Therapeutic drug monitoring: antiarrhythmic drugs

Acute and Sub-Chronic Intraperitoneal Toxicity Studies of the Elsholtzia ciliata Herbal Extract in Balb/c Mice

Elsholtzia ciliata essential oil (E. ciliata) has been reported to have an impact on the cardiovascular system. However, its toxicity remains unknown. Therefore, the objective of this investigation was to evaluate the toxicological aspects of the E. ciliata extract. Male Balb/c mice were subjected to either acute (a single dose administered for 24 h) or sub-chronic (daily dose for 60 days) intraperitoneal injections of the E. ciliata extract. The mice were assessed for blood hematological/biochemical profiles, mitochondrial functions, and histopathological changes. Additionally, in vitro cytotoxicity assessments of the E. ciliata extract were performed on immobilized primate kidney cells (MARC-145, Vero) and rat liver cells (WBF344) to evaluate cell viability. The control groups received an equivalent volume of olive oil or saline. Our results demonstrated no significant detrimental effects on hematological and biochemical parameters, mitochondrial functions, cellular cytotoxicity, or pathological alterations in vital organs following the intraperitoneal administration of the E. ciliata extract over the 60-day sub-chronic toxicity study. In general, E. ciliata displayed no indications of toxicity, suggesting that the E. ciliata extract is a safe natural product with a well-defined therapeutic and protective index (found to be 90 and 54, respectively) in Balb/c mice.

Natural products as the calcium channel blockers for the treatment of arrhythmia: Advance and prospect

Arrhythmia is one of the commonly heart diseases with observed abnormal heart-beat rhythm that caused by the obstacles of cardiac activity and conduction. The arrhythmic pathogenesis is complex and capricious and related with other cardiovascular diseases that may lead to heart failure and sudden death. In particular, calcium overload is recognized as the main reason causing arrhythmia through inducing apoptosis in cardiomyocytes. Moreover, calcium channel blockers have been widely used as the routine drugs for the treatment of arrhythmia, but the different arrhythmic complications and adverse effects limit their further applications and demand new drug discovery. Natural products have always been the rich minerals for the development of new drugs that could be employed as the versatile player for the discovery of safe and effective anti-arrhythmia drugs with new mechanisms. In this review, we summarized natural products with the activity against calcium signaling and the relevant mechanism of actions. We are expected to provide an inspiration for the pharmaceutical chemists to develop more potent calcium channel blockers for the treatment of arrhythmia.

Electrochemically driven optical and SERS immunosensor for the detection of a therapeutic cardiac drug

Cardiovascular diseases pose a serious health risk and have a high mortality rate of 31% worldwide. Digoxin is the most commonly prescribed pharmaceutical preparation to cardiovascular patients particularly in developing countries. The effectiveness of the drug critically depends on its presence in the therapeutic range (0.8–2.0 ng mL⁻¹) in the patient's serum. We fabricated immunoassay chips based on QD photoluminescence (QDs-ELISA) and AuNP Surface Enhanced Raman Scattering (SERS-ELISA) phenomena to detect digoxin in the therapeutic range. Digoxin levels were monitored using digoxin antibodies conjugated to QDs and AuNPs employing the sandwich immunoassay format in both the chips. The limit of detection (LOD) achieved through QDs-ELISA and SERS-ELISA was 0.5 ng mL⁻¹ and 0.4 ng mL⁻¹, respectively. It is demonstrated that the sensitivity of QDs-ELISA was dependent on the charge transfer mechanism from the QDs to the antibody through ionic media, which was further explored using electrochemical impedance spectroscopy. We demonstrate that QDs-ELISA was relatively easy to fabricate compared to SERS-ELISA. The current study envisages replacement of conventional methodologies with small immunoassay chips using QDs and/or SERS-based tags with fast turnaround detection time as compared to conventional ELISA.

Cardiovascular diseases pose a serious health risk and have a high mortality rate of 31% worldwide.

Effects of 1α,25-Dihydroxyvitamin D3 on the Pharmacokinetics of Procainamide and Its Metabolite N-Acetylprocainamide, Organic Cation Transporter Substrates, in Rats with PBPK Modeling Approach

In this study, possible changes in the expression of rat organic cationic transporters (rOCTs) and rat multidrug and toxin extrusion proteins (rMATEs) following treatment with 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) were investigated. Rats received intraperitoneal administrations of 1,25(OH)₂D₃ for four consecutive days, and the tissues of interest were collected. The mRNA expression of rOCT1 in the kidneys was significantly increased in 1,25(OH)₂D₃-treated rats compared with the control rats, while the mRNA expressions of rOCT2 and rMATE1 in the kidneys, rOCT1 and N-acetyltransferase-II (NAT-II) in the liver, and rOCT3 in the heart were significantly decreased. Changes in the protein expression of hepatic rOCT1 and renal rOCT2 and rMATE1 were confirmed by western blot analysis. We further evaluated the pharmacokinetics of procainamide (PA) hydrochloride and its major metabolite N-acetyl procainamide (NAPA) in the presence of 1,25(OH)₂D₃. When PA hydrochloride was administered intravenously at a dose 10 mg/kg to 1,25(OH)₂D₃-treated rats, a significant decrease in renal and/or non-renal clearance of PA and NAPA was observed. A physiological model for the pharmacokinetics of PA and NAPA in rats was useful for linking changes in the transcriptional and translational expressions of rOCTs and rMATE1 transporters to the altered pharmacokinetics of the drugs.

Micro-electrode channel guide (µECG) technology: an online method for continuous electrical recording in a human beating heart-on-chip

Cardiac toxicity still represents a common adverse outcome causing drug attrition and post-marketing withdrawal. The development of relevant in vitro models resembling the human heart recently opened the path towards a more accurate detection of drug-induced human cardiac toxicity early in the drug development process. Organs-on-chip (OoC) have been proposed as promising tools to recapitulate in vitro the key aspects of the in vivo cardiac physiology and to provide a means to directly analyze functional readouts. In this scenario, a new device capable of continuous monitoring of electrophysiological signals from functional in vitro human hearts-on-chip is here presented. The development of cardiac microtissues was achieved through a recently published method to control the mechanical environment, while the introduction of a technology consisting in micro-electrode coaxial guides (µECG) allowed to conduct direct and non-destructive electrophysiology studies. The generated human cardiac microtissues exhibited synchronous spontaneous beating, as demonstrated by multi-point and continuous acquisition of cardiac field potential, and expression of relevant genes encoding for cardiac ion-channels. A proof-of-concept pharmacological validation on 3 drugs proved the proposed model to potentially be a powerful tool to evaluate functional cardiac toxicity.

Interactions of antiepileptic drugs with drugs approved for the treatment of indications other than epilepsy

Introduction: Comorbidities of epilepsy may significantly interfere with its treatment as diseases in the general population are also encountered in epilepsy patients and some of them even more frequently (for instance, depression, anxiety, or heart disease). Obviously, some drugs approved for other than epilepsy indications can modify the anticonvulsant activity of antiepileptics. Areas covered: This review highlights the drug-drug interactions between antiepileptics and aminophylline, some antidepressant, antiarrhythmic (class I-IV), selected antihypertensive drugs and non-barbiturate injectable anesthetics (ketamine, propofol, etomidate, and alphaxalone). The data were reviewed mainly from experimental models of seizures. Whenever possible, clinical data were provided. PUBMED data base was the main search source.Expert opinion: Aminophylline generally reduced the protective activity of antiepileptics, which, to a certain degree, was consistent with scarce clinical data on methylxanthine derivatives and worse seizure control. The only antiarrhythmic with this profile of action was mexiletine when co-administered with VPA. Among antidepressants and non-barbiturate injectable anesthetics, trazodone, mianserin and etomidate or alphaxalone, respectively, negatively affected the anticonvulsant action of some antiepileptic drugs. Clinical data indicate that only amoxapine, bupropion, clomipramine and maprotiline should be used with caution. Possibly, drugs reducing the anticonvulsant potential of antiepileptics should be avoided in epilepsy patients.

Physiologically-Based Pharmacokinetic Modeling for Drug-Drug Interactions of Procainamide and N-Acetylprocainamide with Cimetidine, an Inhibitor of rOCT2 and rMATE1, in Rats

Previous observations demonstrated that cimetidine decreased the clearance of procainamide (PA) and/or N-acetylprocainamide (NAPA; the primary metabolite of PA) resulting in the increased systemic exposure and the decrease of urinary excretion. Despite an abundance of in vitro and in vivo data regarding pharmacokinetic interactions between PA/NAPA and cimetidine, however, a mechanistic approach to elucidate these interactions has not been reported yet. The primary objective of this study was to construct a physiological model that describes pharmacokinetic interactions between PA/NAPA and cimetidine, an inhibitor of rat organic cation transporter 2 (rOCT2) and rat multidrug and toxin extrusion proteins (rMATE1), by performing extensive in vivo and in vitro pharmacokinetic studies for PA and NAPA performed in the absence or presence of cimetidine in rats. When a single intravenous injection of PA HCl (10 mg/kg) was administered to rats, co-administration of cimetidine (100 mg/kg) significantly increased systemic exposure and decreased the systemic (CL) and renal (CL_R) clearance of PA, and reduced its tissue distribution. Similarly, cimetidine significantly decreased the CL_R of NAPA formed by the metabolism of PA and increased the AUC of NAPA. Considering that these drugs could share similar renal secretory pathways (e.g., via rOCT2 and rMATE1), a physiologically-based pharmacokinetic (PBPK) model incorporating semi-mechanistic kidney compartments was devised to predict drug-drug interactions (DDIs). Using our proposed PBPK model, DDIs between PA/NAPA and cimetidine were successfully predicted for the plasma concentrations and urinary excretion profiles of PA and NAPA observed in rats. Moreover, sensitivity analyses of the pharmacokinetics of PA and NAPA showed the inhibitory effects of cimetidine via rMATE1 were probably important for the renal elimination of PA and NAPA in rats. The proposed PBPK model may be useful for understanding the mechanisms of interactions between PA/NAPA and cimetidine in vivo.

Iatrogenic hypertension: a bioinformatic analysis

It is well known that a myriad of medications and substances can induce side effects that are related to blood pressure (BP) regulation. This study aims to investigate why certain drugs tend to cause iatrogenic hypertension (HTN) and focus on drug targets that are implicated in these conditions.Databases and resources such as SIDER, DrugBank, and Genomatix were utilized in order to bioinformatically investigate HTN-associated drug target-genes for which HTN is a side effect. A tree-like map was created, representing interactions between 198 human genes that relate to the blood pressure system. 72 HTN indicated drugs and 160 HTN-inducing drugs were investigated. HTN-associated genes affected by these drugs were identified. HTN indicated drugs, which target nearly all branches of the interaction tree, were shown to exert an effect on most functional sub-systems of the BP regulatory system; and specifically, for the adrenergic and dopaminergic receptor pathways. High prevalence (25 genes) of shared targets between the HTN indicated and HTN-inducing drug categories was demonstrated. We focus on six drug families which are not indicated for HTN treatment, yet are reported as a major cause for blood pressure side effects. We show the molecular mechanisms that may lead to this iatrogenic effect. Such an analysis may have clinical implications that could allow for the development of tailored medicine with fewer side effects.

Simultaneous Determination of Procainamide and N-acetylprocainamide in Rat Plasma by Ultra-High-Pressure Liquid Chromatography Coupled with a Diode Array Detector and Its Application to a Pharmacokinetic Study in Rats

A simple, sensitive, and reliable reversed-phase, Ultra-High-Pressure Liquid Chromatography (UHPLC) coupled with a Diode Array Detector (DAD) method for the simultaneous determination of Procainamide (PA) and its major metabolite, N-acetylprocainamide (NAPA), in rat plasma was developed and validated. A simple deproteinization method with methanol was applied to the rat plasma samples, which were analyzed using UHPLC equipped with DAD at 280 nm, and a Synergi™ 4 µm polar, reversed-phase column using 1% acetic acid (pH 5.5) and methanol (76:24, v/v) as eluent in isocratic mode at a flow rate 0.2 mL/min. The method showed good linearity (r² > 0.998) over the concentration range of 20–100,000 and 20–10,000 ng/mL for PA and NAPA, respectively. Intra- and inter-day accuracies ranged from 97.7 to 110.9%, and precision was <10.5% for PA and 99.7 to 109.2 and <10.5%, respectively, for NAPA. The lower limit of quantification was 20 ng/mL for both compounds. This is the first report of the UHPLC-DAD bioanalytical method for simultaneous measurement of PA and NAPA. The most obvious advantage of this method over previously reported HPLC methods is that it requires small sample and injection volumes, with a straightforward, one-step sample preparation. It overcomes the limitations of previous methods, which use large sample volume and complex sample preparation. The devised method was successfully applied to the quantification of PA and NAPA after an intravenous bolus administration of 10 mg/kg procainamide hydrochloride to rats.

Effect of sotalol on heart rate, QT interval, and atrial fibrillation cycle length in horses with atrial fibrillation

Background

Based on its pharmacokinetic profile and electrophysiological effects in healthy horses, sotalol potentially could be used as a long‐term PO antiarrhythmic drug in horses.

Objectives

To evaluate the effect of sotalol on heart rate (HR), QT interval, atrial fibrillatory rate, and success of cardioversion in horses with naturally occurring chronic atrial fibrillation (AF).

Animals

Twenty‐eight horses referred for transvenous electrical cardioversion of AF were treated with 2 mg/kg sotalol PO q12h for 3 days before cardioversion, and 13 horses underwent the same protocol without sotalol administration.

Methods

Retrospective study. Before and after sotalol or no treatment, the HR was measured at rest and during an exercise test. The QT interval and atrial fibrillation cycle length (AFCL) were measured at rest using tissue Doppler velocity imaging.

Results

In the control group, no significant differences were found between the 2 examinations. In the sotalol group, the HR at rest and during exercise was significantly lower after sotalol treatment, whereas the QT interval and AFCL measured by tissue Doppler increased significantly. Cardioversion to sinus rhythm was achieved in 25/28 horses in the sotalol group and all horses in the control group, but the median number of shocks and energy at cardioversion were significantly lower in the sotalol group.

Conclusions and Clinical Importance

In horses with AF, sotalol administration results in class III antiarrhythmic effects and β‐blocking activity, with moderate HR reduction during exercise.

Influence of propafenone on the anticonvulsant activity of various novel antiepileptic drugs in the mouse maximal electroshock model

BACKGROUND

The main mechanism of action of propafenone (antiarrhythmic drug) involves the inhibition of the fast inward sodium current during phase 0 of the action potential. Sodium channel-blocking activity is also characteristic for some antiepileptic drugs. Therefore, it could be assumed that propafenone may also affect seizures. In the present study, we evaluated the effect of propafenone on the protective effect of oxcarbazepine, lamotrigine, topiramate and pregabalin against the maximal electroshock-induced seizures in mice.

METHODS

Anticonvulsant activity of propafenone was assessed with the maximal electroshock seizure threshold (MEST) test. Influence of propafenone on the anticonvulsant activity of antiepileptic drugs was estimated in the mouse maximal electroshock model (MES). Drug-related adverse effects were determined in the chimney test (motor coordination) and passive-avoidance task (long-term memory). Brain concentrations of antiepileptics were assessed by fluorescence polarization immunoassay.

RESULTS

Propafenone at doses 60-90mg/kg significantly increased the threshold of seizures, in turn at doses 5-50mg/kg did not affect this parameter. Administration of propafenone at the subthreshold dose of 50mg/kg increased antielectroshock activity of oxcarbazepine, topiramate and pregabalin, but not that of lamotrigine. As regards adverse effects, propafenone alone and in combination with antiepileptic drugs did not significantly impair motor coordination or long-term memory in mice. Propafenone (50mg/kg) significantly increased the brain level of pregabalin. Brain concentrations of topiramate and oxcarbazepine were not affected.

CONCLUSION

Our findings show that propafenone has own anticonvulsant action and enhances efficacy of oxcarbazepine, topiramate and pregabalin, but not that of lamotrigine, at least in experimental condition.

Pharmacokinetics and electrophysiological effects of sotalol hydrochloride in horses

BACKGROUND

Arrhythmias in horses may require long-term anti-arrhythmic therapy. Unfortunately, oral anti-arrhythmic drugs for use in horses are currently scarce. In human patients and small animals, sotalol, a β-blocker with class III anti-arrhythmic properties, is often used for long-term treatment.

OBJECTIVES

To determine the pharmacokinetics of sotalol at multiple oral dosages in unfasted horses, as well as the effects on electro- and echocardiographic measurements, right atrial and ventricular monophasic action potential (MAP) and effective refractory period (ERP).

STUDY DESIGN

Placebo controlled, double-blinded experiment.

MATERIALS AND METHODS

Six healthy, unfasted Warmblood horses were given either 0, 2, 3 or 4 mg/kg bodyweight (bwt) sotalol orally (PO) twice daily (bid) for 9 days in a randomised cross-over design. Echocardiography and surface electrocardiography were performed and plasma concentrations of sotalol and right atrial and right ventricular MAPs and ERPs were determined at steady-state conditions. Statistical analysis was performed using a repeated measures univariate analysis with post hoc Bonferroni corrections.

RESULTS

Calculated mean steady-state plasma concentrations determined by nonlinear mixed-effect modelling were 287 (range 234-339), 409 (359-458) and 543 (439-646) ng/mL for 2, 3 and 4 mg/kg bwt sotalol PO bid respectively. Sotalol significantly increased the QT interval and ERPs, but, despite increasing plasma concentrations, higher dosages did not result in a progressive increase in QT interval or ERPs. Echocardiographic and other electrocardiographic measurements did not change significantly. MAP durations at 90% repolarisation were not significantly different during sotalol treatment. Besides transient local sweating, no side effects were noted.

MAIN LIMITATIONS

Study size and ad libitum feeding of hay.

CONCLUSIONS

Sotalol at a dose of 2, 3 and 4 mg/kg bwt PO bid increases the QT interval and ERP and might be a useful drug for long-term anti-arrhythmic therapy in horses.

Drug Dosing in Critically Ill Patients with Renal Failure: A Pharmacokinetic Approach

Accurate pharmacotherapy management in the intensive care unit (ICU) patient is crucial to minimize adverse drug events. Pharmacokinetic principles including absorption, distribution, metabolism, and excretion (ADME) all play an important role in determining the fate of medications used in the critical care setting. Renal failure in this setting further alters pharmacokinetic parameters, resulting in drug dosing changes. This article highlights and applies principles of drug dosing in normal patients and in the pharmacokinetically challenging environment of critically ill patients with renal failure. Specific drug dosing tables serve as a guide for the clinician to renally adjust medication doses in the critically ill patient with renal failure.

Application of a systems pharmacology model for translational prediction of hERG-mediated QTc prolongation

Drug‐induced QTc interval prolongation (ΔQTc) is a main surrogate for proarrhythmic risk assessment. A higher in vivo than in vitro potency for hERG‐mediated QTc prolongation has been suggested. Also, in vivo between‐species and patient populations’ sensitivity to drug‐induced QTc prolongation seems to differ. Here, a systems pharmacology model integrating preclinical in vitro (hERG binding) and in vivo (conscious dog ΔQTc) data of three hERG blockers (dofetilide, sotalol, moxifloxacin) was applied (1) to compare the operational efficacy of the three drugs in vivo and (2) to quantify dog–human differences in sensitivity to drug‐induced QTc prolongation (for dofetilide only). Scaling parameters for translational in vivo extrapolation of drug effects were derived based on the assumption of system‐specific myocardial ion channel densities and transduction of ion channel block: the operational efficacy (transduction of hERG block) in dogs was drug specific (1–19% hERG block corresponded to ≥10 msec ΔQTc). System‐specific maximal achievable ΔQTc was estimated to 28% from baseline in both dog and human, while %hERG block leading to half‐maximal effects was 58% lower in human, suggesting a higher contribution of hERG‐mediated potassium current to cardiac repolarization. These results suggest that differences in sensitivity to drug‐induced QTc prolongation may be well explained by drug‐ and system‐specific differences in operational efficacy (transduction of hERG block), consistent with experimental reports. The proposed scaling approach may thus assist the translational risk assessment of QTc prolongation in different species and patient populations, if mediated by the hERG channel.

Sodium channel-inhibiting drugs and survival of breast, colon and prostate cancer: a population-based study

Metastasis is the leading cause of cancer-related deaths. Voltage-gated sodium channels (VGSCs) regulate invasion and metastasis. Several VGSC-inhibiting drugs reduce metastasis in murine cancer models. We aimed to test the hypothesis that patients taking VGSC-inhibiting drugs who developed cancer live longer than those not taking these drugs. A cohort study was performed on primary care data from the QResearch database, including patients with breast, bowel or prostate cancer. Cox proportional hazards regression was used to compare the survival from cancer diagnosis of patients taking VGSC-inhibiting drugs with those not exposed to these drugs. Median time to death was 9.7 years in the exposed group and 18.4 years in the unexposed group, and exposure to these medications significantly increased mortality. Thus, exposure to VGSC-inhibiting drugs associates with reduced survival in breast, bowel and prostate cancer patients. This finding is not consistent with the preclinical data. Despite the strengths of this study including the large sample size, the study is limited by missing information on potentially important confounders such as cancer stage, co-morbidities and cause of death. Further research, which is able to account for these confounding issues, is needed to investigate the relationship between VGSC-inhibiting drugs and cancer survival.

Detection limit enhancement of antiarrhythmic drugs in human plasma using capillary electrophoresis with dispersive liquid–liquid microextraction and field-amplified sample stacking method

Background: A new capillary zone electrophoresis (CZE) with ultraviolet detection method has been developed and validated for the analysis of four antiarrhythmic drugs in human plasma samples. Methods: In this study, a dispersive liquid–liquid microextraction (DLLME) coupled with field-amplified sample stacking (FASS) was employed for biological samples clean-up and sensitivity enhancement in CZE. Results: Under optimum DLLME-FASS-CZE conditions, enhancement factors were in the range of 157–314. The method was validated over the concentration range of 20–800 ng/ml in human plasma. Inter- and intra-day precision and the accuracy were less than 20%; the detection limits ranged from 2.5 to 4.7 ng/ml. Furthermore, the validated method was successfully applied to the detection of studied drugs in patients’ plasma samples.

Antiarrhythmic drugs and epilepsy

For a long time it has been suspected that epilepsy and cardiac arrhythmia may have common molecular background. Furthermore, seizures can affect function of the central autonomic control centers leading to short- and long-term alterations of cardiac rhythm. Sudden unexpected death in epilepsy (SUDEP) has most likely a cardiac mechanism. Common elements of pathogenesis create a basis for the assumption that antiarrhythmic drugs (AADs) may affect seizure phenomena and interact with antiepileptic drugs (AEDs). Numerous studies have demonstrated anticonvulsant effects of AADs. Among class I AADs (sodium channel blockers), phenytoin is an established antiepileptic drug. Propafenone exerted low anti-electroshock activity in rats. Lidocaine and mexiletine showed the anticonvulsant activity not only in animal models, but also in patients with partial seizures. Among beta-blockers (class II AADs), propranolol was anticonvulsant in models for generalized tonic-clonic and complex partial seizures, but not for myoclonic convulsions. Metoprolol and pindolol antagonized tonic-clonic seizures in DBA/2 mice. Timolol reversed the epileptiform activity of pentylenetetrazol (PTZ) in the brain. Furthermore, amiodarone, the representative of class III AADs, inhibited PTZ- and caffeine-induced convulsions in mice. In the group of class IV AADs, verapamil protected mice against PTZ-induced seizures and inhibited epileptogenesis in amygdala-kindled rats. Verapamil and diltiazem showed moderate anticonvulsant activity in genetically epilepsy prone rats. Additionally, numerous AADs potentiated the anticonvulsant action of AEDs in both experimental and clinical conditions. It should be mentioned, however, that many AADs showed proconvulsant effects in overdose. Moreover, intravenous esmolol and intra-arterial verapamil induced seizures even at therapeutic dose ranges.

The cost effectiveness of implantable cardioverter defibrillators: a systematic review of economic evaluations

BACKGROUND

Sudden cardiac death (SCD) is the most common cause of death in developed countries, with more than 3 million people dying yearly. Implantable cardioverter defibrillators (ICDs) are considered to be an effective treatment in the primary and secondary prevention of SCD; however, their cost is considerable and this poses questions regarding whether they are worth the investment relative to less expensive pharmacotherapy.

OBJECTIVE

The aim of this systematic review is to investigate existing evidence regarding the cost effectiveness of ICD therapy and to identify the key drivers of cost effectiveness, for the purpose of informing interested policy and decision makers.

METHODOLOGY

A systematic review of the literature concerning the cost effectiveness of ICDs was undertaken. Electronic databases, including PubMed, Cochrane and Health Economic Evaluations Database were searched based on appropriate terms and their combinations. Economic evaluation studies that examined the cost effectiveness of ICDs were selected and 34 were included for evaluation.

RESULTS

Findings from the present analysis show that ICD therapy, in properly selected patients who are at high risk of sudden cardiac death, is associated with similar or better cost-effectiveness ratios compared with other well accepted conventional treatments. The cost effectiveness of ICDs is influenced by several factors, including ICD efficacy and safety, impact on patient quality of life, device original implantation cost, frequency and cost of battery replacement, patient demographics and risk profile and analysis time horizon.

CONCLUSION

ICDs may represent a cost-effective option relative to pharmacotherapy in appropriately selected patient groups. The cost-effectiveness ratios appear to be at acceptable and comparable levels to other established treatments in cardiovascular and non-cardiovascular diseases. However, cost effectiveness is highly related to several factors and hence economic efficiency is highly dependent on conditions that need to be fulfilled for each individual case in medical practice. The aforementioned factors and technological advances imply that to ensure cost-effective use of ICD therapy, continuous research is needed.

A highly predictive 3D-QSAR model for binding to the voltage-gated sodium channel: design of potent new ligands

A comprehensive comparative molecular field analysis (CoMFA) model for the binding of ligands to the neuronal voltage-gated sodium channel was generated based on 67 diverse compounds. Earlier published CoMFA models for this target provided μM ligands, but the improved model described here provided structurally novel compounds with low nM IC₅₀. For example, new compounds 94 and 95 had IC₅₀ values of 129 and 119 nM, respectively.

Clinical applications of fast liquid chromatography: a review on the analysis of cardiovascular drugs and their metabolites

One of the major challenges facing the medicine today is developing new therapies that enhance human health. To help address these challenges the utilization of analytical technologies and high-throughput automated platforms has been employed; in order to perform more experiments in a shorter time frame with increased data quality. In the last decade various analytical strategies have been established to enhance separation speed and efficiency in liquid chromatography applications. Liquid chromatography is an increasingly important tool for monitoring drugs and their metabolites. Furthermore, liquid chromatography has played an important role in pharmacokinetics and metabolism studies at these drug development stages since its introduction. This paper provides an overview of current trends in fast chromatography for the analysis of cardiovascular drugs and their metabolites in clinical applications. Current trends in fast liquid chromatographic separations involve monolith technologies, fused-core columns, high-temperature liquid chromatography (HTLC) and ultra-high performance liquid chromatography (UHPLC). The high specificity in combination with high sensitivity makes it an attractive complementary method to traditional methodology used for routine applications. The practical aspects of, recent developments in and the present status of fast chromatography for the analysis of biological fluids for therapeutic drug and metabolite monitoring, pharmacokinetic studies and bioequivalence studies are presented.

An HPLC method for the determination of nifekalant hydrochloride in canine plasma and its application to a pharmacokinetic study

In this study, a simple and selective high-performance liquid chromatography method was developed and validated for the determination of nifekalant hydrochloride in canine plasma. Liquid-liquid extraction was used to separate nifekalant hydrochloride from canine plasma and the mean extraction recoveries of nifekalant hydrochloride and the internal standard were 82.31 and 94.81%, respectively. The chromatographic separation was performed on a Dikma Diamonsil column with a mobile phase consisting of acetonitrile-20mM phosphate buffer (pH 6.2; 30:70, v/v) with flow rate of 1.0 mL/min. The standard curve was linear over the concentration range of 20-10,000 ng/mL (r(2) > 0.99). The intra-batch and inter-batch accuracy for nifekalant hydrochloride at four concentrations were 93.14-100.47% and 96.12-103.77%, respectively. The relative standard deviations were less than 15%. The method was successfully applied to a pharmacokinetic study after the intravenous administration of nifekalant hydrochloride to beagle dogs.

Atrial fibrillation and atrial flutter: medical management

Atrial fibrillation (AF) and atrial flutter (AFL) are common cardiac arrhythmias in older adults. Medical management focuses on rate and rhythm control of AF and AFL to promote symptomatic relief and avoid tachycardia-mediated cardiomyopathy. Pharmacologic treatment of AF and AFL is especially challenging in the elderly because of the presence of comorbidities that may affect drug kinetics, and polypharmacy, which may lead to drug interactions. The potential for complications from medications and procedures required to achieve and maintain sinus rhythm must be carefully balanced against the benefits of therapy. This article reviews medical management of AF and AFL specifically relating to rate and rhythm control. The controversy of rate versus rhythm control is also discussed.

Adherence to Amiodarone Monitoring Recommendations Before and After Implementation of a Centralized Pharmacy Service

The objective of this study was to determine whether patients enrolled in a centralized amiodarone monitoring service (AMS) were more adherent to amiodarone surveillance and whether the incidence of amiodarone-related toxicity differed for patients who were enrolled in the AMS. Amiodarone therapy was initiated in 917 patients in an integrated health care delivery system between October 1998 and December 2006. Electronic records were queried to establish the proportion of patients completing recommended amiodarone monitoring during the first year of therapy; specifically, thyroid stimulating hormone (TSH), alanine aminotransferase (ALT), electrocardiogram (ECG), and chest radiograph (CXR). Patients were assigned to the AMS or control cohort based on when amiodarone was initiated. Patients assigned to the AMS cohort were more likely to receive ALT monitoring at baseline, 6 months, and 1 year (68% vs 44%, P < .001; 86% vs 76%, P = .002; 84% vs 69%, P < .001; respectively) and ECG monitoring at baseline and 1 year (76% vs 58%; 96% vs 75%, P < .001, respectively). There was no difference in TSH monitoring at baseline, 6 months, and 1 year (55% vs 49%, P = not significant [NS]; 74% vs 70%, P = NS; 68% vs 64%, P = NS; respectively).

Post induction arrhythmia in a renal patient: an unexpected risk factor

A 44 year-old woman was anaesthetised for a transplant nephrectomy. About 10 min after induction of anaesthesia she had several runs of ventricular tachycardia followed by ventricular fibrillation requiring 30 s of cardiopulmonary resuscitation, after which she reverted to sinus rhythm. Review of her chest X-ray, suggested that the haemodialysis catheter (Permcath) position may have precipitated this event. However, subsequent investigation found that she had toxic serum levels of sotalol, with a prolonged corrected QT interval on the electrocardiogram. She was started on sotalol while her renal graft was functioning well but it was not reviewed when the graft started to fail and she had to commence haemodialysis. This led to the accumulation of sotalol and explains her serum sotalol value of 7.1 mg x l(-1) on the day of the event. Concentrations greater than 2.5 mg x l(-1) are generally considered toxic.

Evaluation of the inhibitory and induction potential of YM758, a novel If channel inhibitor, for human P450-mediated metabolism

This study was designed to examine the in vitro metabolism of YM758, a novel cardiovascular agent, and to evaluate its potential to cause drug interactions and induction of CYP isozymes. After incubation with pooled human liver microsomes, YM758 was converted to two major metabolites (AS2036313-00, and YM-394111 or YM-394112). The formation of AS2036313-00, and YM-394111 or YM-394112 were mediated by CYP2D6 and CYP3A4, respectively, which was elucidated by using a bank of human liver microsomes and recombinant CYP enzymes in combination with the utilization of typical substrates and inhibitors. The Ki values of YM758 for midazolam, nifedipine, and metoprolol metabolism ranged from 59 to 340 microM, being much higher than the YM758 concentration in human plasma. The formation of AS2036313-00, and YM-394111 or YM-394112 was inhibited by quinidine and ketoconazole with Ki values of 140 and 0.24 microM, respectively, which indicates that YM758 metabolism may be affected by coadministration of strong CYP2D6 and 3A4 inhibitors in vivo, given the clinical plasma concentrations of quinidine and ketoconazole. After human hepatocytes were exposed to 10 microM YM758, microsomal activity and mRNA level for CYP1A2 were not induced while those for CYP3A4 were slightly induced. The tested concentration was much higher than that in human plasma, which suggests that the induction potential of YM758 is also negligible.

Modeling Cardiac Uptake and Negative Inotropic Response of Verapamil in Rat Heart: Effect of Amiodarone

PURPOSE

To determine the effect of the P-glycoprotein (Pgp) modulator amiodarone on the pharmacokinetics and pharmacodynamics (PK/PD) of Pgp substrate verapamil in the perfused rat heart.

METHODS

In Langendorff-perfused rat hearts, the outflow concentration-time curve and inotropic response data were measured after a 1.5 nmol dose of [3H]-verapamil (infused within 1 min) in the absence and presence of the amiodarone (1 microM) in perfusate, as well as using a double dosing regimen (0.75 nmol in a 10 min interval). These data were analyzed by a PK/PD model.

RESULTS

Amiodarone failed to influence the rapid uptake and equilibrium partitioning of verapamil into the heart. The time course of the negative inotropic effect of verapamil, including the 'rebound' above the original baseline after the infusion of verapamil was stopped, could be described by a PK/PD tolerance model. Tolerance development (mean delay time, 12 min) led to a reduction in predicted steady-state effect (16%). The EC50 and Emax values as estimated in single dose experiments were 16.4+/-4.1 nM and 50.5+/-18.9 mmHg, respectively.

CONCLUSIONS

The result does not support the hypothesis that Pgp inhibition by amiodarone increases cardiac uptake of the Pgp substrate verapamil.

Development of an optimal lidocaine infusion strategy for neonatal seizures

INTRODUCTION

Lidocaine is an effective drug for the treatment of neonatal convulsions not responding to traditional anticonvulsant therapy. However, one of the side-effects is a risk of cardiac arrhythmias. The aim of this study was to develop an optimal dosing strategy with minimal risk of cardiac arrhythmias.

MATERIALS AND METHODS

As a first step, we studied 20 neonates during routine treatment of neonatal seizures with lidocaine. All were given a loading dose of 2 mg/kg in 10 min, followed by the continuous infusion of 6 mg/kg per hour for 12 h, 4 mg/kg per hour for 12 h and finally 2 mg/kg per hour for 12 h. Effectiveness, cardiac toxicity and lidocaine plasma concentrations were then determined.

RESULTS

No cardiac arrhythmias were observed, and lidocaine was effective in 76% of the treatments. In most of the treatments (13 out of 20) maximal lidocaine plasma concentrations were >9 mg/L. Plasma levels >9 mg/L have been related to cardiac toxicity when used as an anti-arrhythmic drug in adults. It was of interest that all preterm infants showed high lidocaine plasma levels. Secondly, we developed the optimal dosing regimen, which was defined as an infusion regimen at which maximal lidocaine plasma concentrations are <9 mg/L. Simulations with the developed pharmacokinetic model indicated a reduction in the infusion duration of lidocaine at 6 mg/kg per hour from 12 to 6 h. Thirdly, the new lidocaine dosing regimen was evaluated. Fifteen neonates (16 treatments) were studied. No cardiac arrhythmias were observed, and lidocaine was effective in 78% of the treatments. In most of the treatments (11 out of 16) maximal lidocaine plasma concentrations were <9 mg/L. Again preterm infants showed relatively high lidocaine plasma levels.

CONCLUSION

A new lidocaine dosing schedule was developed. This new regimen should have a lower risk of cardiac arrhythmias and appears to be as effective in term infants. For preterm infants the optimal regimen needs to be determined.

Appropriate dosing of antiarrhythmic drugs in Japan requires therapeutic drug monitoring*

OBJECTIVE

In general, drugs are used in accordance with an approved dosage regimen in expectation of an appropriate balance between efficacy and toxicity. However, dose control of drugs with a narrow therapeutic range and marked intersubject variability in pharmacokinetics should be established through individualization of dosing based on therapeutic drug monitoring (TDM). The purpose of this study was to examine differences between the approved dosage regimen and the doses of antiarrhythmic drugs and digoxin used in clinical practice and to examine the influence of TDM on dosing.

METHODS

Prescription research of antiarrhythmic drugs was performed at five national hospitals in Japan. Prescriptions for antiarrhythmic drugs (cibenzoline, disopyramide, pirmenol, mexiletine, aprindine, flecainide, pilsicainide, amiodarone and digoxin) were counted for the study period. The mean dose and dose distribution of the drugs were determined in each hospital. Comparisons were made of mean dose obtained in the study with the dosage approved by the authority. In addition, the percentage of patients that received TDM was determined.

RESULTS

A difference was seen between the approved dosage and the actual dose. For all drugs except flecainide, the mean dose was smaller than the approved dosage. For all drugs except digoxin, remarkable variations were seen in the dose distribution among the hospitals. Digoxin showed a similar dose distribution among the five hospitals. Overall, the percentage of patients that received TDM was low except for Hospital A. However, TDM of digoxin was relatively common at four of the hospitals.

CONCLUSIONS

It is concluded that, with the exception of digoxin, the appropriate dosing regimen for antiarrhythmic drugs is not yet established. The establishment of appropriate dosing regimens for antiarrhythmic drugs requires the more widespread adoption of TDM.

Therapeutic drug monitoring of antiarrhythmic drugs

Most antiarrhythmic drugs fulfil the formal requirements for rational use of therapeutic drug monitoring, as they show highly variable plasma concentration profiles at a given dose and a direct concentration-effect relationship. Therapeutic ranges for antiarrhythmic drugs are, however, often very poorly defined. Effective drug concentrations are based on small studies or studies not designed to establish a therapeutic range, with varying dosage regimens and unstandardised sampling procedures. There are large numbers of nonresponders and considerable overlap between therapeutic and toxic concentrations. Furthermore, no study has ever shown that therapeutic drug monitoring makes a significant difference in clinical outcome. Therapeutic concentration ranges for antiarrhythmic drugs as they exist today can give an overall impression about the drug concentrations required in the majority of patients. They may also be helpful for dosage adjustment in patients with renal or hepatic failure or in patients with possible toxicological or compliance problems. Their use in optimising individual antiarrhythmic therapy, however, is very limited.

Ventricular preexcitation sensitive to flecainide in late stage chick embryo ECGs: 2,3,7,8-tetrachlorodibenzo-p-dioxin impairs inotropic but not chronotropic or dromotropic responses to isoproterenol and confers resistance to flecainide

ECGs free of movement artefacts were obtained without anesthesia in 16- to 18-day-old chick embryos close to hatching and used to study the effect of the environmental toxin 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) on cardiac rhythm and conduction. The ECGs of normal late stage chick embryos exhibited short PR intervals, frequent nonisoelectric PR segments, delta waves, and inverted T waves. Those ECG characteristics are found in patients with the Wolff-Parkinson-White syndrome (WPW) in which they reflect ventricular preexcitation associated with the use of accessory conduction pathways and arrhythmias. Isoproterenol (30 microg/egg) did not alter the ECG preexcitation characteristics. Flecainide, a sodium channel blocker used clinically to suppress WPW accessory pathway activity, at 0.5 to 5 mg per egg diminished the preexcitation and caused atrioventricular (AV) block, supporting the use of accessory pathways together with AV-nodal conduction in normal late stage chick embryos. The findings challenge the dogma that accessory pathways are entirely replaced by AV conduction pathways in late fetal development. TCDD, at 1-2 nmol per egg for 48 h, did not affect heart rate, the increase in heart rate by isoproterenol, or the ECG characteristics, suggesting that short-term TCDD treatment did not affect sinus node function or cardiac conduction. The latter results taken together with prior findings indicate that TCDD differentially impairs the inotropic and lusitropic effects but not the chronotropic or dromotropic effects of isoproterenol. In TCDD-treated embryos, flecainide, tested at 5 mg per egg, caused much less inhibition of preexcitation or production of AV block than in the untreated or solvent-treated controls. The resistance to flecainide represents a new TCDD effect consistent with the reported increase of cardiac myocyte [Ca(2+)](i) by TCDD treatment.

Disposition of propafenone in a poor metabolizer of CYP2D6 with Gilbert's syndrome

Gilbert's syndrome, a genetic deficiency in bilirubin UDP-glucuronosyltransferase (UGT1A1), may dispose to increased toxicity of propafenone in poor metabolizers (PMs) of cytochrome P4502D6 because glucuronidation of propafenone is the major metabolic pathway for drug elimination in PMs. A patient with Gilbert's syndrome who is also PM participated in an interaction study with propafenone and rifampicin along with five otherwise healthy PMs. Using stable isotope techniques, the pharmacokinetics of single doses of 140 mg propafenone i.v. (unlabelled) and 300 mg propafenone p.o. (labelled) were compared between the index patient and the five healthy controls. Propafenone did not accumulate in the plasma of the index patient either before or during induction: AUC(0-infinity) of propafenone in the index patient was within the 95% confidence interval of controls; AUC(0-infinity) of propafenone glucuronide and amount of urinary excretion of propafenone glucuronide in the patient were within or even greater than the 95% confidence intervals of controls. Therefore, individuals with Gilbert's syndrome who also have a PM phenotype appear to be at no higher risk for toxicity of propafenone than otherwise healthy PMs. An indirect conclusion from these in vivo data might be that propafenone is not a substrate of the UGT1A1 isoform.

Suppressive actions of betaxolol on ionic currents in retinal ganglion cells may explain its neuroprotective effects

Betaxolol, a beta 1-selective adrenoceptor antagonist, is widely used in the treatment of glaucoma. In addition to its ocular hypotensive effects, betaxolol has been suggested to act as a retinal neuroprotective agent (Osborne et al., 1997). To investigate possible mechanisms underlying the neuroprotective effects, we tested the actions of betaxolol on ion channels and calcium signaling in isolated retinal ganglion cells. Betaxolol (50 microM) reduced by about 20% the high-voltage-activated (HVA) Ca channel currents in ganglion cells isolated from tiger salamander retina. In contrast, the beta 1-adrenoceptor antagonists propranolol (10 microM) and timolol (50 microM) had no inhibitory actions on HVA Ca channel currents. The L-type Ca channel antagonist, nisoldipine, blocked the HVA Ca channel current partially and the remaining current was not inhibited by betaxolol. Outward current was inhibited in the presence of betaxolol. Both iberiotoxin (IBTX; 10 nM), a selective inhibitor of large-conductance Ca-activated K channels, and Cd2+ (100 microM), which suppresses Ca-activated K channels subsequent to its block of Ca channels, reduced outward current and the remaining current was not blocked significantly with betaxolol. In the presence of betaxolol, Na channel currents were reduced by about 20%, as were currents evoked by glutamate (10 mM) and GABA (1 mM). Current clamp recordings from isolated ganglion cells showed that betaxolol had several effects on excitability: spike height decreased, repetitive spike activity was suppressed, spike width increased and hyperpolarization following spikes was reduced. Calcium imaging in isolated rat retinal ganglion cells revealed that betaxolol inhibited glutamate-induced increases in [Ca2+]i. These results suggest that betaxolol has a diversity of suppressive actions on ganglion cell ion channels and that, as a consequence, one of the net actions of the drug is to reduce Ca2+ influx. The subsequent reduction in [Ca2+]i may contribute to the apparent neuroprotective actions of betaxolol in promoting ganglion cell survival following ischemic insult, as may occur in glaucoma and retinal disease.

Review of common adverse effects of selected antiarrhythmic drugs

The management of cardiac arrhythmias has changed dramatically over the past several years. New drugs and devices are now available to treat various arrhythmias. Many new agents have been developed that rely on different electrophysiologic mechanisms to elicit their effect on the heart rhythm. Though often effective, these drugs also pose a risk because all of them have a variety of potential adverse effects associated with their use. Many of these adverse reactions are common to all antiarrhythmic drugs, whereas others are unique to particular agents. This review discusses the notable adverse effects of selected antiarrhythmic drugs.

Target concentration intervention: beyond Y2K

Target concentration intervention (TCI) is proposed as an alternative conceptual strategy to therapeutic drug monitoring (TDM). It is argued that the idea of a therapeutic range has limited the interpretation of measured drug concentrations and diminished the anticipated clinical benefit to patients by use of an oversimplified pharmacodynamic model. TCI on the other hand embraces pharmacokinetic and pharmacodynamic concepts and uses the idea of a target effect and associated target concentration to make rational individual dose decisions.