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

Development, validation and long-term evaluation of a liquid chromatography-tandem mass spectrometry method for simultaneous quantification of amiodarone, desethylamiodarone and mexiletine in human plasma and serum

Amiodarone and mexiletine are used for ventricular arrhythmias, for which a combination therapy of both anti-arrhythmic drugs (AADs) is not uncommon. Therapeutic drug monitoring (TDM) can be beneficial for clinical guidance of therapy, especially to correctly identify adverse events. Desethylamiodarone, the active metabolite of amiodarone, accumulates over time and is associated with serious adverse events. Therefore, simultaneous TDM for amiodarone, desethylamiodarone and mexiletine is advantageous in clinical practice. The presented LC-MS/MS method was validated for selectivity, matrix effect, linearity, accuracy, precision, carry-over and stability. The method was continuously evaluated during eight months of clinical use. The method was shown to be linear within the measured range of 0.1 to 10 mg/L for each component. The matrix effect was considered negligible. No interfering responses were found for amiodarone, desethylamiodarone and the isotopic-labeled internal standards. A constant and reproducible within-run contribution of 45.3 %, originating from the system, was identified for mexiletine. The systemic contribution to the peak area of the lowest quantifiable concentration of mexiletine affected the selectivity and carry-over effect measurements. Multiple measurements showed that regression adjusted concentrations were accurate and reproducible, indicating calibration correction was applicable. Sample stability was found to be within limits for all storage conditions and freeze-thaw cycles. Furthermore, long-term method evaluation with external controls resulted in stable measurements with a percentage coefficient of variance between 1.3 % and 6.3 %. The presented practical and reliable method is applicable for clinical TDM and will allow clinical practitioners to guide drug therapy of amiodarone and mexiletine.

Modulation of cardiac ventricular conduction: Impact on QRS duration, amplitude and dispersion

Alterations in cardiac impulse conduction may exert both beneficial and detrimental effects. The assessment of ventricular conduction properties is of paramount importance both in clinical and in experimental settings. Currently the duration of the QRS complex is regarded as hallmark of in-vivo assessment of global ventricular conduction time. In addition, the amplitude of the QRS complex has been suggested to reflect ventricular conduction time in man and in rats. Here, for the first time, we systematically investigated the relationship between QRS duration ("QRS") and QRS amplitude ("RS-height"; RSh) in the murine ECG obtained during anesthesia. In mice harbouring a homozygous knockout of the transmembrane protein podoplanin (PDPN-/-; n = 10) we found both a shorter QRS and a greater RSh than in wild-type animals (n = 13). In both genotypes cumulative i.p. administration of 5 mg/kg and 10 mg/kg of the Na channel blocker flecainide resulted in dose-dependent QRS increase and RSh decrease, whereby the drug-induced changes in RSh were greater than in QRS. In both genotypes the flecainide-induced changes in QRS and in RSh were significantly correlated with each other (R = -0.56, P = 0.004). Whereas dispersion of QRS and RSh was similar between genotypes, dispersion of the ratio QRS/RSh was significantly smaller in PDPN-/- than in wild-types. We conclude that in the murine ECG QRS is inversely related to RSh. We suggest that both parameters should be considered in the analysis of ventricular conduction time in the murine ECG.

Direct analysis in real time-mass spectrometry for rapid quantification of five anti-arrhythmic drugs in human serum: application to therapeutic drug monitoring

Therapeutic drug monitoring (TDM) is necessary for the optimal administration of anti-arrhythmic drugs in the treatment of heart arrhythmia. The present study aimed to develop and validate a direct analysis in real time tandem mass spectrometry (DART–MS/MS) method for the rapid and simultaneous determination of five anti-arrhythmic drugs (metoprolol, diltiazem, amiodarone, propafenone, and verapamil) and one metabolite (5-hydroxy(OH)-propafenone) in human serum. After the addition of isotope-labeled internal standards and protein precipitation with acetonitrile, anti-arrhythmic drugs were ionized by DART in positive mode followed by multiple reaction monitoring (MRM) detection. The use of DART–MS/MS avoided the need for chromatographic separation and allowed rapid and ultrahigh throughput analysis of anti-arrhythmic drugs in a total run time of 30 s per sample. The DART–MS/MS method yielded satisfactory linearity (R² ≥ 0.9906), accuracy (86.1–109.9%), and precision (≤ 14.3%) with minimal effect of biological matrixes. The method was successfully applied to analyzing 30 clinical TDM samples. The relative error (RE) of the concentrations obtained by DART–MS/MS and liquid chromatography-tandem mass spectrometry (LC–MS/MS) was within ± 13%. This work highlights the potential usefulness of DART for the rapid quantitative analysis of anti-arrhythmic drugs in human serum and gives rapid feedback in the clinical TDM practices.

Frequency of Clinical Monitoring of Serum Concentrations of Digoxin, Potassium, and Creatinine, and Recording of Electrocardiograms in Digoxin-Treated Patients: A Japanese Claims Database Analysis

Guidelines for cardiovascular drug therapy recommend monitoring serum digoxin concentration (SDC) in patients receiving digoxin treatment, especially those with renal dysfunction and hypokalemia. However, only a few studies have reported the prevalence of SDC monitoring and laboratory testing in clinical practice. Therefore, the aim of this study was to describe the frequency of SDC monitoring and laboratory testing in digoxin users and to assess the association between SDC monitoring and patient characteristics. We used the Japanese insurance claims data covering approximately 1.7 million patients aged 20-74 years between January 1, 2005 and March 31, 2014. All patients who had at least one prescription for digoxin were included. The frequency of SDC and laboratory tests was calculated and the association between patient characteristics and SDC monitoring was assessed using logistic regression analysis. A total of 98867 prescriptions of digoxin were issued to 3458 patients between 2005 and 2014. The annual mean frequencies of monitoring SDC, serum potassium level and serum creatinine level and of recording electrocardiograms was 16.8, 34.8, 38.7, and 24.1%, respectively. Atrial fibrillation, chronic heart failure, renal diseases, and use of oral anticoagulants were associated with SDC monitoring. We found the frequency of SDC monitoring to be relatively low in Japanese clinical practice.

Efficacy of Antiarrhythmic Drugs Short-Term Use After Catheter Ablation for Atrial Fibrillation (EAST-AF) trial

AIMS

Substantial portion of early arrhythmia recurrence after catheter ablation for atrial fibrillation (AF) is considered to be due to irritability in left atrium (LA) from the ablation procedure. We sought to evaluate whether 90-day use of antiarrhythmic drug (AAD) following AF ablation could reduce the incidence of early arrhythmia recurrence and thereby promote reverse remodelling of LA, leading to improved long-term clinical outcomes.

METHODS AND RESULTS

A total of 2038 patients who had undergone radiofrequency catheter ablation for paroxysmal, persistent, or long-lasting AF were randomly assigned to either 90-day use of Vaughan Williams class I or III AAD (1016 patients) or control (1022 patients) group. The primary endpoint was recurrent atrial tachyarrhythmias lasting for >30 s or those requiring repeat ablation, hospital admission, or usage of class I or III AAD at 1 year, following the treatment period of 90 days post ablation. Patients assigned to AAD were associated with significantly higher event-free rate from recurrent atrial tachyarrhythmias when compared with the control group during the treatment period of 90 days [59.0 and 52.1%, respectively; adjusted hazard ratio (HR) 0.84; 95% confidence interval (CI) 0.73-0.96; P = 0.01]. However, there was no significant difference in the 1-year event-free rates from the primary endpoint between the groups (69.5 and 67.8%, respectively; adjusted HR 0.93; 95% CI 0.79-1.09; P = 0.38).

CONCLUSION

Short-term use of AAD for 90 days following AF ablation reduced the incidence of recurrent atrial tachyarrhythmias during the treatment period, but it did not lead to improved clinical outcomes at the later phase.

CYP2D6 genotype affects age-related decline in flecainide clearance: a population pharmacokinetic analysis

OBJECTIVE

To investigate the association between age-related decline in flecainide clearance and CYP2D6 genotype, we conducted a population pharmacokinetic analysis of flecainide using routine therapeutic drug monitoring data.

METHODS

Population pharmacokinetic analysis was performed on retrospective data from 163 genotyped patients treated with oral flecainide for supraventricular tachyarrhythmias. The CYP2D6 genotype was categorized as CYP2D6 homozygous extensive metabolizers (hom-EMs; n=57), heterozygous extensive metabolizers (het-EMs; n=79), and intermediate metabolizers and poor metabolizers (IMs/PMs; n=27).

RESULTS

Population pharmacokinetic analysis revealed that estimated glomerular filtration rate, body weight, female sex, and aging were important factors for estimating flecainide clearance. The metabolic clearance was decreased age dependently in a curvilinear fashion, where the lower clearance was observed in greater than 60 years for het-EMs and greater than 55 years for IMs/PMs. The reduction in metabolic clearance in elderly (70 years) patients compared with middle-aged (52 years) patients was different among the CYP2D6 genotype groups: 22.1 and 49.5% in CYP2D6 het-EMs and IMs/PMs, respectively, and no change in hom-EMs. A 11.4% reduction in estimated glomerular filtration rate in elderly patients compared with middle-aged patients corresponded to 6.1% decline in flecainide clearance. Overall, the age-related decline in flecainide clearance was 6.1% in hom-EMs, 16.3% in het-EMs, and 28.9% in IMs/PMs groups.

CONCLUSION

This study suggests that CYP2D6 genotype is a determinant factor of age-related decline in flecainide clearance.

Exploring differences in drug doses between Japan and Western countries

Japan is unique among Asian countries in that it requires inclusion of substantial domestic clinical trial data in new drug application data packages. Some question the need for this and call for globalization of approved doses. The current study examines international differences in maximum daily dose of drugs approved in Japan between 2001 and 2007, and for all cardiovascular system (CVS) and central nervous system (CNS) drugs marketed in Japan. For 32% of the drugs approved in Japan between 2001 and 2007, the maximum recommended dose in the United States was > or =2 times higher than the maximum dose approved in Japan. Dose differences were rare for antitumor and antiviral drugs and also for priority-review and orphan drugs. Of all the price-listed CVS drugs currently available in Japan, 65% had maximum doses that were > or =2 times higher in the Netherlands than in Japan; similarly, 57% of the drugs had maximum doses that were > or =2 times higher in the United States than in Japan. For CNS drugs, these figures were 32% (the Netherlands) and 29% (United States). These results underscore the necessity to carry out quantitative analyses to determine the causes of these differences.

Gender-associated differences in pharmacokinetics and anti-arrhythmic effects of flecainide in Japanese patients with supraventricular tachyarrhythmia

OBJECTIVE

We examined the effect of gender-associated differences in pharmacokinetics on the anti-arrhythmic effects of flecainide in Japanese patients with supraventricular tachyarrhythmia and in healthy subjects.

METHODS

The study population comprised 72 outpatients (52 males and 20 females) treated with oral flecainide for supraventricular tachyarrhythmias. Serum flecainide concentrations were determined by use of high-performance liquid chromatography. The anti-arrhythmic efficacy of flecainide was assessed for at least 2 months through evaluation of symptomatology, electrocardiograms, and Holter monitoring. Pharmacokinetics of flecainide after a single 50-mg dose was examined in 14 healthy subjects (7 males and 7 females).

RESULTS

The daily dose of flecainide did not differ between males and females (2.87 +/- 0.68 versus 2.92 +/- 0.90 mg/kg). The serum flecainide concentration was significantly lower in males than in females (315 +/- 151 versus 408 +/- 184 ng/mL, P < 0.05). Clinically relevant efficacy of flecainide was achieved significantly (P < 0.05) less often in male patients (31 of 52; 60%) than in female patients (19 of 20; 95%). We confirmed that nonrenal clearance of flecainide among healthy subjects was significantly higher in males than in females (0.77 +/- 0.16 versus 0.57 +/- 0.06 L h(-1) kg(-1), P < 0.05).

CONCLUSIONS

Our results suggest that the anti-arrhythmic efficacy of flecainide differed between males and females because of gender-associated differences in pharmacokinetics.

Simultaneous determination of ten antiarrhythic drugs and a metabolite in human plasma by liquid chromatography—tandem mass spectrometry

A simple, accurate and selective LC-MS/MS method was developed and validated for simultaneous quantification of ten antiarrhythic drugs (diltiazem, amiodarone, mexiletine, propranolol, sotalol, verapamil, bisoprolol, metoprolol, atenolol, carvedilol) and a metabolite (norverapamil) in human plasma. Plasma samples were simply pretreated with acetonitrile for deproteinization. Chromatographic separation was performed on a Capcell C(18) column (50mmx2.0mm, 5microm) using a gradient mixture of acetonitrile and water (both containing 0.02% formic acid) as a mobile phase at flow rate of 0.3ml/min. The analytes were protonated in the positive electrospray ionization (ESI) interface and detected in multiple reaction monitoring (MRM) mode. Calibration curves were linear over wide ranges from sub- to over-therapeutic concentration in plasma for all analytes. Intra- and inter-batch precision of analysis was <12.0%, accuracy ranged from 90% to 110%, average recovery from 85.0% to 99.7%. The validated method was successfully applied to therapeutic drug monitoring (TDM) of antiarrhythic drugs in routine clinical practice.

Effect of CYP2D6 genotype on flecainide pharmacokinetics in Japanese patients with supraventricular tachyarrhythmia

OBJECTIVE

To examine the effect of CYP2D6 genotype on the pharmacokinetics of flecainide, we conducted a population pharmacokinetic analysis of the data collected during routine therapeutic drug monitoring of Japanese patients with supraventricular tachyarrhythmia.

METHODS

Population analysis was performed on retrospective data from 58 patients with normal kidney and liver function treated with oral flecainide for supraventricular tachyarrhythmia. Serum concentrations of flecainide were determined by high-performance liquid chromatography. CYP2D6 genotyping for extensive metabolizer (EM), intermediate metabolizer (IM) and poor metabolizer (PM) alleles was conducted by allele-specific polymerase chain reaction (PCR) and stepdown PCR. WinNonMix was used to estimate oral clearance (CL/F) of flecainide with a one-compartment model for first-order absorption.

RESULTS

Body weight, age, sex, serum creatinine concentration (Scr), and CYP2D6 genotype influenced flecainide pharmacokinetics. The CL/F was affected by age (30% reduction in > or =70 years old) and sex (24% reduction in females). The ratios of CL/F for the five CYP2D6 genotypes were: 1.00 (EM/EM), 0.89 (EM/IM), 0.84 (EM/PM), 0.79 (IM/IM), 0.73 (IM/PM). A model including these five covariates reduced the interpatient variability of CL/F from 32.9% (base model) to 17.8%. Using a Bayesian method we estimated that the CL/F in IMs was significantly lower than in homozygous EMs (0.25+/-0.05 l h(-1) kg(-1) vs. 0.37+/-0.08 l h(-1) kg(-1), P<0.05) among male patients under 70 years old.

CONCLUSIONS

CYP2D6 genotype, even in IMs, as well as body weight, age, sex, and Scr influence flecainide pharmacokinetics in Japanese patients with supraventricular tachyarrhythmia.

Heart Failure Elevates Serum Levels of Cibenzoline in Arrhythmic Patients

BACKGROUND

Cibenzoline dosing is generally based on renal function, but serum concentrations might be greater than the expected therapeutic levels when standard oral dosing is used. Because heart failure might modify cibenzoline pharmacokinetics, the difference in cibenzoline pharmacokinetics between patients with and without heart failure was evaluated.

METHODS AND RESULTS

The study enrolled 368 patients (233 men, 135 women) that had been hospitalized and received cibenzoline therapy at the National Cardiovascular Center from January 2001 to May 2005. There were 89 patients with heart failure (51 men, 38 women) and 279 patients without heart failure (182 men, 97 women). They had therapeutic drug monitoring > or = 3 days after the beginning of treatment with cibenzoline. Brain natriuretic peptide (BNP) was measured in 81 patients (50 men, 31 women) concurrently with therapeutic drug monitoring of cibenzoline. The difference in serum cibenzoline concentration/(dose/weight) (C/D) values between patients with and without heart failure was analyzed using analysis of covariance (ANCOVA) with creatinine clearance (Ccr) serving as the covariate. The effects of dose/weight and the log-transformed BNP (log-BNP) values on serum cibenzoline concentrations were also assessed using ANCOVA. There were 135 and 361 measurements of serum cibenzoline concentration in patients with and without heart failure, respectively. Pearson's correlation coefficient analyses in the patients with and without heart failure revealed that the C/D values were significantly correlated with Ccr (with heart failure, y = -0.837x + 169, r = -0.211, p = 0.014; without heart failure, y = -0.789x + 132, r = -0.393, p < 0.001), and the ANCOVA model indicated that C/D values were significantly higher in patients with heart failure than without heart failure. The ANCOVA model also showed that dose/weight, Ccr and the log-BNP value were significant factors.

CONCLUSIONS

The selection of a cibenzoline dose based only on renal function may increase the risk of toxicity in patients with heart failure. Cardiac function should be taken into account in cibenzoline dosing. The log-BNP may be a useful index for predicting serum cibenzoline concentrations.