reasonable to infer that the inotropic potency and electrophysiological safety of parenteral levosimendan will be maintained in patients with heart failure during long-term treatment with oral amiodarone.

Level A in vitro-in vivo Correlation (IVIVC) Model with Bayesian Approach to Formulation Series

In vitro-in vivo correlation (IVIVC) models for formulation series are useful in drug development, but the current models are limited by their inability to include data variability in the predictions. Our goal was to develop a level A IVIVC model that provides predictions with probabilities. The Bayesian approach was used to describe uncertainty related to the model and the data. Three bioavailability studies of levosimendan were used to develop IVIVC model. Dissolution was tested at pH 5.8 with basket. The IVIVC model with Bayesian approach consisted of prior and observed data. All observed data were fitted to the one-compartment model together with prior data. Probability distributions of pharmacokinetic parameters and concentration time profiles were obtained. To test the external predictability of IVIVC model, only dissolution data of formulations E and F were used. The external predictability was good. The possibility to utilize all observed data when constructing IVIVC model, can be considered as a major strength of Bayesian approach. For levosimendan capsule data traditional IVIVC model was not predictable. The usefulness of IVIVC model with Bayesian approach was shown with our data, but the same approach can be used more widely for formulation optimization and for dissolution based biowaivers.

The in vivo metabolism of 3-oxo-5-benzylidene-6-methyl-(4H)-2-(benzoylmethyl)pyridazine in rats

The purpose of the study was to investigate the in vivo metabolic pathway of 3-oxo-5-benzylidene-6-methyl-(4H)-2-(benzoylmethyl)pyridazine (substrate) in rats. Firstly its potential metabolites, i.e. N-dealkylation, ring scission of pyridazine and aromatic hydroxylation products, were synthesized and then the substrate was given orally (100 mg/kg) to male or female Wistar rats at a dose of 100 mg/kg to body weight. Blood samples were collected at 0, 1, 2, 4, 6 and 8 hours after administration of substrate and blood was centrifuged to obtain serum. The substrate and its potential metabolites were separated using a gradient HPLC method on a reverse phase system. This study revealed that 3-oxo-5-benzylidene-6-methyl-(4H)-2-(benzoylmethyl)pyridazine was not metabolized to the proposed metabolites and was present unchanged in the serum.

Imidazo[1,2-b]pyridazines: a potent and selective class of cyclin-dependent kinase inhibitors

Modification of imidazo[1,2-a]pyridine CDK inhibitors lead to identification of less lipophilic imidazo[1,2-b]pyridazine series of CDK inhibitors. Although several equivalent compounds from these two series have similar structure and show similar CDK activity, the SAR of the two series differs significantly. Protein inhibitor structure determination has confirmed differences in binding mode and given some understanding of these differences in SAR. Potent and selective imidazo[1,2-b]pyridazine inhibitors of CDK2 have been identified, which show >1 microM plasma levels following a 2mg/kg oral dose to mice.

ABT-963 [2-(3,4-Difluoro-phenyl)-4-(3-hydroxy-3-methyl-butoxy)-5-(4-methanesulfonyl-phenyl)-2H-pyridazin-3-one], A Highly Potent and Selective Disubstituted Pyridazinone Cyclooxgenase-2 Inhibitor

Nonsteriodal anti-inflammatory drugs (NSAIDs) are efficacious for the treatment of pain associated with inflammatory disease. Clinical experience with marketed selective cyclooxygenase-2 (COX-2) inhibitors (celecoxib, rofecoxib, and valdecoxib) has confirmed the utility of these agents in the treatment of inflammatory pain with an improved gastrointestinal safety profile relative to NSAID comparators. These COX-2 inhibitors belong to the same structural class. Each contains a core heterocyclic ring with two appropriately substituted phenyl rings appended to adjacent atoms. Here, we report the identification of vicinally disubstituted pyridazinones as potent and selective COX-2 inhibitors. The lead compound in the series, ABT-963 [2-(3,4-difluoro-phenyl)-4-(3-hydroxy-3-methyl-butoxy)-5-(4-methanesulfonyl-phenyl)-2H-pyridazin-3-one], has excellent selectivity (ratio of 276, COX-2/COX-1) in human whole blood, improved aqueous solubility compared with celecoxib and rofecoxib, high oral anti-inflammatory potency in vivo, and gastric safety in the animal studies. After oral administration, ABT-963 reduced prostaglandin E2 production in the rat carrageenan air pouch model (ED50 of 0.4 mg/kg) and reduced the edema in the carrageenan induced paw edema model with an ED30 of 1.9 mg/kg. ABT-963 dose dependently reduced nociception in the carrageenan hyperalgesia model (ED50 of 3.1 mg/kg). After 14 days of dosing in the adjuvant arthritis model, ABT-963 had an ED(50) of 1.0 mg/kg in reducing the swelling of the hind paws. Magnetic resonance imaging examination of the diseased paws in the adjuvant model showed that ABT-963 significantly reduced bone loss and soft tissue destruction. ABT-963 is a highly selective COX-2 inhibitor that may have utility in the treatment of the pain and inflammation associated with arthritis.

Cardiotonic agent SCH00013 prolongs survival of cardiomyopathic hamsters

The authors examined the effects of long-term treatment with SCH00013, a novel cardiotonic agent with calcium-sensitizing action, on survival of hereditary cardiomyopathic BIO 14.6 hamsters. Sixty-nine male hamsters at 223 days of age were divided into untreated, SCH00013-low (approximately 1 mg/kg/d), and SCH00013-high (approximately 10 mg/kg/d) groups. Survival curves were constructed in the three groups. The first deaths in the untreated, SCH00013-low, and SCH00013-high groups were found at 263, 290, and 314 days of age, respectively. A 50% mortality rate was observed at 392 days in the untreated group, 396 days in the SCH00013-low group, and 445 days in SCH00013-high group. The survival time distribution of the SCH00013-high group was significantly different from that of the untreated group (P < 0.005). However, histomorphometric examinations revealed that the degree of progression of calcification and fibrosis in the ventricular wall of the BIO 14.6 hamsters was not different between the untreated and SCH00013-treated groups. Plasma concentration of this agent was 2 microM at the end of the second week of continuous administration via drinking water in SCH00013-high group. Thus, SCH00013 was beneficial for the survival of cardiomyopathic hamsters, suggesting that this agent is a possible candidate for the treatment of chronic heart failure.

Pharmacodynamic Interactions of Levosimendan and Felodipine in Patients with Coronary Heart Disease

OBJECTIVE

The aim was to study the pharmacodynamic interactions and safety of the co-administration of the calcium sensitizer levosimendan and the calcium antagonist felodipine in patients with coronary heart disease (CHD) and with normal ejection fraction (EF).

METHODS

The study was a randomized, double blind, placebo-controlled, crossover study in 24 male patients with Canadian Cardiovascular Society (CCS) class II CHD, consisting of four treatment periods, each period lasting for 7-10 days. In the first period the patients received either oral levosimendan (LS) (0.5 mg) or placebo (PL) four times daily and were then crossed over to the other therapy for the second and third period. After the third period the patients were changed back to the therapy administered in the first period. Open label felodipine (FD), 5 mg once daily, was co-administered on the third and fourth treatment period. Differences between the four treatments (LS, PL, FD and LS + FD) in systolic time intervals, exercise capacity, heart rate, blood pressure and 24-hour continuous electrocardiography (Holter) were assessed.

RESULTS

The differences between treatments regarding heart rate corrected electromechanical systole (QS2i), pre-ejection period (PEP) and heart rate corrected left ventricular ejection time (LVETi) were significant (p < 0.001, p < 0.001 and p = 0.004, respectively). Levosimendan shortened QS2i by 10 ms (95% CI [-15, -4]), PEP by 6 ms (95% CI [-10, -3]) and LVETi by 7 ms (95% CI [-13, -2]) compared with placebo, indicating a moderate positive inotropic effect. The results were similar, when levosimendan was administered concomitantly with felodipine. Levosimendan did not significantly change systolic blood pressure and no potentiation of response was seen with concomitant administration with felodipine. The increase in heart rate after levosimendan and its combination with felodipine was equal (6-7 bpm). There was no difference in mean cumulative exercise time between the treatments. The combination of levosimendan and felodipine was well tolerated.

CONCLUSION

No clinically significant pharmacodynamic interactions between levosimendan and felodipine were seen. Levosimendan did not aggravate myocardial ischemia. Levosimendan can safely be administered to patients with CHD together with a dihydropyridine calcium antagonist.

Population pharmacokinetics of levosimendan in patients with congestive heart failure

AIMS

The aim of this study was to characterize the population pharmacokinetics of levosimendan in patients with heart failure (NYHA grades III and IV) and its relationship to demographic factors, disease severity and concomitant use of digoxin and beta-blocking agents.

METHODS

Data from two efficacy studies with levosimendan administered by intravenous infusion were combined (190 patients in total). The data were analysed using a nonlinear mixed-effects modelling approach as implemented in the NONMEM program. The model development was done in three sequential steps. First the best structural model was determined (e.g. a one-, two- or three-compartment pharmacokinetic model). This was followed by the identification and incorporation of important covariates into the model. Lastly the stochastic part of the model was refined.

RESULTS

A two-compartment model best described levosimendan pharmacokinetics. Clearance and the central volume of distribution were found to increase linearly with bodyweight. No other covariates, including concomitant use of digoxin and beta-blocking agents, influenced the pharmacokinetics. In the final model, a 76-kg patient was estimated to have a clearance +/- s.e. of 13.3 +/- 0.4 l h-1 and a central volume of distribution of 16.8 +/- 0.79 l. The interindividual variability was estimated to be 39% and 60% for clearance and central volume of distribution, respectively. Weight changed clearance by 1.5% [95% confidence interval (CI) 0.9%, 2.1%] and the central volume of distribution by 0.9% (95% CI 0.5%, 1.3%) per kg.

CONCLUSIONS

The population pharmacokinetics parameters of levosimendan in this patient group were comparable to those obtained by traditional methods in healthy volunteers and patients with mild heart failure. Bodyweight influenced the clearance and the central volume of distribution, which in practice is accounted for by weight adjusting doses. None of the other covariates, including digoxin and beta-blocking agents, significantly influenced the pharmacokinetics of levosimendan.

Sustained hemodynamic effects of intravenous levosimendan

BACKGROUND

The short-term infusion of levosimendan (Levo) improves hemodynamic function in patients with decompensated heart failure. The metabolites of Levo have a prolonged half-life, and one is hemodynamically active. The goal of this study was to determine whether the hemodynamic effects of Levo are sustained during a long-term infusion and beyond the discontinuation of drug infusion.

METHODS AND RESULTS

Patients with decompensated heart failure received escalating infusion rates of intravenous Levo (n=98) or placebo (n=48) for 6 hours. At the end of 6 hours, 85 of the Levo-treated patients were continued on open-label drug for a total of 24 hours, at which time they were randomized 1:1 to an additional 24 hours of Levo (n=43) or placebo (n=42). The hemodynamic effects observed at 24 hours were maintained at 48 hours in both the continuation and withdrawal groups and did not differ between groups. Although the plasma concentration of Levo decreased rapidly in the withdrawal group, concentrations of the active metabolite OR-1896 were similar in the continuation and withdrawal groups at 24 hours and increased further (3.5-fold to 4-fold) and to a similar extent in both groups at 48 hours.

CONCLUSIONS

The hemodynamic effects of Levo were maintained during a 48-hour continuous infusion and for at least 24 hours after discontinuation of a 24-hour infusion. The active metabolite OR-1896 increased for at least 24 hours after cessation of drug infusion and may account for the prolonged hemodynamic effects of Levo.

Pharmacokinetics of levosimendan and its metabolites during and after a 24-hour continuous infusion in patients with severe heart failure

OBJECTIVE

Levosimendan is a new calcium sensitizer with additional vasodilatory properties developed for the short-term intravenous treatment of congestive heart failure. The aims of the present study were to determine the pharmacokinetics and hemodynamic effects of levosimendan and its metabolites during and after a 24-hour levosimendan infusion.

METHODS

The study was an open-label, non-randomized, phase II study in 2 centers. Twelve patients with NYHA III-IV heart failure received 0.2 microg/kg/min continuous infusion of levosimendan for 24 hours. Blood samples for the determination of plasma concentrations of the parent drug and the metabolites were drawn repeatedly during the infusion and the 2-week follow-up period. Heart rate from Holter recordings and blood pressure were measured.

RESULTS

The elimination half-life of levosimendan was 1.3 hours and that of the metabolites 75-78 hours. The mean maximum increase in heart rate of 10 bpm (p < 0.005) and the mean maximum decreases in systolic and diastolic blood pressure of 12 mmHg and 8 mmHg (p < 0.05 for both), respectively, were observed during the first day after stopping levosimendan infusion. The hemodynamic effects slowly declined during the follow-up, and after 1 week no statistically significant differences compared with baseline were observed. No increase in ventricular arrhythmias was seen.

CONCLUSION

A 24-hour infusion of levosimendan induces hemodynamic effects lasting several days after stopping the infusion. The prolongation of the effects beyond the infusion period is most likely due to an active metabolite with a long half-life.

An analysis of responses to levosimendan in the pulmonary vascular bed of the cat

Calcium-sensitizing drugs, such as levosimendan, are a novel class of drug therapy for heart failure. We investigated the hypothesis that levosimendan is a pulmonary vasodepressor mediated through inhibition of phosphodiesterase, adenosine triphosphate (ATP)-dependent potassium channels, or both. We investigated responses to the calcium sensitizer levosimendan in the pulmonary vascular bed of the cat under conditions of controlled pulmonary blood flow and constant left atrial pressure when lobar arterial pressure was increased to a high steady level with the thromboxane A(2) analog U-46619. Under increased-tone conditions, levosimendan caused dose-related decreases in lobar arterial pressure without altering systemic arterial and left atrial pressure. Responses to levosimendan were significantly attenuated, although not completely, after the administration of U-37883A, a vascular selective nonsulfonylurea ATP-sensitive K(+)-channel-blocking drug. Responses to levosimendan were not significantly different after the administration of the nitric oxide synthase inhibitor L-N(5)-(1-iminoethyl)-ornithine or the cyclooxygenase inhibitor sodium meclofenamate or when lung ventilation was interrupted. These data show that levosimendan has significant vasodilator activity in the pulmonary vascular bed of the cat. They also suggest that pulmonary vasodilator responses to levosimendan are partially dependent on activation of ATP-sensitive K(+) channels and independent of the synthesis of nitric oxide, activation of cyclooxygenase enzyme, or changes in bronchomotor tone in the pulmonary vascular bed of the cat.

IMPLICATIONS

Calcium-sensitizing drugs, such as levosimendan, are a novel class of drug therapy for heart-failure treatment. The lung circulation affects both right- and left-sided heart failure. Levosimendan decreased lobar arterial pressure via a partial K(+)(ATP) (potassium channel sensitive to intracellular adenosine triphosphate levels)-dependent mechanism. These data suggest that, in addition to calcium-sensitizing activity, levosimendan decreases pulmonary resistance, which may also aid in the treatment of heart failure.

Determination of amezinium in plasma by RP HPLC and its application to bioequivalence studies

A modified method is described for the determination of 4-amino-6-methoxy-l-phenylpyridazinium methyl sulfate (amezinium metisulfate) in plasma and in the dosage form. The method involves a sample preparation using SPE and liquid-liquid extraction and subsequent determination by high performance liquid chromatography. Retention time for amezinium was 3.2 min and there was no interference from plasma or amezinium metabolites. The method was applied for the drug determination during comparative studies of two different tablet formulation of amezinium.

Acute effects of a single low oral dose of pimobendan on left ventricular systolic and diastolic function in patients with congestive heart failure

A recent long-term multicenter trial has shown that pimobendan is more effective when administered in low doses. However, no data are available concerning the effect of a low dose of pimobendan on the systolic and diastolic pressure-volume relations in patients with heart failure. Therefore we examined the effects of a single low dose of oral pimobendan, a calcium sensitizer, on systolic and diastolic hemodynamics in patients with cardiomyopathy and congestive heart failure. We measured the left ventricular (LV) pressure-volume relations using a conductance catheter with a micromanometer tip in 10 patients with chronic congestive heart failure resulting from idiopathic cardiomyopathy before and 45 and 90 min after administration of a single oral dose of 2.5 mg of pimobendan. End-systolic elastance was used as an index of LV contractility and was measured during transient occlusion of the inferior vena cava. End-systolic elastance increased significantly by 25% at 45 min (p < 0.05) and by 55% at 90 min (p < 0.01) without an increase in myocardial oxygen consumption. The inotropic effect was accompanied by improved ventriculoarterial coupling. This effect was attenuated in patients with severely impaired myocardial contractility. LV relaxation, assessed by the time constant of isovolumic pressure decay (T(1/2)), was significantly shortened at 90 min (from 47.7 +/- 1.9 to 41.2 +/- 1.7 ms; p < 0.01), although it remained unchanged at 45 min. The diastolic pressure-volume relation showed a leftward and downward shift in all patients. These results indicate that low-dose oral pimobendan had favorable short-term inotropic and lusitropic effects in patients with congestive heart failure caused by idiopathic dilated cardiomyopathy, and may thus be a useful alternative to traditional agents. Further study in a large-scale trial is merited.

Haemodynamic interactions between the novel calcium sensitiser levosimendan and isosorbide-5-mononitrate in healthy subjects

OBJECTIVE

The new calcium sensitiser levosimendan also possesses vasodilatory effects due to potassium-channel opening. The aim of the present study was to assess the possible haemodynamic interactions between levosimendan and isosorbide-5-mononitrate in young healthy men.

METHODS

The study was crossover, placebo controlled, double blind, randomised, and it comprised of four study days with one medication--levosimendan, isosorbide-5-mononitrate, levosimendan plus isosorbide-5-mononitrate or placebo--given on each. Levosimendan was administered i.v. as an initial bolus dose of 12 microg/kg over 10 min, followed by a continuous infusion of 0.2 microg/kg/min for a total time of 2 h. Isosorbide-5-mononitrate (20 mg) was given orally as a single dose. Leg blood flow and venous capacity (venous occlusion plethysmography), cardiac output (impedance cardiography), skin blood flow (laser-Doppler flowmetry), blood pressure and heart rate were recorded at baseline, and 20 min, 1 h, 2 h, 4 h and 6 h after the start of the infusion. An orthostatic test was performed at baseline and at 2 h 15 min. Twelve healthy, male subjects were included. Their mean age was 24 years (range 20-34 years).

RESULTS

Levosimendan increased leg blood flow by 32%, and no additive effect of the combination of levosimendan and isosorbide-5-mononitrate was observed. The effects of levosimendan on heart rate and blood pressure were minimal and in close conformity with previous studies. In general, there were no additive effects of the combination compared with each drug alone at rest. The only additive effect was seen in the orthostatic response. Heart rate increased by 40 beats min(-1) with the combination (95% confidence interval compared with placebo 11-24 beats min(-1)), by 30 beats min(-1) with levosimendan (2-15 beats min(-1)), by 28 beats min(-1) with isosorbide-5-mononitrate (1-15 beats min(-1)), and by 22 beats min(-1) with placebo. Furthermore, three subjects were unable to stand upright for the stipulated time with the combination, and the orthostatic test had to be discontinued prematurely. There were no changes in the conduction intervals in the electrocardiogram on any of the treatments. The combination had no influence on the occurrence of headache compared with isosorbide-5-mononitrate alone.

CONCLUSION

No major additive haemodynamic effects of the combination of levosimendan and isosorbide-5-mononitrate compared with each drug alone could be observed at rest. However, during an orthostatic test, the circulatory response was significantly potentiated with the combination, and three of the subjects were unable to stand upright for the stipulated time.

Site dependent bioavailability and metabolism of levosimendan in dogs

Site specific bioavailability and metabolism of levosimendan was studied in ten dogs by placing intestinal access port catheters in different parts of the gastrointestinal tract. 14C-labelled levosimendan (0.1 mg/kg) was administered intravenously, by gastric tube and directly through catheters that were placed in the duodenum, jejunum and ileum. Plasma samples were collected and radioactivity in the different organs and tissues was measured. The results of the present study showed that bioavailability of levosimendan was high varying from 71 to 86% after extravascular administration. Metabolite OR-1855 concentrations in the plasma were about 3-4 times higher after administration to the ileum compared to the other administration routes. It can be concluded that the bioavailability of levosimendan is not affected by site specific administration. The bacteria or enzymes responsible for the metabolism of levosimendan are located in the lower parts of the gastrointestinal tract.

Integrated pharmacokinetics and pharmacodynamics of the novel calcium sensitizer levosimendan as assessed by systolic time intervals

BACKGROUND

Levosimendan is a new calcium sensitizer, acting calcium-dependently on cardiac troponin C. In the present study pharmacokinetic-pharmacodynamic interrelations of levosimendan were assessed.

SUBJECTS AND METHODS

Ten healthy subjects (22-27 years) were given single doses of 2 mg of levosimendan in 4 different formulations: intravenous (i.v.), conventional tablet (CT), conventional capsule (CC), and slow-release tablet (SR) on different days. Systolic time intervals and impedance cardiography were recorded up to 4 hours post drug. Plasma concentrations of levosimendan and its metabolite OR-1855 were analyzed using HPLC. Hysteresis loops were constructed by connecting the effect-concentration points in time order. In addition, pharmacokinetic-pharmacodynamic modelling was performed with the i.v. data.

RESULTS

The i.v. administration, giving a maximal levosimendan concentration of 180 ng x ml(-1), increased heart rate by 8 beats min(-1) and cardiac output by 18%. It shortened heart rate corrected electromechanical systole QS2i by 23 ms, indicating a fairly strong positive inotropic effect. The conventional oral formulations (giving maximal drug concentrations of about 70-80 ng x ml(-1)) increased heart rate by 4-5 beats min(-1) and cardiac output by 5-8%, while QS2i shortened by 9-13 ms. The SR formulation resulted in low drug concentrations and generally weaker effects than the other formulations. The bioavailability of CT and CC was 83 and 87%, while that of SR was only 31%. QS2i showed counter-clockwise hysteresis after all formulations (p < 0.01). The mean equilibration half-time (ln(2)/k(e0)) after i.v. administration was 9.6 min. Only after SR, OR-1855 was detected in appreciable amounts in plasma, the highest value being 2.2 ng x ml(-1) which occurred 24 hours after drug intake.

CONCLUSION

In conclusion, the pharmacokinetic-dynamic behavior of the inotropy index QS2i indicates an equilibration delay of levosimendan, which most probably reflects the time the drug requires to distribute from plasma to its cardiac site of action. The deviant kinetic-dynamic profile of the oral slow-release formulation suggests a different absorption pattern of levosimendan from this formulation.

High throughput liquid chromatography/mass spectrometry bioanalysis using 96-well disk solid phase extraction plate for the sample preparation

The 96 well solid phase extraction (SPE) operated by robot in the LC/MS/MS bioanalysis offered rapid sample preparation for drugs and metabolites in biological matrices, based on simultaneous extraction of 96 samples. The use of a disk as sorbent in the 96 well plate further improved the performance of SPE and allowed for small elution volumes, making it possible to 'dilute and shoot" after SPE elution. In this study, a 96 well plate (Empore) was developed, characterized and optimized for several pharmaceutical compounds. In addition, a robot (MultiProbe) was modified to automate the 96 well plate operation. Examples were given to illustrate the major differences of using 96 well disk plate SPE in the method development as compared to the traditional SPE. This technology has been successfully used to support many clinical studies. Typically, a batch of 96 samples were prepared in 1-1.5 hours unattended (except for the replacement of a collection plate). Considerable savings in disposable supplies were also noted.

Effects of levosimendan on left ventricular function: correlation with plasma concentrations in conscious dogs

OBJECTIVES

To test the hypothesis that the hemodynamic and left ventricular functional actions of levosimendan (Orion Pharmaceutica, Espoo, Finland), a new myofilament calcium sensitizer with phosphodiesterase-inhibiting properties, in conscious dogs are correlated with plasma concentrations of the drug measured with reverse-phase, high-performance liquid chromatography.

DESIGN

Prospective investigation.

SETTING

Research laboratory.

PARTICIPANTS

Fifteen chronically instrumented dogs.

INTERVENTIONS

On different experimental days, dogs were assigned to receive intravenous levosimendan (12 or 24 micrograms/kg loading dose and 0.2 or 0.4 microgram/kg/min infusion, respectively).

MEASUREMENTS AND MAIN RESULTS

Systemic and coronary hemodynamics, left ventricular function, and plasma concentrations were determined at scheduled intervals during and after levosimendan infusions. Levosimendan increased heart rate and cardiac output and decreased left ventricular end-diastolic pressure and systemic vascular resistance. Levosimendan caused dose-related enhancement of left ventricular systolic (increases in regional preload recruitable stroke work slope and +dP/dtmax) and diastolic functions (decreases in the time constant of isovolumic relaxation and regional chamber stiffness). The elimination half-life of levosimendan was 0.76 +/- 0.04 hours.

CONCLUSIONS

The hemodynamic actions and left ventricular functional effects of levosimendan correlated closely with plasma concentrations and returned to baseline values within 3 hours after discontinuation of the drug.

Automated analysis of levosimendan in human plasma by on-line dialysis and liquid chromatography

A fully automated method for quantitation of levosimendan, (R)-(-)-[[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl) phenyl]hydrazono]propanedinitrile, in human plasma is described. The method involves on-line dialysis of the samples, trace enrichment of the dialysates, and reversed-phase high-performance liquid chromatography with UV detection at 380 nm. An internal standard was used to compensate for variations in the dialysis rate caused by temperature fluctuations. The precision and accuracy of the method were good. The between-day variation (RSD) was 2.7% at a plasma concentration of 15 ng/mL and 1.7% at 450 ng/mL. The limit of quantitation was 5 ng/mL with an RSD of 4.0%. The completion time of the assay was 19 min.

Effects of MCI-154, a new cardiotonic Ca2+ sensitizer, on ventricular arrhythmias and membrane ionic currents

We examined whether a new positive inotropic agent with Ca(2+)-sensitizing activity, MCI-154, 6-[4-(4-pyridylamino)phenyl]-4, 5-dihydro-3-(2H)-pyridazinone hydrochloride trihydrate, had deleterious effects on ventricular arrhythmias, since several phosphodiesterase III inhibitors have been shown to aggravate arrhythmias in our earlier studies. Continuous infusion of MCI-154 (1 microgram/kg/min for 15 min) did not suppress or aggravate the arrhythmias generated in the two-stage coronary ligation-, digitalis- and adrenaline-induced canine arrhythmia models studied. Also in the case of a bolus injection of 30 micrograms/kg, MCI-154 did not aggravate the adrenaline-induced arrhythmias. To explain these results in vivo, a whole-cell voltage-clamp experiment on guinea-pig ventricular cells was performed. MCI-154 (10-100 microM) did not increase the inward Ca2+ current under the condition where these currents were increased by isoprenaline. These results indicate that MCI-154 does not aggravate ventricular arrhythmias and does not act on membrane currents associated with arrhythmogenesis. Thus, MCI-154 may become a useful positive inotropic agent with little arrhythmogenic effect.

Enantiomeric bioanalysis of simendan and levosimendan by chiral high-performance liquid chromatography

rac-Simendan, (+/-)-(R,S)-[[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)-phenyl ] hydrazono]propanedinitrile, and the levorotatory enantiomer levosimendan, are drug candidates intended for the treatment of congestive heart failure. An enantiospecific high-performance liquid chromatographic (HPLC) method suitable for determination of the ratio of the enantiomer concentrations in blood plasma samples was developed. Direct resolution of the enantiomers was achieved by using a chiral beta-cyclodextrin stationary phase in reversed phase mode. With an eluent containing 24-33% of methanol in a 0.5% (v/v) triethylammonium acetate buffer, pH 6.0, and a flow rate of 1 ml/min, a resolution (1.2-1.6) adequate for the determinations was achieved. By using UV detection, the relative concentration of the enantiomers in plasma was assessed down to 10 ng/ml. For the racemate, the results indicated a slightly enantioselective disposition and plasma protein binding in rat, dog, and man. The pure enantiomer, levosimendan, was found not to isomerize in vivo.

Pharmacokinetics and pharmacodynamics of simendan, a novel calcium sensitizer, in healthy volunteers

OBJECTIVE

To assess pharmacokinetics and correlation of pharmacokinetics and pharmacodynamics of simendan, a new calcium-sensitizing compound aimed at the treatment of congestive heart failure, in healthy volunteers.

METHODS

Simendan was administered to eight healthy subjects in seven different doses, and its concentrations in plasma and proportions of enantiomers (levosimendan and dextrosimendan) were determined. Hemodynamic effects were measured by M-mode echocardiography.

RESULTS

The area under the plasma concentration time-curve increased linearly and correlated with dose (p < 0.001). The volumes of distribution were small (mean VC, 8.5 to 14.1 L; VSS, 12.8 to 28.4 L) and elimination fairly fast (mean t1/2 beta, 0.83 to 1.77 hours). There were only minor differences between the pharmacokinetic profiles of the enantiomers of simendan. The increase in maximal ejection fraction (EF) correlated significantly with the plasma concentrations of simendan (p < 0.01; r2 = 0.33). However, the correlation coefficient was higher between estimated concentrations of simendan in peripheral compartment and ejection fraction; r2 was 0.79 (p < 0.01) and 0.94 (p < 0.001) after 2 and 5 mg doses, respectively. One subject after 5 mg simendan and one subject after 10 mg simendan had transient vasovagal reactions consisting of decreases in heart rate and blood pressure.

CONCLUSIONS

Simendan has favorable and predictable hemodynamic actions. The pharmacokinetic profile facilitates rapid dose adjustments during intravenous administration.

Pharmacokinetics and bioavailability of bemoradan, a long-acting inodilator in healthy males

Bemoradan is a potent, long-acting orally active inodilator. The pharmacokinetics and bioavailability of bemoradan were studied in twelve normal males following oral administration of single, ascending doses of the bemoradan HCL salt in capsules. Plasma and urine levels of bemoradan were determined by HPLC (detection limits: approximately 0.5 ng/ml for plasma and 5 ng/ml for urine). Bemoradan was rapidly absorbed from the capsule formulation at all doses (Cmax occurred at 2.1-2.4 hours). Bemoradan was slowly eliminated from the body (harmonic mean t1/2 16-23 hours). There was a dose-proportional increase in the AUC (0-48) values of bemoradan in humans following the administration of 0.5, 1, 1.5 and 2 mg of bemoradan. The AUC (0-48) values increased to 2.3, 3.4 and 4.0 times when the dose was increased to 2, 3 and 4 times. Urinary excretion of unchanged bemoradan accounted for approximately 5-12% of the dose. Results from this study and previous studies in rats and dogs indicate that bemoradan is well and rapidly absorbed after oral dosing, has linear pharmacokinetics and long elimination half-lives across species.

Preclinical pharmacology of 1069C85, a novel tubulin binder

The compound 1069C85, methyl N-[6-(3,4,5-trimethoxybenzyloxy)imidazo(1,2b)-pyridazin-2-yl ] carbamate, is a novel synthetic tubulin binder currently undergoing phase I clinical trial. It was developed with a view to overcoming multidrug resistance and is given orally. Cytotoxicity studies in vitro against human ovarian carcinoma cell lines showed a lack of cross-resistance with cisplatin and no cross-resistance in two doxorubicin-resistant cell lines that exhibit high levels of resistance to both paclitaxel and vinblastine. Pharmacokinetic studies in BALB/c mice showed the oral bioavailability to be 20%, with 35% of the drug being excreted unchanged in the faeces over the first 24 h. Maximal plasma concentrations (Cmax) were achieved within 2 h of oral administration as compared with 7.5 min following i.v. injection. At a dose of 20 mg/kg, the tumour drug concentration exceeded the plasma Cmax by a factor of 1.5 and was within the in vitro cytotoxic concentration range. The drug showed a linear relationship between the dose and the area under the plasma concentration versus time curve (AUC) for doses of up to 20 mg/kg, above which no further increase in AUC was observed, possibly due to saturable absorption. 1069C85 is highly protein-bound (85%-99%) and appears to be subject to metabolism. The demonstration of cytotoxic activity against multidrug-resistant human tumour cell lines and the detection of potentially cytotoxic levels in an experimental tumour following oral administration support the choice of 1069C85 for clinical development.

Simultaneous determination of the enantiomers of pimobendan and its main metabolite in rat plasma by high-performance liquid chromatography

A high-performance liquid chromatographic method for the simultaneous analysis of the enantiomers of pimobendan and its main metabolite, with an n-hexane-ethanol-acetic acid solvent system, has been developed. After solid-phase extraction from plasma, the enantiomers were separated from each other using a Sumichiral OA-4400 column, which is commercially available and contains a chiral stationary phase composed of (S)-proline and (S)-1-(alpha-naphthyl)ethylamine coated on silica. The enantiomers were detected with a fluorescence detector (excitation at 330 nm, emission at 415 nm). The intra- and inter-day precision studies showed good reproducibilities: the coefficients of variation were less than 10.3% for pimobendan enantiomers and 13.0% for metabolite enantiomers. The calibration curves were linear (r2 > 0.996) in the concentration range 1.25-200 ng/ml. The minimum measurable level was 125 pg per 100 microliters of plasma. The method was used in a preliminary pharmacokinetic study in three male rats after intravenous administration of racemic pimobendan (2 mg/kg).

Simultaneous monitoring of bemoradan pharmacokinetics and hemodynamics in mongrel dogs

This study was designed to determine the relationship between the hemodynamic responses to bemoradan, a novel cardiotonic agent, and its plasma levels after single administration of an oral dose or a 15 minute i.v. infusion to mongrel dogs, and to demonstrate that the clinical capsule formulation of bemoradan elicits a pharmacological response in the dog. Four conscious, instrumented mongrel dogs received each of four bemoradan treatments (30 micrograms kg-1 i.v., 100 micrograms kg-1 i.v., 100 micrograms kg-1 suspension p.o., or 1 mg capsule p.o.) in a Latin square cross-over design. Plasma levels of bemoradan up to 24 h post-dosing were determined by HPLC. Cardiac contractility (dP/dt), heart rate, and arterial blood pressure were continuously monitored for 8 h and again at 24 h. Results of the study indicate that there was a significant correlation between bemoradan plasma levels and dP/dt. The 1 mg clinical capsule formulation was well absorbed when compared to an oral suspension and an i.v. dose. Peak increases in dP/dt of 64 per cent at 15 min for the suspension and 53 per cent at 1 h for the capsule were observed.

Sensitive determination of the phosphodiesterase III/IV inhibitor zardaverine in human serum by direct sample injection, automated precolumn clean-up and high-performance liquid chromatography

A high-performance liquid chromatographic method is described for the determination of the phosphodiesterase III/IV inhibitor zardaverine in serum by using fully automated clean-up of large-volume serum samples on a semi-preparative-scale precolumn followed by chromatography on two analytical columns operated with two different solvent systems. The switching of the analytical columns provides the necessary specificity and sufficient sensitivity for UV detection is obtained by the sample volume. The method was shown to give nearly quantitative recovery, allowing the use of external standard quantification. Good precision and linearity within the concentration range 1-50 ng/ml could be demonstrated. The method is suitable for routine measurements in support of kinetic studies of zardaverine in man.

Pharmacokinetics of cadralazine in a large group of hypertensive patients chronically treated with cadralazine: advantage over a conventional study in a small group of patients

The concentrations of cadralazine in plasma were studied in 101 hypertensive patients treated with oral doses of 10, 15, or 20 mg of cadralazine once daily. Most of the patients received additionally a beta-blocking drug (n = 87) and a diuretic (n = 52). Few blood samples were collected in each patient on several occasions during the treatment, which usually lasted for more than 6 months. No accumulation of cadralazine in plasma occurred in any of the patients and the maximum concentrations were similar to those recorded in a small sample of healthy volunteers. The terminal half-life of elimination (3.6 h) was longer than that observed in healthy subjects (approximately 2.5 h). Conversely, the total clearance (197 ml/min) was lower (285 ml/min in healthy). The half-life and the total clearance in plasma were not dose dependent. In the patients treated for more than 6 months, no change in the pharmacokinetics of cadralazine was detected. The description of the distribution of concentrations showed that one-half of the patients behaved similarly to healthy subjects concerning half-life and total clearance. The other half presented a slower elimination of the drug (t 1/2 = 4.4 h and ClT = 130 ml/min) and these patients were significantly older (p = 0.01) than the former. This suggests that special attention should be paid to old hypertensive patients when a dose higher than 15 mg once daily is prescribed. Though concentrations were proportional to the dose, the body weight was not found to be a determining factor for dose adjustment.(ABSTRACT TRUNCATED AT 250 WORDS)

A sensitive high performance liquid chromatography microassay for bemoradan, a novel cardiotonic agent, in plasma/serum using a semi-automatic liquid/solid extraction sample preparation system--AASP

A high performance liquid chromatographic method for the measurement of bemoradan levels in plasma/serum is described. This method uses Varian's AASP (Varian Associates, Sunnyvale, CA, USA), a semi-automatic liquid/solid extraction sample preparation system. It requires only small volumes of plasma/serum samples (0.2-1 mL) and needs no organic solvent for sample preparation. The mean recovery of bemoradan at plasma or serum concentrations of 0.5-100 ng/mL is 82%. The assay has a detection limit of 0.5 ng/mL (when 1 mL of plasma/serum is used) and is linear in the concentration range 0.5-500 ng/mL.

Pharmacokinetics of cilazapril during repeated oral dosing in healthy young volunteers

The pharmacokinetics of cilazapril and its active metabolite cilazaprilat in plasma were investigated in an open study of 13 healthy male volunteers, aged 18 to 43 years. One capsule containing 2.5 mg cilazapril was administered to each volunteer daily for 8 days. Plasma samples were obtained after the first and eighth doses. Concentrations of cilazapril, cilazaprilat and activities of angiotensin converting enzyme (ACE) were measured by radioenzymatic methods. For cilazapril, the values of apparent plasma clearance (about 15 l/h) and volume of distribution (around 28 l) were sufficiently high to suggest that significant pre-systemic hydrolysis to cilazaprilat occurred. There were no significant changes in these values after repeated dosing. There were small, but statistically significant, increases in mean peak concentrations, mean areas under concentration-time curves and mean trough concentrations from the first to the eighth dose. A steady state was achieved after eight doses with an accumulation of 20-30%. The mean effective half-life was approximately 9 h. Despite the accumulation of cilazaprilat in plasma, there were no significant differences in plasma ACE inhibition from the first to the eighth dose.

Cardiovascular effects and plasma level profile of pimobendan (UD-CG 115 BS) and its metabolite UD-CG 212 in patients with congestive heart failure after single and repeated oral dosing

Pimobendan (10 mg on day 1, then 5 mg twice daily for 28 days) was administered orally to nine patients in class III-IV stable congestive heart failure. On day 1, pimobendan appeared in plasma within 30 min, its plasma concentration peaked at 39 +/- 23 ng/ml after 1.5 h, and then decreased with a half-life of 1.44 +/- 0.94 h. Concentrations of its major metabolite UD-CG 212 peaked 3 h after drug intake, at 24 +/- 7 ng/ml. The time course of plasma concentrations was similar on days 1, 2, and 28. Cardiac index increased from 2.2 +/- 0.5 to 2.8 +/- 0.4 L.min-1.m-2 (p = 0.0001) on day 1, from 2.8 +/- 0.5 to 3.4 +/- 0.4 L.min-1.m-2 (p = 0.0032) on day 2, and stayed at 2.7 +/- 0.6 and 2.7 +/- 0.9 L.min-1.m-2 (p = 0.7895) on day 28. On day 1, pulmonary capillary wedge pressure decreased from 16 +/- 7 to 6 +/- 5 mm Hg (p = 0.0001), from 10 +/- 7 to 7 +/- 8 mm Hg (p = 0.0001) on day 2, and from 9 +/- 7 to 5 +/- 3 mm Hg (p = 0.0275) on day 28. Cardiovascular effects of pimobendan were independent of plasma concentrations. All patients improved by at least one NYHA functional class; exercise tolerance increased. No side effect was observed, but two patients died suddenly: Arrhythmogenicity should be ruled out before pimobendan is recommended for treatment of heart failure.

Determination of cadralazine in human whole blood using reversed-phase high-performance liquid chromatography: utilizing a salting-out extraction procedure

A rapid, selective, and sensitive ion-paired reversed-phase high-performance liquid chromatographic method for determination of the new carbazate type of antihypertensive vasodilator agent cadralazine in human whole blood has been developed. Cadralazine was extracted from whole blood by adding 0.5 ml of acetonitrile to 1.0 ml of whole blood followed by salting-out of acetonitrile by the addition of potassium carbonate in excess. An aliquot of the salted-out acetonitrile was injected into the chromatographic system. A column packed with 3-microns octyl (C8) particles was used with an isocratic elution of 1% acetic acid and 5 mM hexanesulfonic acid-acetonitrile (70:30, v/v). The cadralazine was measured using ultraviolet detection at 250 nm and the assay was completed in less than 20 min and had a limit of quantitation of 10 ng/ml for a 100-microliters injection volume.

Protein binding of quinolonecarboxylic acids. I. Cinoxacin, nalidixic acid and pipemidic acid

Binding of cinoxain (CINX), nalidixic acid (NA) and pipemidic acid (PPA) to serum proteins was investigated by equilibrium dialysis, ultrafiltration and circular dichroism (CD) spectroscopy. CINX and NA were found to bind mainly to albumin in human serum, the latter interacting with the protein about ten times as strongly as CINX at pH 7.4 and 37 degrees C. PPA showed little or no significant binding to human serum albumin (HSA), alpha 1-acid glycoprotein, and globulins, but showed 20-30% binding to protein in human serum. The CD results were suggestive of some weak interaction of PPA with human apotransferrin. Binding of the three drugs to HSA was found to depend on the lipophilicity of their substituents at the 7-position. The degree of protein binding for human, dog and rat sera at 37 degrees C was in the order of NA (92-97%) greater than CINX (68-90%) greater than PPA (20-30%) at drug concentrations of 10-30 micrograms/ml. CINX showed relatively large species dependence in serum protein binding, which seemed to be due to different affinities of this drug to the respective albumins. CINX was found to bind to rat serum albumin as strongly as NA.

Protein binding of quinolonecarboxylic acids. II. Spectral changes on the interaction of cinoxacin, nalidixic acid and pipemidic acid with human and rat albumins

The interaction of cinoxacin (CINX), nalidixic acid (NA), and pipemidic acid (PPA) with human and rat serum albumins (HSA and RSA) was studied by UV difference absorption and circular dichroism (CD) spectroscopy. CINX and NA bound to the albumins and generated difference absorption and induced CD (ICD) spectra. The difference absorption spectral data explained reasonably our previous observations that CINX bound to HSA more weakly than NA, but to RSA as strongly as NA. We used a quantity delta epsilon/epsilon, designated as relative molar difference absorbance, at positions corresponding to the longest wavelength peaks in the difference spectra. The quantity was found to correlate linearly with percent bound to both HSA and RSA, but with different slopes, from which the binding site for CINX and NA in RSA was supposed to provide a much more nonpolar environment than that in HSA. The magnitude of ICD bands observed at 371 nm for CINX and at 342-348 nm for NA corresponded to the binding degrees of these drugs to both albumins. Anisotropy factors for the ICD bands at 350-271 nm for CINX and 320-348 nm for NA were approximately similar between HSA and RSA, suggesting a similar ability to generate the ICD spectra in these wavelength regions upon binding to the albumins. Spectral results for PPA in albumin solutions showed little or no binding of this drug to HSA and RSA. PPA existed as a betaine form in neutral solution and its positively charged group acted as an unfavorable factor for binding to both albumins.

The pharmacokinetics and dose proportionality of cilazapril

1. The pharmacokinetics and dose proportionality of cilazapril, an orally active angiotensin-converting enzyme (ACE) inhibitor, were investigated in a four-way randomized crossover study in 24 volunteers, over the 0.5 to 5 mg dose range intended for therapeutic use. 2. Plasma concentrations of cilazapril and of the active metabolite cilazaprilat together with plasma ACE activity were determined by radio-enzymatic assay. 3. Plasma concentrations of both cilazapril and cilazaprilat increased in proportion to dose over the range studied. All doses produced substantial inhibition of ACE. Higher doses were associated with earlier onset and longer duration of maximal effect.

A pharmacokinetic study of cilazapril in elderly and young volunteers

1. Cilazaprilat is an inhibitor of angiotensin converting enzyme (ACE) and is the active metabolite of cilazapril. The pharmacokinetics of cilazaprilat, and the inhibition of plasma ACE were investigated in 12 elderly and 12 young healthy volunteers. 2. Single oral 1 mg doses of cilazapril were given to the elderly (age range 65-83 years) and the young (age range 18-31 years) in an open study. Plasma and urinary cilazaprilat concentrations, and plasma ACE activities were measured up to 72 h after dosing by radioenzymatic methods. 3. Cilazapril was well tolerated in both young and elderly subjects. Small falls in blood pressure were observed up to 8-24 h after dosing. 4. The mean peak plasma cilazaprilat concentration in the elderly (11.5 ng ml-1) was significantly greater (P less than 0.02) than the corresponding value in the young (8.3 ng ml-1). Total and renal clearances were significantly lower (both P less than 0.05) in the elderly (12.8 and 5.11 h-1) than in the young (16.0 and 7.21 h-1). Total urinary recovery of cilazaprilat was similar for the two groups at about 43% of dose. 5. Plasma ACE inhibition was slightly greater in the elderly but the mean inhibition in the two groups did not differ by more than 10% at any time-point from 1-72 h. 6. The plasma concentrations of cilazaprilat required for 90% ACE inhibition were similar at 4.7 and 4.8 ng ml-1 in the elderly and young respectively. 7. It is concluded that the age-related changes in cilazaprilat kinetics and in the degree of ACE inhibition are small.(ABSTRACT TRUNCATED AT 250 WORDS)