Discovery of novel brain permeable and G protein-biased beta-1 adrenergic receptor partial agonists for the treatment of neurocognitive disorders

The beta-1 adrenergic receptor (ADRB1) is a promising therapeutic target intrinsically involved in the cognitive deficits and pathological features associated with Alzheimer's disease (AD). Evidence indicates that ADRB1 plays an important role in regulating neuroinflammatory processes, and activation of ADRB1 may produce neuroprotective effects in neuroinflammatory diseases. Novel small molecule modulators of ADRB1, engineered to be highly brain permeable and functionally selective for the G protein with partial agonistic activity, could have tremendous value both as pharmacological tools and potential lead molecules for further preclinical development. The present study describes our ongoing efforts toward the discovery of functionally selective partial agonists of ADRB1 that have potential therapeutic value for AD and neuroinflammatory disorders, which has led to the identification of the molecule STD-101-D1. As a functionally selective agonist of ADRB1, STD-101-D1 produces partial agonistic activity on G protein signaling with an EC50 value in the low nanomolar range, but engages very little beta-arrestin recruitment compared to the unbiased agonist isoproterenol. STD-101-D1 also inhibits the tumor necrosis factor α (TNFα) response induced by lipopolysaccharide (LPS) both in vitro and in vivo, and shows high brain penetration. Other than the therapeutic role, this newly identified, functionally selective, partial agonist of ADRB1 is an invaluable research tool to study mechanisms of G protein-coupled receptor signal transduction.

In silico-in vitro-in vivo studies of experimentally designed carvedilol loaded silk fibroin-casein nanoparticles using physiological based pharmacokinetic model

The study aimed to design and develop carvedilol loaded silk fibroin-casein nanoparticles using 3² full factorial design. Silk fibroin and casein concentration were selected as the independent variables and their effect were observed on dependent variables: particle size, polydispersity index, encapsulation efficiency, drug release, and dissolution efficiency. The developed optimized formulation was characterized using fourier transform infrared spectroscopy, differential scanning calorimetry, and Powder X-ray diffraction. Surface morphology of optimized formulation using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy revealed spherical nature of particles without any evidence of aggregation. The optimized formulation showed a 2.04-fold increase in C_max, and 6.87-fold increase in bioavailability as compared to aqueous suspension. The formulation showed sustained release as confirmed by increases in mean residence time. The in vivo in silico simulation using physiologically based pharmacokinetics (PBPK) model and population simulation (100 subjects) revealed a reasonable degree of superimposition of simulated and observed pharmacokinetic parameters based on overall fold error (≤2.0). The enhanced bioavailability with sustained effect demonstrates potential of silk fibroin as an alternative carrier for drug delivery and presents Gastoplus™ as efficient tool for in vivo in silico simulations.

Low heritability in pharmacokinetics of talinolol: a pharmacogenetic twin study on the heritability of the pharmacokinetics of talinolol, a putative probe drug of MDR1 and other membrane transporters

BACKGROUND

Efflux transporters like MDR1 and MRP2 may modulate the pharmacokinetics of about 50 % of all drugs. It is currently unknown how much of the variation in the activities of important drug membrane transporters like MDR1 or MRP2 is determined by genetic or by environmental factors. In this study we assessed the heritability of the pharmacokinetics of talinolol as a putative probe drug for MDR1 and possibly other membrane transporters.

METHODS

Talinolol pharmacokinetics were investigated in a repeated dose study in 42 monozygotic and 13 same-sex dizygotic twin pairs. The oral clearance of talinolol was predefined as the primary parameter. Heritability was analyzed by structural equation modeling and by within- and between-subject variance and talinolol clearance was correlated with polymorphisms in MDR1, MRP2, BCRP, MDR5, OATP1B1, and OCT1.

RESULTS

Talinolol clearance varied approximately ninefold in the studied sample of healthy volunteers. The correlation of clearances between siblings was not significantly different for the monozygotic and dizygotic pairs. All data analyses consistently showed that variation of talinolol pharmacokinetics was mainly determined by environmental effects. Structural equation modeling attributed 53.5 % of the variation of oral clearance to common environmental effects influencing both siblings to the same extent and 46.5 % to unique environmental effects randomly affecting individual subjects. Talinolol pharmacokinetics were significantly dependent on sex, body mass index, total protein consumption, and vegetable consumption.

CONCLUSIONS

The twin study revealed that environmental factors explained much more of the variation in pharmacokinetics of talinolol than genetic factors.

TRIAL REGISTRATION

European clinical trials database number: EUDRA-CT 2008-006223-31. Registered 26 September 2008. ClinicalTrials.gov number: NCT01845194 .

Pharmacodynamics ofβ-Blockers in Heart Failure: Lessons from the Carvedilol Or Metoprolol European Trial

Heart failure is a growing public health problem in the United States, and the approach to the treatment of heart failure has undergone a radical transformation in the past decade. The use of β-blocker therapy in heart failure patients is now widely recommended, based on evidence from large-scale clinical trials demonstrating that bisoprolol, carvedilol, and extended-release metoprolol succinate significantly reduce morbidity and mortality in patients with heart failure. Although these agents appear to provide similar benefits, the question remains whether pharmacologic differences among them could translate to differences in clinical outcomes. The Carvedilol Or Metoprolol European Trial (COMET) compared nonselective blockade of the β1-/β2-/α1-adrenergic receptors with carvedilol versus selective β1-blockade with immediate-release metoprolol tartrate in patients with chronic heart failure. The trial found that carvedilol significantly reduced all-cause mortality compared with immediate-release metoprolol tartrate, although there were no differences in hospitalizations. Herein we review the pharmacokinetics and pharmacodynamics of metoprolol and carvedilol. In doing so, several issues regarding the design of COMET are identified that could alter the interpretation of the results of this trial. These include the choice of dose and dosage regimen of immediate-release metoprolol tartrate, a dosage form that has never been shown to reduce mortality in patients with heart failure. Additional studies are needed to fully understand whether there are any advantages of selective versus nonselective adrenergic blockade and whether there are any clinically meaningful differences in effectiveness between β-blockers with proven benefit in the management of chronic heart failure. The results of COMET demonstrate that all β-blockers and dosage forms are not interchangeable when prescribed for heart failure. Clinicians should choose only those agents (and dosage forms) that have been proven to reduce mortality in this patient population.

Effects of cilostazol on the pharmacokinetics of carvedilol after oral and intravenous administration in rats

This study was designed to investigate the effects of cilostazol on the pharmacokinetics of carvedilol following oral or intravenous administration of carvedilol in rats. Clinically carvedilol and cilostazol can be prescribed for treatment of cardiovascular diseases. Carvedilol and cilostazol are all substrates of CYP2C9 enzymes. Carvedilol was administered orally or intravenously without or with oral administration of cilostazol to rats. The effects of cilostazol on cytochrome P450 (CYP) 2C9 activity and P-gp activity were also evaluated. Cilostazol inhibited CYP2C9 activity in a concentration-dependent manner with 50% inhibitory concentration (IC(50)) of 8.7 μM. Compared with the control group, the area under the plasma concentration-time curve (AUC) of carvedilol was significantly (P < 0.05) increased by 38.0%. The peak concentration (C(max)) was significantly (P < 0.05) increased by 49.2% in the presence of cilostazol after oral administration of carvedilol. Consequently, the relative bioavailability (R.B.) of carvedilol was increased by 1.15 - 1.38-fold, and the absolute bioavailability (A.B.) of carvedilol in the presence of cilostazol was significantly (P < 0.05) higher than that of the control. After intravenous administration, the AUC of carvedilol was significantly (P < 0.05) increased by 19.2% compared to that in the control by cilostazol. These results suggest that cilostazol effectively inhibited the metabolism of carvedilol. The increased oral bioavailability of carvedilol might be due to the inhibition of CYP2C9-mediated metabolism of carvedilol in the liver by cilostazol.

Development and optimization of carvedilol orodispersible tablets: enhancement of pharmacokinetic parameters in rabbits

BACKGROUND

Carvedilol (CVD) is used for the treatment of essential hypertension, heart failure, and systolic dysfunction after myocardial infarction. Due to its lower aqueous solubility and extensive first-pass metabolism, the absolute bioavailability of CVD does not exceed 30%. To overcome these drawbacks, the objective of this work was to improve the solubility and onset of action of CVD through complexation with hydroxypropyl-β-cyclodextrin and formulation of the prepared complex as orodispersible tablets (ODTs).

METHODS

Compatibility among CVD and all tablet excipients using differential scanning calorimetry and Fourier transform infrared spectroscopy, complexation of CVD with different polymers, and determination of the solubility of CVD in the prepared complexes were first determined. A Box-Behnken design (BBD) was used to study the effect of tablet formulation variables on the characteristics of the prepared tablets and to optimize preparation conditions. According to BBD design, 15 formulations of CVD-ODTs were prepared by direct compression and then evaluated for their quality attributes. The relative pharmacokinetic parameters of the optimized CVD-ODTs were compared with those of the marketed CVD tablet. A single dose, equivalent to 2.5 mg/kg CVD, was administered orally to New Zealand white rabbits using a double-blind, randomized, crossover design.

RESULTS

The solubility of CVD was improved from 7.32 to 22.92 mg/mL after complexation with hydroxypropyl-β-cyclodextrin at a molar ratio of 1:2 (CVD to cyclodextrin). The formulated CVD-ODTs showed satisfactory results concerning tablet hardness (5.35 kg/cm(2)), disintegration time (18 seconds), and maximum amount of CVD released (99.72%). The pharmacokinetic data for the optimized CVD-ODT showed a significant (P<0.05) increase in maximum plasma concentration from 363.667 to 496.4 ng/mL, and a shortening of the time taken to reach maximum plasma concentration to 2 hours in comparison with the marketed tablet.

CONCLUSION

The optimized CVD-ODTs showed improved oral absorption of CVD and a subsequent acceleration of clinical effect, which is favored for hypertensive and cardiac patients.

Assessment of sex differences in Pharmacokinetics of carvedilol in human

Carvedilol is an anti-hypertensive agent capable of blocking both alph (α) and beta (β) receptors used to preclude cardiac arrhythmias and angina. The study was designed to evaluate the Pharmacokinetics of carvedilol in human male and female volunteers. Healthy male and female (twenty each) volunteers were finalized for the study after preliminarily clinical examination. Blood samples were collected at specific time intervals after giving an oral dose of 12.5mg carvedilol, separated the plasma and placed at -80°C until analysis. Estimation of carvedilol in human plasma was accomplished by High performance liquid chromatographic (HPLC) method using fluorescent detector. Plasma concentration-time curve was used for calculation of pharmacokinetic parameters using two-compartment open model. Mean (SD) values of AUC and Cmax 0.076±0.021βg.h/ml and 0.024±0.005βg/mL, respectively) in male differ significantly (P<0.05) from the female 0.197±0.042βg.h/ml and 0.048±0.02βg/mL, respectively). Overall, bioavailability of carvedilol was somewhat higher in females than in males, but these differences could be expounded by the lower body weight of female. Conversely, no significant differences were found for tmax, clearance and half-life in male and female. Moreover the ethnicity had significant impact on the Pharmacokinetics of carvedilol in human.

Carvedilol: use in chronic heart failure

Carvedilol is a beta-adrenergic antagonist with vasodilatory properties (alpha1-antagonism), which has been extensively evaluated in the treatment of patients with heart failure. In patients with chronic heart failure carvedilol improves left-ventricular (LV) ejection fraction over 6 to 12 months of treatment, and attenuates LV remodelling. Large-scale randomised, placebo controlled trials involving more than 4000 patients with chronic heart failure have demonstrated that carvedilol improves survival and reduces hospitalizations. Comparative studies with metoprolol in patients with heart failure have suggested that carvedilol may be associated with greater survival benefit although differences in the preparation of metoprolol have left uncertainty in this area. Carvedilol has a high safety profile and the clinical benefits appear maintained across a wide range of patients with comorbidities such as diabetes and renal failure. Carvedilol has also been shown to attenuate LV remodeling and improve clinical outcomes in patients with LV dysfunction and/or heart failure following acute myocardial infarction. As a result of these data, carvedilol is recommended for treatment of patients with heart failure in heart-failure guidelines. This evidence-based treatment should be widely implemented to ensure that patients with heart failure receive appropriate medical therapy.

Physicochemical profiling of new aminopropan-2-ol derivatives with beta-adrenolytic activity: the importance for pharmacokinetic properties

A convenient procedure has been developed for the determination of dissociation constants (pKa) and partition (log P) and distribution (log D) coefficients of three new aminopropan-2-ol derivatives with beta-adrenolytic activity briefly called 2F109, ANBL and TWo8. The apparent acid dissociation constant (psKa) in these water-insoluble compounds was determined potentiometrically in dimethylformamide-water, dimethyl sulfoxide-water and methanol-water mixtures at a temperature of 25 degrees C. The aqueous pKa values assessed by Yasuda-Shedlovsky extrapolation were 8.64 +/- 0.06, 8.85 +/- 0.51 and 8.26 +/- 0.45 for 2F109, ANBL and TWo8, respectively. Lipophilicity expressed by chromatographic retention factor was determined by reversed phase liquid chromatography at pH 10.5 using a Zorbax Extend C18 column (log k10.5), and at pH 7.4 using an immobilized artificial membrane IAM.PC.DD2 column (log k7.4), respectively. The log k of each compound extrapolated to 100% aqueous phase (log kw10.5 and and log kw7.4) were corrected with log P and log D of acebutolol, atenolol, metoprolol,pindolol, propranolol and sotalol used as the model drugs.

Nanosuspension based in situ gelling nasal spray of carvedilol: development, in vitro and in vivo characterization

The objective of the present investigation was to develop in situ gelling nasal spray formulation of carvedilol (CRV) nanosuspension to improve the bioavailability and therapeutic efficiency. Solvent precipitation-ultrasonication method was opted for the preparation of CRV nanosuspension which further incorporated into the in situ gelling polymer phase. Optimized formulation was extensively characterized for various physical parameters like in situ gelation, rheological properties and in vitro drug release. Formation of in situ gel upon contact with nasal fluid was conferred via the use of ion-activated gellan gum as carrier. In vivo studies in rabbits were performed comparing the nasal bioavailability of CRV after oral, nasal, and intravenous administration. Optimized CRV nanosuspension prepared by combination of poloxamer 407 and oleic acid showed good particle size [d (0.9); 0.19 μm], zeta potential (+10.2 mV) and polydispersity (span; 0.63). The formulation containing 0.5% w/v gellan gum demonstrated good gelation ability and desired sustained drug release over period of 12 h. In vivo pharmacokinetic study revealed that the absolute bioavailability of in situ nasal spray formulation (69.38%) was significantly increased as compared to orally administered CRV (25.96%) with mean residence time 8.65 h. Hence, such in situ gel system containing drug nanosuspension is a promising approach for the intranasal delivery in order to increase nasal mucosal permeability and in vivo residence time which altogether improves drug bioavailability.

Novel chitosan-functionalized spherical nanosilica matrix as an oral sustained drug delivery system for poorly water-soluble drug carvedilol

A novel spherical nanosilica matrix (SNM) together with chitosan (CTS) encapsulated SNM (CTS-SNM) was developed in order to investigate the feasibility of using chitosan to regulate drug release rate from porous silica and obtain an oral sustained drug delivery system. To achieve this goal, we synthesized a spherical nanosilica matrix (SNM) and incorporated chitosan chains on the SNM surface. Solvent evaporation method was adopted to load the model drug carvedilol into SNM and CTS-SNM. The physicochemical properties of the drug carriers and drug-loaded composites were systematically studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption, X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The structural changes in CTS-SNM in simulated gastrointestinal fluid as well as the relationships between swelling effect of chitosan and in vitro drug release behaviors were investigated. Pharmacokinetic and bioavailability aspects were also discussed. The results showed that the powerful dispersing effect of SNM and the blocking action due to the swelling of chitosan were the two main factors contributing to the sustained drug release behavior. The swelling effect of chitosan in an acidic environment together with the shrinking effect in a relatively alkaline environment allowed regulation of drug release behavior in simulated gastrointestinal fluid. An in vivo study showed that the bioavailability of CAR was improved 182% compared with that of the commercial capsule when SNM was used as the drug carrier. As for CAR-CTS-SNM, the T(max) of CAR was delayed by about 3.4 h and the bioavailability was slightly increased in comparison with the commercial capsule. We believe that SNM and CTS-SNM developed in this study will help increase the use of polymers and inorganic materials in pharmaceutical applications and stimulate the design of oral drug delivery systems for immediate or sustained release of poorly water-soluble drugs.

A simplified protocol employing elacridar in rodents: a screening model in drug discovery to assess P-gp mediated efflux at the blood brain barrier

In the present study we have developed a simple, time, and cost effective in vivo rodent protocol to screen the susceptibility of a test compound for P-glycoprotein (P-gp) mediated efflux at the blood brain barrier (BBB) during early drug discovery. We used known P-gp substrates as test compounds (quinidine, digoxin, and talinolol) and elacridar (GF120918) as a chemical inhibitor to establish the model. The studies were carried out in both mice and rats. Elacridar was dosed intravenously at 5 mg/kg, 0.5 h prior to probe substrate administration. Plasma and brain samples were collected and analyzed using UPLC-MS/MS. In the presence of elacridar, the ratio of brain to plasma area under the curve (B/P) in mouse increased 2, 4, and 38-fold, respectively, for talinolol, digoxin, and quinidine; whereas in rat, a 70-fold increase was observed for quinidine. Atenolol, a non P-gp substrate, exhibited poor brain penetration in the presence or absence of elacridar in both species (B/P ratio ~ 0.1). Elacridar had no significant effect on the systemic clearance of digoxin or quinidine; however, a trend towards increasing volume of distribution and half life was observed. Our results support the utility of elacridar in evaluation of the influence of P-gp mediated efflux on drug distribution to the brain. Our protocol employing a single intravenous dose of elacridar and test compound provides a cost effective alternative to expensive P-gp knockout mice models during early drug discovery.

Effects of myricetin on the bioavailability of carvedilol in rats

CONTEXT

As an inhibitor of CYP2C9, CYP2D6 and P-gp, myricetin might affect the bioavailability of carvedilol when myricetin and carvedilol are used concomitantly for the prevention or therapy of cardiovascular diseases as a combination therapy. However, the effect of myricetin on the pharmacokinetics of carvedilol has not been reported in vivo.

OBJECTIVE

This study investigated the effects of myricetin on the pharmacokinetics of carvedilol after oral or intravenous administration of carvedilol in rats.

MATERIALS AND METHODS

Carvedilol was administered orally or intravenously with or without oral administration of myricetin to rats.

RESULTS

The effects of myricetin on P-gp, CYP2C9 and 2D6 activity were evaluated. Myricetin inhibited CYP2C9 and CYP2D6 enzyme activity with IC50 of 13 and 57 μM, respectively. In addition, myricetin significantly enhanced the cellular accumulation of rhodamine-123 in MCF-7/ADR cells overexpressing P-gp. Compared with the control group, the AUC was significantly increased by 52.0-85.1%, and the C(max) was significantly increased by 93.1-133.4% in the presence of myricetin after oral administration of carvedilol. Consequently, the relative bioavailability of carvedilol was increased by 1.17- to 1.85-fold and the absolute bioavailability of carvedilol in the presence of myricetin was increased by 18.1-86.4%. T(max) was significantly decreased.

DISCUSSION AND CONCLUSION

The enhanced oral bioavailability of carvedilol may result from both inhibition of CYP2C9 or CYP2D6-mediated metabolism and P-gp-mediated efflux of carvedilol in small intestine and/or in liver by myricetin rather than reducing renal elimination. Concomitant use of myricetin or myricetin-containing dietary supplements with carvedilol will require close monitoring for potential drug interactions.

In vivo probes of drug transport: commonly used probe drugs to assess function of intestinal P-glycoprotein (ABCB1) in humans

Intestinal P-glycoprotein (P-gp, ABCB1) may significantly influence drug absorption and elimination. Its expression and function is highly variable, regio-selective and influenced by genetic polymorphisms, drug interactions and intestinal diseases. An in vivo probe drug for intestinal P-gp should a registered, safe and well tolerated nonmetabolized selective substrate with low protein binding for which P-gp is rate-limiting during absorption. Other P-gp dependent processes should be of minor influence. The mechanism(s) and kinetics of intestinal uptake must be identified and quantified. Moreover, the release properties of the dosage form should be known. So far, the cardiac glycoside digoxin and the ß₁-selective blocker talinolol have been used in mechanistic clinical studies, because they meet most of these criteria. Digoxin and talinolol are suitable in vivo probe drugs for intestinal P-gp under the precondition, that they are used as tools in carefully designed pharmacokinetic studies with adequate biometrically planning of the sample size and that several limitations are considered in interpreting and discussion of the study results.

In vitro and in vivo evaluation of the effects of duloxetine on P-gp function

OBJECTIVE

To evaluate the effect of duloxetine (DLX) on the P-glycoprotein (P-gp) function in vitro and in vivo.

METHOD

In vitro experiment was conducted using the Caco-2 cell, a human colon cancer cell line that naturally expresses the P-gp and P-gp function was evaluated by monitoring whether DLX affect the accumulation of Rhd123. In vivo study was conducted by quantitating the effect of orally administered DLX on the bioavailability of talinolol.

RESULTS

In the in vitro study, incubation of Caco-2 cell with DLX caused a concentration-dependent increase in the accumulation of Rhd123. In the in vivo study, co-administration of DLX increased the bioavailability of talinolol. The ratio (90% confidence intervals) of AUC(0-60), AUC(0-∞), and C(max) (talinolol alone versus talinolol plus DLX) were 0.87(0.77-1.06), 0.85(0.74-1.01), 0.87 (0.68-1.12).

CONCLUSION

Our results suggest that DLX could inhibit the function of P-gp in vitro and in vivo, and caution should be exercised when DLX is to be co-administered with drugs that are P-gp substrate.

[Structure and activity of carvedilol]

Unique stereochemistry of the third-generation beta-adrenoblockers is a basis of advantages of the new drugs such as carvedilol. Data on the stereochemistry beta-adrenoblockers and the influence of their optical activity on the pharmacological effects of related drugs are presented. Main steps in the practical invest gation of carvedilol stereoisomers are reviewed. Clinical aspects of the use of carvedilol, representing a racemic mixture of two enantiomers, in the treatment chronic heart failure, arterial hypertension, and coronary heart disease are considered.

Transdermal delivery of carvedilol in rats: probing the percutaneous permeation enhancement mechanism of soybean extract-chitosan mixture

BACKGROUND

This study was designed for investigating the effect of soybean (SS) extract and chitosan (CTN) in facilitating the permeation of carvedilol (CDL) across rat epidermis.

METHOD

Transdermal flux of carvedilol through heat-separated rat epidermis was investigated in vitro using vertical Keshary-Chien diffusion cells. Biophysical and microscopic manifestations of epidermis treated with SS-extract, CTN, and SS extract-CTN mixture were investigated by using DSC, TEWL, SEM, and TEM. Biochemical estimations of cholesterol, sphingosine, and triglycerides were carried out for treated excised as well as viable rat epidermis. The antihypertensive activity of the patches in comparison to that after oral administration of carvedilol was studied in deoxycorticosterone acetate-induced hypertensive rats.

RESULTS

The solubility of CDL was found to be maximum in the presence of 1% (w/v) SS extract. The K(IPM/PB) of CDL decreased with increase in concentration of SS extract. The in vitro permeation of CDL across rat epidermis increased and was maximum with combination of SS extract and chitosan (CTN). Biochemical and microscopic studies revealed the initiation of reversal of barrier integrity after 12 hours. Furthermore, the application of patches containing SS extract-CTN mixture resulted in sustained release of carvedilol, which was able to control the hypertension in deoxycorticosterone acetate (DOCA) induced hypertensive rats through 24 hours. CTN was found to potentiate the permeation enhancing activity of SS extract.

CONCLUSION

The developed transdermal patches of CDL containing SS extract-CTN mixture exhibited better performance as compared to oral administration in controlling hypertension in rats.

Comparison of different pharmacodynamic models for pharmacokinetic-pharmacodynamic (PK-PD) modeling of carvedilol

The paper is aimed to investigate the pharmacokinetic (PK) and the pharmacodynamic (PD) properties of carvedilol using indirect response and effect-compartment link models, and compare the fitness of PK-PD models. Twenty male healthy Chinese volunteers received a single oral dose of 20 mg of carvedilol. The plasma concentrations of carvedilol were determined by reversed-phase HPLC method with fluorescence detection, and the pharmacokinetic parameters were calculated by DAS2.0. The mean arterial blood pressure was measured and the pharmacodynamics of carvedilol was characterized by tail-cuff manometry. The main pharmacokinetic parameters of carvedilol were as follows, t1/2 (4.56 +/- 2.56) h, Cmax (46.29 +/- 21.07) ng x mL(-1), AUC(0-infinity) (173.76 +/- 87.36) ng x mL(-1) x h. The estimated Kin was (0.41 +/- 0.31)% h(-1), Kout was (0.40 +/- 0.26) h(-1), the IC50 value was (24.40 +/- 21.10) ng x mL(-1) and the area under the effect curve (AUE) was (3.82 +/- 1.46)% h for the indirect response PD model. The Ke0 was (0.35 +/- 0.27) h(-1), the EC50 was (24.30 +/- 24.30) ng x mL(-1), and the AUE was (5.65 +/- 2.54)% h for the effect-compartment model. The HPLC method can be used for the pharmacokinetic study of carvedilol. The proposed effect-compartment link model provided more appropriate and better-fitting PK/PD characteristics than the indirect response model in Chinese healthy volunteers according to Akaike's information criterion values.

Is urethane-chloralose anaesthesia appropriate for pharmacokinetic-pharmacodynamic assessment? Studies with carvedilol

INTRODUCTION

The aim of the work was to establish the impact of urethane-chloralose anaesthesia on pharmacokinetic-pharmacodynamic (PK-PD) properties of carvedilol in control rats and L-NAME hypertensive animals.

METHODS

Male Wistar Rats were randomly divided into: control (n=12) with tap water to drink and L-NAME rats (n=12) with L-NAME solution (40 mg/kg/day) to drink for 2 weeks. Effects of carvedilol (1 mg kg(-1), i.v.) on blood pressure and heart rate were recorded during 3 h in conscious and urethane (500 mg kg(-1), i.p.) - chloralose (50 mg kg(-1), i.p.) anaesthetized rats. Carvedilol plasma pharmacokinetics was studied by means of traditional blood sampling. PK-PD modeling of carvedilol was made by means of an effect compartment model.

RESULTS

Neither urethane-chloralose nor L-NAME modified estimation of pharmacokinetic parameters of carvedilol. Although urethane-chloralose did not modify potency of carvedilol comparing with awake animals in control and hypertensive group, maximal negative chronotropic response was significantly greater in anaesthetized L-NAME rats in comparison to awake animals. Conversely, anaesthesia did not modify maximal chronotropic response to carvedilol in control rats. Whilst no differences were found in the estimated potency of carvedilol hypotensive response comparing control and L-NAME rats in both awake and anaesthetized conditions, maximal hypotensive effect of carvedilol was significantly greater in anaesthetized control and L-NAME animals in comparison to conscious rats. L-NAME rats showed a greater maximal hypotensive response comparing to control group.

DISCUSSION

Urethane-chloralose anaesthesia is an acceptable experimental condition for the evaluation of PK-PD properties of carvedilol, considering that it does not affect the potency of carvedilol for its chronotropic and hypotensive effect. Conclusions obtained from urethane-chloralose anaesthetized animals, regarding the impact of l-NAME treatment on PK-PD properties of carvedilol, did not differ from those obtained from conscious animals. Anaesthesia did not modify pharmacokinetic behaviour of carvedilol in both normotensive and L-NAME hypertensive rats.

Development of carvedilol transdermal patches: evaluation of physicochemical, ex vivo and mechanical properties

Monolithic matrix-type transdermal drug delivery systems for carvedilol were prepared using a film casting technique involving hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC), Eudragit RS 100 (ERS 100), and Eudragit RL 100 (ERL 100) as matrix-forming polymers. The prepared transdermal drug delivery systems were extensively evaluated for in vitro release, ex vivo permeation through rat abdominal skin, moisture absorption, moisture content, water vapor transmission, stability, and mechanical properties. Formulations F2, F3, and F5 were composed of a 4:1 ratio of HPMC, ERS 100; HPMC, HPC; and HPMC, ERL 100, respectively, whereas F4, F6, and F7 were composed of 3:0.5:0.5 of HPMC, ERS 100, HPC; HPMC, HPC, ERL 100; and HPMC, ERS 100, ERL 100. Formulation F1 was composed of HPMC polymer. All formulations carried 8% v/w of d-limonene as a penetration enhancer and 20% v/w of dibutylphthalate as a plasticizer. The physicochemical interaction between carvedilol and polymers were investigated by Fourier transform infrared spectroscopy and differential scanning calorimetry. Formulation F5 showed both maximum drug release (12.31 mg) and permeation (2987.67 microg/cm2) in 24 h, which differed significantly (P < 0.05) among all the formulations. Formulation F5 showed maximum flux (32.80 microg/h/cm2), which meets the flux requirements, and differed significantly (P < 0.05) among all the formulations with a permeation coefficient of 0.82 x 10(-2) cm/h. Fourier transform infrared spectroscopy and differential scanning calorimetry studies showed no evidence of interaction between the drug and polymers. The formulations mechanical properties, tensile strength and elastic modulus (5.89 kg/cm2 for formulation F5) reveal that they are strong but not brittle. A shelf life of 2 years was predicted for the transdermal drug delivery systems. Carvedilol monolithic matrix-type transdermal therapeutic systems could be prepared having both the required flux and suitable mechanical properties.

Investigations of a Novel Self-Emulsifying Osmotic Pump Tablet Containing Carvedilol

Carvedilol has been made into a novel osmotic pump tablet which includes Gelucire 44/14, Lutrol F68, Transcutol P, silicon dioxide, mannitol, citric acid, and sodium hydrogen carbonate. The Self-emulsifying osmotic pump tablet (SEOPT) has two outstanding features. It could improve the bioavailability of carvedilol by self-emulsifying drug delivery system (SEDDS), control the release rate and make the plasma concentrations more stable by elementary osmotic pump tablet. The results of transmission electron microscope (TEM) and particle size assessment showed that the shape of the resultant emulsion was round and regular, the average diameter of the particles was 246 nm. Since the solubility of carvedilol was improved by the emulsion, the elementary SEOPT could guarantee a complete release of carvedilol under the osmotic pressure of mannitol. The cumulative release at 12 hr was 85.18%. Therefore the disadvantage that lipophilic drugs can not be released completely when prepared into elementary osmotic pump tablet was resolved. The results of Differential scanning calorimetry (DSC), Infrared spectroscopy (IR) and X-ray diffraction diffraction (XRD) proved that carvedilol was amorphous in the preparation. The relative bioavailability of carvedilol in beagle dogs was 156.78%. The plasma concentrations were more stable compared with that of commercially available tablet (Luode). And the in vitro and in vivo correlation was good (r = 0.9725). Therefore, the elementary SEOPT developed in this paper might provide a new idea for preparing lipophilic drugs into osmotic pump tablet conveniently.

Preparation and Evaluation of SEDDS and SMEDDS Containing Carvedilol

A new self-emulsifying drug delivery system (SEDDS) and self-microemulsifying drug delivery system (SMEDDS) have been developed to increase the solubility, dissolution rate, and, ultimately, oral bioavailability of a poorly water soluble drug, carvedilol. Ternary phase diagrams were used to evaluate the self-emulsification and self-microemulsfication domains. The self-emulsification time following introduction into an aqueous medium under gentle agitation was evaluated. The minimum self-emulsification time was found at a Tween 80 content of 40%. The particle size distribution and zeta-potential were determined. Benzoic acid had a dual function, it improved the self-emulsification performance of SEDDS and SMEDDS in 0.1 N HCl and lead to a positively charged emulsion. The in vitro dissolution rate of carvedilol from SEDDS and SMEDDS was more than two-fold faster compared with that from tablets. The developed SEDDS formulations significantly improved the oral bioavailability of carvedilol significantly, and the relative oral bioavailability of SEDDS compared with commercially available tablets was 413%.

Development of Novel Interpenetrating Network Gellan Gum-Poly(vinyl alcohol) Hydrogel Microspheres for the Controlled Release of Carvedilol

Novel interpenetrating polymeric network microspheres of gellan gum and poly(vinyl alcohol) were prepared by the emulsion cross-linking method. Carvedilol, an antihypertensive drug, was successfully loaded into these microspheres prepared by changing the experimental variables such as ratio of gellan gum:poly(vinyl alcohol) and extent of cross-linking in order to optimize the process variables on drug encapsulation efficiency, release rates, size, and morphology of the microspheres. Formation of interpenetrating network and the chemical stability of carvedilol after preparing the microspheres was confirmed by Fourier transform infrared spectroscopy. Differential scanning calorimetry and x-ray diffraction studies were made on the drug-loaded microspheres to investigate the crystalline nature of the drug after encapsulation. Results indicated a crystalline dispersion of carvedilol in the polymer matrix. Scanning electron microscopy confirmed the spherical nature and smooth surface morphology of the microspheres produced. Mean particle size of the microspheres as measured by laser light scattering technique ranged between 230 and 346 microm. Carvedilol was successfully encapsulated up to 87% in the polymeric matrices. In vitro release studies were performed in the simulated gastric fluid or simulated intestinal fluid. The release of carvedilol was continued up to 12 h. Dynamic swelling studies were performed in the simulated gastric fluid or simulated intestinal fluid, and diffusion coefficients were calculated by considering the spherical geometry of the matrices. The release data were fitted to an empirical relation to estimate the transport parameters. The mechanical properties of interpenetrating polymeric networks prepared were investigated. Network parameters such as molar mass between cross-links and cross-linking density for interpenetrating polymeric networks were calculated.

In vitro permeation of carvedilol through porcine skin: effect of vehicles and penetration enhancers

This investigation studied the effect of vehicles on the in vitro permeation of carvedilol from saturated solutions across porcine skin and selected appropriate penetration enhancers. Labrasol, Transcutol, polyethylene glycol 400, propylene glycol, ethanol, oleic acid, isopropyl myristate, and phosphate buffered saline (pH 7.4) containing 40% v/v polyethylene glycol 400 as control, were used as vehicles; limonene, carvone, camphor, menthol, Transcutol, and Labrasol at 5% w/v concentrations were used as penetration enhancers. Skin permeation studies were conducted in Franz diffusion cells using excised porcine ear skin. Solubility was highest (369.13 mg/mL) in Transcutol, whereas isopropyl myristate showed the lowest solubility (0.79 mg/mL) among all the vehicles. The flux of carvedilol from Transcutol, Labrasol, polyethylene glycol 400, ethanol, and oleic acid was 10.5, 8.6, 4.2, 2.9, and 1.5 times higher, respectively, than that observed with control. The flux obtained using Transcutol was significantly higher (P < 0.05) than the flux obtained using the other vehicles. However, the flux values of carvedilol using isopropyl myristate (P < 0.01) and propylene glycol (P < 0.05) were significantly lower than that of the control. Solutions containing 5% w/v camphor showed maximum permeation (232.54 microg) in 24 h with a flux of 3.19 microg/cm2/h, which was significantly different (P < 0.05) than the flux obtained using other permeation enhancers. The control sample showed lowest permeation (30.50 microg), with a flux of 0.33 microg/cm2/h. The flux of carvedilol from the solutions containing 5% w/v camphor, limonene, Transcutol, carvone, Labrasol, and menthol were 9.7, 7.6, 7.6, 6.3, 4.7, and 2.3 times higher, respectively, than that observed using the control. The present study suggests that Transcutol, Labrasol, and polyethylene glycol 400 may be used as potential vehicles and camphor, limonene, and Transcutol at a 5% w/v level as penetration enhancers.

Design and in vivo evaluation of carvedilol buccal mucoadhesive patches

The buccal region offers an attractive route of administration for systemic drug delivery. Carvedilol (dose, 3.125-25 mg) is beta-adrenergic antagonist. Its oral bioavailability is 25-35% because of first pass metabolism. Buccal absorption studies of a carvedilol solution in human volunteers showed 32.86% drug absorption. FTIR and UV spectroscopic methods revealed that there was no interaction between carvedilol and polymers. Carvedilol patches were prepared using HPMC, carbopol 934, eudragit RS 100, and ethylcellulose. The patches were evaluated for their thickness uniformity, folding endurance, weight uniformity, content uniformity, swelling behaviour, tensile strength, and surface pH. In vitro release studies were conducted for carvedilol-loaded patches in phosphate buffer (pH, 6.6) solution. Patches exhibited drug release in the range of 86.26 to 98.32% in 90 min. Data of in vitro release from patches were fit to different equations and kinetic models to explain release profiles. Kinetic models used were zero and first-order equations, Hixon-Crowell, Higuchi, and Korsmeyer-Peppas models. In vivo drug release studies in rabbits showed 90.85% of drug release from HPMC-carbopol patch while it was 74.63 to 88.02% within 90 min in human volunteers. Good correlation among in vitro release and in vivo release of carvedilol was observed.

Pharmacological washout for the correct evaluation of the head-up tilt testing

Head-up tilt testing is an important tool in the diagnosis of syncope. Several different protocols are in use. We describe the case of a 70-year-old Italian woman admitted to our observation. The patient was in antihypertensive treatment with carvedilol and with a combination of lisinopril and hydrochlorothiazide. A simplified Italian protocol head-up tilt testing was performed. A 4.10 s pause with syncope and a profound hypotension (blood pressure values were 65/50 mm Hg) were observed after 3 min in the provocation phase. Second-degree atrioventricular Block of the 2:1 form, advanced second-degree atrioventricular block and junctional escape rhythm (28 bpm) were observed. A simplified Italian protocol head-up tilt testing was performed after 40 days of withdrawal of carvedilol. A 2 s pause with presyncope and a hypotension (blood pressure values were 80/70 mm Hg) were observed after 2 min in the provocation phase. ECG revealed a bradycardic sinusal rhythm with heart rate of 42 bpm. This case assesses the importance of a pharmacological washout for the correct evaluation of the head-up tilt testing.

Effect of grapefruit juice, naringin, naringenin, and bergamottin on the intestinal carrier-mediated transport of talinolol in rats

The effect of two varieties of grapefruit juice (white and ruby red) and its selected components (naringin, naringenin, and bergamottin) was investigated on the activity of the P-glycoprotein (P-gp) in male Sprague-Dawley rats. Talinolol, a nonmetabolized P-gp substrate, was used as a marker compound. The white grapefruit juice (GFJ) had a minor effect on talinolol pharmacokinetics, but the ruby red GFJ reduced the C max and the AUC (0-infinity) by 60% and 50% of the control, respectively. However, among the GFJ constituents tested, bergamottin (0.22 mg/kg) was the most potent component augmenting the C max and the AUC (0-infinity) of talinolol by 2.4- and 1.8-fold, respectively, if compared to the control group. The flavonoids naringenin (0.7 mg/kg) and naringin (2.4 and 9.4 mg/kg) had a similar effect increasing the talinolol C max and AUC (0-infinity) by 1.5- to 1.8-fold, respectively. In conclusion, the effect of GFJ on P-gp activity seems to depend on the variety, the concentration of compounds in the juice, and the composition of different ingredients.

Nanoemulsion system for the transdermal delivery of a poorly soluble cardiovascular drug

The purpose of the present study is to develop and evaluate the potential of nanoemulsions for increasing the solubility and the in vitro transdermal delivery of carvedilol. Pseudoternary phase diagrams were developed and various nanoemulsion formulations were prepared using oleic acid and isopropyl myristate (IPM) (1:1) as the oil, Tween 80 as surfactant, and Transcutol P as cosurfactant. The prepared nanoemulsions were subjected to physical stability tests. Transdermal permeation of carvedilol through rat abdominal skin was determined with Keshary-Chien diffusion cell. Significant increase (P < 0.05) in the steady state flux (Jss) and permeability coefficient (Kp) was observed in nanoemulsion formulations as compared to control or drug-loaded neat components. The highest value of these permeability parameters was obtained in optimized formulation B3, which consisted of 0.5% w/w of carvedilol, 6% w/w of oleic acid:IPM (1:1), 22.5% w/w of Tween 80, 22.5% w/w of Transcutol P, and 49% w/w of distilled water and in which the solubility of the drug was 4500-fold higher. The optimized nanoemulsion was characterized for pH, conductivity, viscosity, droplet size, droplet shape, and refractive index. Thermodynamic studies showed that there had been a significant decrease of 88% in activation energy (Eact) when the drug was incorporated in nanoemulsion. The irritation studies suggested that the optimized nanoemulsion was a non-irritant transdermal delivery system.

[Responses of hemodynamics and splanchnic organ blood flow to esmolol during inhalation of volatile anesthetics in dogs]

BACKGROUND

Because the hemodynamic alterations due to sympathetic suppression by the interaction of esmolol with volatile anesthetics may alter the blood flow to the splanchnic organs, this study was designed to investigate whether esmolol might modify the hemodynamics and splanchnic organ blood flow in anesthetized dogs.

METHODS

Anesthesia was maintained with 0.9% halothane, 1.3% isoflurane or 2.4% sevoflurane (1MAC, n=8, each) in oxygen. Esmolol was infused at a constant rate of 400 microg * kg(-1) x min(-1) during a 60 min-infusion period. The renal, hepatic, and pancreatic blood flows (RBF, HBF, and PBF) were measured by using the hydrogen clearance method.

RESULTS

Mean arterial pressure in all three groups decreased without any changes in heart rate or systemic vascular resistance. Cardiac index in all three groups decreased with reductions in cardiac contractility. The RBF, HBF, and PBF in all three groups were reduced during the esmolol infusion.

CONCLUSIONS

The splanchnic organ blood flow reductions caused by esmolol may be due to cardiac depression, whereas there appears to be no differences in there change regarding the kind of the volatile anesthetics. These findings suggest that hypotension induced by esmolol may impair the maintenance of splanchnic organ blood flow during anesthesia by volatile agents.

Pharmacokinetics and bioavailability of diisopropanolamine (DIPA) in rats following intravenous or dermal application

This study was conducted to determine the relative dermal bioavailability (absorption), distribution, metabolism, and excretion (ADME) of diisopropanolamine (DIPA), an alcohol amine used in a number of industrial and personal care products. Groups of 4 female Fischer 344 rats received either a single bolus i.v. dose of 19.0mg/kg (14)C-DIPA in water or a dermal application of 19.5mg/kg (14)C-DIPA in acetone to an area of 1cm(2) on the back and covered with a bandage. Time-course blood and excreta were collected and radioactivity determined. Urine was analyzed for DIPA and monoisopropanolamine (MIPA). Following i.v. administration, DIPA was rapidly cleared from the plasma and excreted into urine in a biexponential manner (t(1/2alpha), 0.4h; t(1/2beta), 2.9h). The levels of radioactivity in plasma dropped below the limit of detection 12h post-dosing. A total of 97+/-4% of the dose was actively excreted in urine by kidney, most ( approximately 71%) within 6h of dosing, virtually all as parent compound; renal clearance exceeded the glomerular filtration rate. Following dermal application, approximately 20% of the dose was absorbed in 48 h with the steady-state penetration rate of approximately 0.2%/h. Most (14.4%) of the applied radioactivity was excreted in urine at a relatively constant rate due to the presence of large amount of the (14)C-DIPA at the application site. Fecal elimination was <0.2% of the dose. The absorbed DIPA did not accumulate in tissues; only approximately 0.1% of the administered dose was found in liver and kidney. The absolute systemic dermal bioavailability (dose corrected AUC(dermal)/AUC(i.v.)) of (14)C-DIPA was 12%. The ADME of DIPA contrasts that of its diethanol analogue, diethanolamine, which displays a broad spectrum of toxicity in rats and mice. Toxicologically significant concentrations of DIPA are unlikely to be achieved in the systemic circulation and/or tissues as a result of repeated dermal application of products containing DIPA due to slow absorption from the skin, rapid unchanged elimination in urine, and majority of the products contain <or= 1% DIPA.

Estimation of carvedilol in human plasma by using HPLC-fluorescence detector and its application to pharmacokinetic study

A simple, precise and sensitive high performance liquid chromatography procedure has been developed for determination of carvedilol in human plasma. The method was developed on Lichrosphere R CN column using a mobile phase of acetonitrile/20 mM ammonium acetate buffer with 0.1% triethylamine (pH adjusted to 4.5) (40/60, v/v). The peaks were detected by using fluorescence detector (excitation wavelength 282 nm and emission wavelength 340 nm). Carvedilol and domperidone (internal standard) were extracted by liquid-liquid extraction procedure using dichloromethane. This method was specific and had a linearity range of 1-128 ng/ml with intra- and inter-day precision (%C.V.) less than 15%. The accuracy ranges from 87.3 to 100.88% and the recovery of carvedilol was 69.90%. The stability studies showed that carvedilol in human plasma was stable during short-term period for sample preparation and analysis. This method was used to assay the carvedilol in human plasma samples obtained from subjects who had been given an oral tablet of 12.5 mg carvedilol.

Are [O-methyl-11C]derivatives of ICI 89,406 beta1-adrenoceptor selective radioligands suitable for PET?

PURPOSE

Radioligand binding studies show that beta(1)-adrenoceptor (beta(1)-AR) density may be reduced in heart disease without down regulation of beta(2)-ARs. Radioligands are available for measuring total beta-AR density non-invasively with clinical positron emission tomography (PET) but none are selective for beta(1)- or beta(2)-ARs. The aim was to evaluate ICI 89,406, a beta(1)-AR-selective antagonist amenable to labelling with positron emitters, for PET.

METHODS

The S-enantiomer of an [O-methyl-(11)C] derivative of ICI 89,406 ((S)-[(11)C]ICI-OMe) was synthesised. Tissue radioactivity after i.v. injection of (S)-[(11)C]ICI-OMe (< 2 nmol x kg(-1)) into adult Wistar rats was assessed by small animal PET and post mortem dissection. Metabolism was assessed by HPLC of extracts prepared from plasma and tissues and by measuring [(11)C]CO(2) in exhaled air.

RESULTS

The heart was visualised by PET after injection of (S)-[(11)C]ICI-OMe but neither unlabelled (S)-ICI-OMe nor propranolol (non-selective beta-AR antagonist) injected 15 min after (S)-[(11)C]ICI-OMe affected myocardial radioactivity. Ex vivo dissection showed that injecting unlabelled (S)-ICI-OMe, propranolol or CGP 20712A (beta(1)-selective AR antagonist) at high dose (> 2 mumol x kg(-1)) before (S)-[(11)C]ICI-OMe had a small effect on myocardial radioactivity. HPLC demonstrated that radioactivity in myocardium was due to unmetabolised (S)-[(11)C]ICI-OMe although (11)C-labelled metabolites rapidly appeared in plasma and liver and [(11)C]CO(2) was detected in exhaled air.

CONCLUSION

Myocardial uptake of (S)-[(11)C]ICI-OMe after i.v. injection was low, possibly due to rapid metabolism in other tissues. Injection of unlabelled ligand or beta-AR antagonists had little effect indicating that binding was mainly to non-specific myocardial sites, thus precluding the use of (S)-[(11)C]ICI-OMe to assess beta(1)-ARs with PET.

Determination of bevantolol in human plasma by high performance liquid chromatography using solid phase extraction technique

A method was developed and fully validated for the determination of bevantolol, an adrenergic-receptor blocker, in human plasma. Bevantolol and betaxolol as internal standard (I.S) were extracted from 1 mL of human plasma by solid phase extraction technique using Sep-pak silica cartridge. Chromatographic separation was accomplished under isocratic conditions using a reverse-phase C8 analytical column and mixture of dibasic ammonium phosphate (pH 5.7; 50 mM)-acetonitrile (75:25, v/v) as mobile phase, with a detection wavelength at 220 nm. The method was proved to be specific by testing six different human plasma sources. Linearity was established for the concentration ranges of 40-1600 ng/mL with correlation coefficent of 0.9995. The lower limit of quantification 40 ng/mL with precision of 10.9% as C.V%.

Evaluation of effects of polymorphism for metabolic enzymes on pharmacokinetics of carvedilol by population pharmacokinetic analysis

In our previous study it was observed that the frequencies of UGT1A1*6, UGT2B7*3 and CYP2D6*10 in patients who have a low level ability of glucuronidation were significantly higher than those in patients with a high level of ability of glucuronidation. The same tendency was found in the frequency of CYP2D6*5, though there was no significant difference. The purpose of this study was to evaluate the effects of the polymorphism on pharmacokinetics of carvedilol by population pharmacokinetic analysis. Population pharmacokinetic analysis was performed using 373 plasma concentrations from 41 patients with chronic heart failure or angina pectoris. A one compartment pharmacokinetic model with first-order absorption (for oral dosing) was used to describe the concentration-versus-time data for carvedilol. We examined the effects of various clinical and genetic covariables in the regression models for clearance and volume of distribution. The results suggested that the factors of interindividual variation for carvedilol clearance were creatinine clearance and polymorphisms of UGT2B7 and CYP2D6 in the Japanese population with heart disease. It was estimated that UGT2B7*3 decreased the clearance of carvedilol by 37%, but UGT2B7*2 did not show any effect. Clearance in the patients who have intermediate activity of CYP2D6 was decreased by 39%.

Symptom-driven lorazepam protocol for treatment of severe alcohol withdrawal delirium in the intensive care unit

STUDY OBJECTIVE

To compare outcomes of treating alcohol withdrawal delirium (AWD) with a symptom-driven benzodiazepine protocol versus nonprotocol benzodiazepine infusions in the intensive care unit (ICU).

DESIGN

Retrospective observational study of a quality improvement project.

SETTING

Medical intensive care unit at a Veterans Affairs medical center.

PATIENTS

Thirty-six patients who had 40 ICU admissions for AWD between January 1, 1994, and May 31, 2003. Sixteen episodes (15 patients [historical controls]) occurred before implementation of the symptom-driven protocol in 1998, and 24 episodes (21 patients) occurred after implementation.

MEASUREMENTS AND MAIN RESULTS

Outcomes evaluated were time to reach symptom control, total dose of benzodiazepine, amount of time receiving continuous benzodiazepine infusion, length of ICU and hospital stay, polypharmacy (use of multiple benzodiazepines), and complications of treatment. The historical control group was treated according to physician preference, which consisted of continuous-infusion midazolam without a protocol. The symptom-driven protocol used lorazepam administered initially as intermittent intravenous doses, progressing to a continuous intravenous infusion according to a locally developed symptom scale. The mean +/- SD values for the outcomes in the historical control group versus the protocol group were as follows: time to control symptoms 19.4 +/- 9.7 versus 7.7 +/- 4.9 hours (p=0.002), cumulative benzodiazepine dose in lorazepam equivalents 1677 +/- 937 versus 1044 +/- 534 mg (p=0.014), time receiving benzodiazepine continuous infusion 122.1 +/- 64.4 versus 52.0 +/- 35.1 hours (p=0.001), length of stay in the ICU 7.7 +/- 6.3 versus 5.6 +/- 1.7 days (p=0.21), and length of hospital stay 15.3 +/- 8.9 versus 11.2 +/- 3.4 days (p=0.43).

CONCLUSIONS

Use of a symptom-driven protocol was associated with significantly decreased time to symptom control, amount of sedative required, and time spent receiving benzodiazepine infusion compared with historical controls. The use of the protocol is effective but requires close monitoring to ensure protocol compliance and to avoid potential propylene glycol toxicity.

Population pharmacokinetics of S(-)-carvedilol in healthy volunteers after administration of the immediate-release (IR) and the new controlled-release (CR) dosage forms of the racemate

Carvedilol is a beta(1)-, beta(2)-, and alpha(1)-adrenoreceptor blocker indicated for treatment of hypertension and mild-to-severe congestive heart failure. The objective of this study was to develop and evaluate a single population model that describes S(-)-carvedilol pharmacokinetics from both the immediate-release (IR) and the new controlled-release dosage forms of the racemate. Carvedilol IR data (1270 measurements) were obtained from 2 open-label studies (50 mg/25 mg Q12 hours for 2 doses). Carvedilol CR data (2058 measurements) were obtained from an open-label, nonrandomized, dose-rising (10, 20, 40, and 80 mg), 4-period balanced crossover study. All data were simultaneously analyzed using NONMEM V. Leverage analysis and internal evaluations were conducted for the final model. A 2-compartment model with first-order absorption and elimination provided the best fit. The model included different absorption rates (KAs) for the CR and IR morning (IR(AM)) and evening (IR(PM)) doses; incorporating change-points at certain times. Estimates of KAs indicated that the absorption was slower at equivalent times and extended for CR relative to IR carvedilol. Oral clearance of S(-)-carvedilol was 149 L/h. The IR(PM) and the CR doses had bioavailability (F(rel)) of 0.80 and 0.76, respectively, relative to the IR(AM) dose. The inter-subject variability in KAs was lower for the CR dosage form than the original IR dosage form. Estimation of interoccasion variability on KAs and F(rel) for the CR dosage form improved the fit. The model performed well in simulation and leverage analysis indicated its robustness. The model will be a useful tool for future simulation studies.

Single quadrupole mass spectrometry for pre-clinical pharmacokinetic analysis: Quantitation of carvedilol in dog plasma

The pharmaceutical industry standard for bioanalysis is LC/MS/MS. There are, however, many instances where a single quadrupole detector could successfully be used to provide adequate sensitivity and selectivity for quantitation of drug substances in biological matrices. This paper presents one example of how a single quadrupole detector can be employed in a sensitive and selective analytical method for quantitation of carvedilol. A Synergi Hydro-RP (50 mm x 2 mm i.d.; 4 microm) column was used with acetonitile:water:formic acid mobile phase (32:68:0.01, v/v) at a flow rate of 200 microL/min into a single quadrupole mass spectrometer with an electrospray interface in the positive SIM mode. Using a 300 microL plasma aliquot and a liquid-liquid extraction procedure the limit of quantitation for the assay was 1 ng/mL. The assay utility was demonstrated in the analysis of carvedilol pharmacokinetic profiles in beagle dogs following oral carvedilol administration.

Development and evaluation of carvedilol transdermal patches

Transdermal patches of carvedilol with a HPMC-drug reservoir were prepared by the solvent evaporation technique. In this investigation, the membranes of Eudragit RL100 and Eudragit RS100 were cast to achieve controlled release of the drug. The prepared patches possessed satisfactory physicochemical characteristics. Thickness, mass and drug content were uniform in prepared batches. Moisture vapour transmission through the patches followed zero-order kinetics. In vitro permeation studies were performed using a K-C diffusion cell across hairless guinea pig skin and followed the super case II transport mechanism. The effects of non-ionic surfactants Tween 80 and Span 80 on drug permeation were studied. The nonionic surfactants in the patches increased the permeation rate, Span 80 exhibiting better enhancement relative to Tween 80. The patches were seemingly free of potentially hazardous skin irritation.

Development and in vitro evaluation of buccoadhesive carvedilol tablets

Buccoadhesive tablets of carvedilol were prepared using HPMC K4M, HPMC K15M and Carbopol 934 as mucoadhesive polymers. Fifteen formulations were developed with varying concentrations of polymers. Formulations of the BC or BD series were composed of HPMC K4M or HPMC K15M in ratios of 1:1 to 1:5 whereas in the BE series Carbopol 934 was used (1:0.25 to 1:1.50). The formulations were tested for in vitro drug release, in vitro bioadhesion, moisture absorption and in vitro drug permeation through porcine buccal mucosa. Formulation BC3 showed maximum release of the drug (88.7 +/- 0.4%) with the Higuchi model release profile and permeated 21.5 +/- 2.9% of the drug (flux 8.35 +/- 0.291 microg h(-1)cm(-2)) permeation coefficient 1.34 +/- 0.05 cm h(-1)) through porcine buccal membrane. BC3 formulation showed 1.62 +/- 0.15 N of peak detachment force and 0.24 +/- 0.11 mJ of work of adhesion. FTIR results showed no evidence of interaction between the drug and polymers. XRD study revealed that the drug is in crystalline form in the polymer matrix. The results indicate that suitable bioadhesive buccal tablets with desired permeability could be prepared.

Achiral–chiral LC/LC–FLD coupling for determination of carvedilol in plasma samples for bioequivalence purposes

Bioequivalence data for two pharmaceutical formulations (solid oral dosage forms) containing carvedilol is presented for both racemic and enantiomers of the active substance. This was achieved by on-line coupling of two liquid chromatographic separations followed by fluorescence detection. The first LC dimension was used for a fast separation of racemic carvedilol from propranolol (IS) and the endogenous matrix, by means of a reversed phase mechanism. The peak of racemic carvedilol was on-line transferred to the second enantioselective LC dimension, based on a reversed phase separation on cellulose tris(3,5-dimethyl-phenylcarbamate) stationary phase. Both stages were monitored over a single run by means of a fluorescence detector operated at an excitation wavelength of 285 nm and an emission wavelength of 355 nm. Automated shortcutting of the racemic carvedilol peak to the chiral column and simultaneous detection over the two LC dimensions have been obtained by using an experimental set-up based on two six-port rotative switching valves. Linearity was demonstrated on the interval 2-150 ng/mL for racemic carvedilol and on 1-75 ng/mL intervals for enantiomers. LLOQ fits between 0.7 and 1.4 ng/mL. Recoveries of the target compounds are 87+/-4 and 81+/-4% for the IS. Precision ranged from 0.6 to 2.5% and the mean accuracy obtained on quality control samples (measured as % bias) over the whole study falls between -0.8 and 6.3%.

Quantification of carvedilol in human plasma by liquid chromatography using fluorescence detection: Application in pharmacokinetic studies

A simple, rapid and sensitive isocratic reversed-phase HPLC method with fluorescence detection using a monolithic column has been developed and validated for the determination of carvedilol in human plasma. The separation was performed on a Chromolith Performance (RP-18e, 100mm x 4.6mm) column with an isocratic mobile phase consisting of 0.01 M disodium hydrogen phosphate buffer-acetonitrile (40:60, v/v) adjusted to pH 3.5. The sample preparation involves protein precipitation procedure and analytical recovery was complete. Letrozole was used as internal standard. The assay enables the measurement of carvedilol for therapeutic drug monitoring with a minimum quantification limit (LOQ) of 1 ng ml(-1). The excitation and emission wavelengths were set at 240 and 340 nm, respectively. The calibration curve was linear over the concentration range 1-80 ng ml(-1). The coefficients of variation for inter-day and intra-day assay were found to be less than 8.0%.

Unexpected effect of concomitantly administered curcumin on the pharmacokinetics of talinolol in healthy Chinese volunteers

OBJECTIVE

To investigate the effect of concomitantly administered curcumin on the pharmacokinetics of the beta1 adrenoceptor blocker talinolol.

METHODS

The study was conducted in a self-controlled, two-period experiment with a randomized, open-labeled design, using 12 healthy volunteers and a wash out period of 1 week between the administration of a single oral dose of 50 mg talinolol and the concomitant administration of curcumin (300 mg day(-1) for 6 days) and a single oral dose of 50 mg talinolol on the seventh day. Concentrations of talinolol were measured in plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry. Non-compartmental analysis was used to characterize talinolol plasma concentration-time profiles, all pharmacokinetic parameters were calculated using DAS: (ver. 2.0) software, and comparisons of mean values were analyzed by the Wilcoxon signed rank test. Differences were considered to be significant at p < 0.05 (two-sided test).

RESULTS

The consumption of curcumin for 6 days reduced the area under the curve (AUC) from predose to infinity (AUC(0-infinity)) of talinolol from 1860.0 +/- 377.9 to 1246.0 +/- 328.2 ng x h mL(-1), the highest observed concentration values (C(max)) were significantly decreased from 147.8 +/- 63.8 to 106.4 +/- 39.9 ng mL(-1), and the CL/F was increased from 27.9 +/- 5.5 to 43.1 +/- 13.4 L x h(-1) (p < 0.05). There was no significant difference in sampling time for C(max) (t(max)) and elimination half-life (t(1/2)) values between the two periods (p > 0.05). The interindividual variability in AUC(0-60) and C(max) of talinolol was comparable in two study periods; the coefficient of variance (CV) of AUC(0-60) and C(max) was 26 and 40% after curcumin versus 21 and 43% after talinolol alone, respectively.

CONCLUSION

We suggest that the reduced bioavailability of talinolol is most probably due to the low intraluminal curcumin concentration, or possibly due to the upregulation of further ATP-binding cassette transporters, such as MRP2, in different tissues.

Application of liquid chromatography-tandem mass spectrometry method for the analysis of new nonselective beta-adrenergic blocker 1-(1-H-indol-4-yloxy)-3-{[2-(2-methoxy phenoxy)ethylo]amino}propan-2-ol (2F109) in rat plasma

A sensitive and specific liquid chromatography electrospray ionization-tandem mass spectrometry method for the enantioselective determination of the novel beta-adrenolytic compound, 1-(1-H-indol-4-yloxy)-3-{[2-(2-methoxyphenoxy)ethylo]amino} propan-2-ol, in rat plasma has been developed and validated. Chromatography was performed on a reversed-phase Chiralcel OD-RH analytical column (150x4.6 mm, 5 microm, Daicel Chemical Industries, Tokyo, Japan) with isocratic elution using a mobile phase containing acetonitrile and water with 0.01% formic acid. Detection was achieved by an Applied Biosystems MDS Sciex (Concord, Ontario, Canada) API 2000 triple quadrupole mass spectrometer. Electrospray ionization (ESI) was used for ion production. The limit of detection in the MRM mode was found to be 1.25 ng/ml. The limit of quantification of both enantiomers was 2.5 ng/ml. The precision and accuracy for both intra- and inter-day determination of 2F109 enantiomers ranged from 2.6 to 12% and from 89.1 to 107.1%. This analytical method allowed us to carry out pharmacokinetic studies in rats. Our findings demonstrate that 2F109 shows stereoselective disposition in rat plasma after i.v. administration. The terminal half-lives of (+)-(R)-2F109 and (-)-(S)-2F109 were 33.5 and 42.6 min, respectively. The AUC0-inf of (+)-(R)-2F109 exceeded that of (-)-(S)-2F109.

Determination of talinolol in human plasma by high performance liquid chromatography-electrospray ionization mass spectrometry: application to pharmacokinetic study

A rapid and sensitive method for determination and screening in human plasma of talinolol is described using propranolol as the internal standard. The analytes in plasma were extracted by liquid-liquid extraction using methyl t-butyl ether. After removed and dried the upper organic phase, the extracts were reconstituted with a fixed volume of buffer of ammonium acetate and acetonitrile (60:40, v/v). The extracts were analyzed by a HPLC coupled to electrospray ionization mass spectrometry (HPLC-MS/ESI). The HPLC separation of the analytes was performed on a Phenomenex C18 (250 mmx4.6 mm, 5 microm, USA) column, with a flow rate of 0.85 mL/min. The complete elution was obtained within 5.5 min. The calibration curve was linear in the 1.0-400.0 ng/mL range for talinolol, with a coefficient of determination of 0.9996. The average extraction recovery was above 83%. The methodology recovery was between 101% and 102%. The limit of detection (LOD) was 0.3 ng/mL for talinolol. The intraday and inter-day coefficients of variation were less than 6%. This HPLC-MS/ESI procedure was used to assess the pharmacokinetics of talinolol. A single oral 50 mg dose of talinolol tablet was administered to 12 healthy Chinese volunteers, the main pharmacokinetic data are as follows: Cmax was 147.8+/-63.8 ng/mL; tmax was 2.0+/-0.7 h; t1/2 was 12.0+/-2.6 h. The method is accurate, sensitive and simple for the pharmacokinetic study of talinolol.

Induction of intestinal P-glycoprotein by St John's wort reduces the oral bioavailability of talinolol

St John's wort (SJW) is known to induce cytochrome P450 (CYP) 3A4 and P-glycoprotein through pregnane X-receptor activation. Our study evaluated the effects of long-term SJW administration on oral and intravenous pharmacokinetics of the nonmetabolized in vivo probe of P-glycoprotein, talinolol, in relation to intestinal P-glycoprotein expression. In a controlled, randomized study (N=9), the pharmacokinetics of oral (50 mg) and intravenous talinolol (30 mg) was determined before and after 12 days SJW (900 mg daily, Jarsin 300). Duodenal biopsies were taken and MDR1 genotypes assessed. SJW reduced the oral talinolol bioavailability by 25% (P=0.049) compared with water control. A 93% increase in oral clearance (P=0.177) and a 31% reduction in area under the serum concentration time curve (AUC; P=0.030) were observed. Renal and nonrenal clearance (CLNR), elimination half-life, peak serum drug concentration (Cmax), and time to reach Cmax were not significantly altered. After intravenous talinolol, SJW affected only CLNR (35% increase compared with water, P=0.006). SJW increased MDR1 messenger ribonucleic acid (mRNA) as well as P-glycoprotein levels in the duodenal mucosa. Subjects with the combined MDR1 genotype comprising 1236C>T, 2677G>T/A, and 3435C>T polymorphisms had lower intestinal MDR1 mRNA levels and displayed an attenuated inductive response to SJW as assessed by talinolol disposition. Long-term SJW decreased talinolol AUC with a corresponding increase in intestinal MDR1 expression, suggesting that SJW has a major inductive effect on intestinal P-glycoprotein. Interestingly, the magnitude of induction appeared to be affected by MDR1 genotype.