Quantitation of Flecainide, Mexiletine, Propafenone, and Amiodarone in Serum or Plasma Using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Flecainide, mexiletine, propafenone, and amiodarone are antiarrhythmic drugs that are used primarily in the treatment of cardiac arrhythmias. The monitoring of the use of these drugs has applications in therapeutic drug monitoring and overdose situations. LC-MS/MS is used to analyze plasma/serum extracts with loxapine as the internal standard to ensure accurate quantitation and control for any potential matrix effects. Positive ion electrospray is used to introduce the analytes into the mass spectrometer. Selected reaction monitoring of two product ions for each analyte allows for the calculation of ion ratios which ensures correct identification of each analyte, while a matrix matched calibration curve is used for quantitation.

Lesson of the month 1: Acute flecainide overdose and the potential utility of lipid emulsion therapy

Lipid-emulsion therapy (Intralipid®) has been advocated as a potential treatment for the management of cardio-toxicity arising from lipid-soluble drugs, particularly those acting upon sodium channels. This, on the basis of a number of ex vivo studies and animal models, suggests that partitioning a drug into lipid could alter its pharmacokinetics and result in significant clinical improvements. Its subsequent use in clinical case series has been seen as confirmation of this mechanism of action. While there are undoubtedly instances where lipid emulsion therapy has been associated with a desirable outcome in humans, as described in this case report, clinicians are reminded that they should not attribute causality, on this basis alone.

[Flecainide poisoning]

Flecainide is an antiarrhythmic drug that blocks sodium channels during phase 0 of cardiac action potential, delaying conduction and reducing contractility. Intoxication by this drug is rare. Onset of effect, which is rapid, takes the form of hypotension and cardiac arrhythmias; mortality is high. No antidote is available and management is based on the few cases that have been reported. The metabolism of flecainide is affected by both kidney and liver failure, which lead to accumulation of the drug. Flecainide should not be used in patients with such failure unless the potential benefits clearly outweigh the risks. If flecainide is prescribed, diligent clinical, electrocardiographic, and hemodynamic vigilance is imperative and plasma levels of the drug should be monitored. We report a case of flecainide poisoning in which the drug was prescribed to treat atrial fibrillation in a woman with resolving sepsis with renal and hepatic complications.

Assessment of serum flecainide trough levels in patients with tachyarrhythmia

The reported therapeutic range for trough flecainide concentration is 200–1000 ng mL−1. Severe adverse events, such as ventricular arrhythmias, have occurred occasionally in patients whose serum flecainide exceeded 1000 ng mL−1. However, the lower limit remains controversial. We have evaluated blood flecainide concentrations in patients with tachyarrhythmia who received the drug to control palpitation. We measured the flecainide trough levels and incidence and frequency of palpitation of 44 outpatients receiving oral flecainide (150–300 mg daily). Mean serum flecainide trough concentrations differed significantly between patients with (n = 14) and without (n = 30) palpitation (259.5 ± 85.2 vs 462.2 ± 197.7 ng mL−1, P < 0.01). The frequency of palpitation decreased as the serum flecainide concentration increased. The incidence of palpitation was 65% at serum flecainide concentrations < 300 ng mL−1 and 11% at ≥ 300 ng mL−1. QRS values were increased significantly in patients with serum flecainide ≥ 300 ng mL−1 compared with < 300 ng mL−1 (0.110 ± 0.016s vs 0.093 ± 0.019s, P < 0.05). We concluded that to control paroxysm in patients receiving flecainide for tachyarrhythmia serum flecainide concentrations should be maintained at ≥ 300 ng mL−1.

Long-term efficacy of flecainide in paroxysmal atrial fibrillation

The efficacy and safety of flecainide for long-term prevention of paroxysmal atrial fibrillation (AF) were studied in an open trial. Twenty patients with very frequent attacks (mean 13 per month) of paroxysmal AF for many years (mean 8 years) participated. Before inclusion, the patients had unsuccessfully been treated with an average of 3.3 antiarrhythmic drugs. Efficacy was jugded from a carefully kept diary in which the patients made daily notes of any AF attacks and possible side-effects from 1 month before treatment until the end of a follow-up period of 6 months. Twelve patients (60%) were completely free from AF and 11 of these are still successfully treated with flecainide after 11-38 months (mean 24 months). Flecainide plasma levels did not differ between responders and non-responders. Eleven patients (55%) had adverse effects but these were usually mild and well tolerated, necessitating withdrawal or dose reduction resulting in relapse of AF only in three patients (15%). No proarrhythmic events were seen.

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.

Haemolysis alters plasma flecainide levels in newborn infants

Refractory neonatal supra-ventricular tachycardia may require the use of flecainide as anti-arrhythmic. Close control of plasma levels is mandatory due to pro-arrhythmic complications. However, inadvertent hemolysis during blood sampling may cause an increase in measured plasma flecainide concentrations. We conclude, therefore, that dosing of the drug should be always done with caution, and in case of suspected haemolysis plasma levels should be repeated with a new blood sample.

Differentiation of the electrophysiological effects on the atrial myocardium between the pure Na channel blocker, pilsicainide, and flecainide

The purpose of this study was to identify the difference between the pure Na channel blocker, pilsicainide and Ic-antiarrhythmic drug, flecainide, on the atrial electrophysiological characteristics.

METHODS

The subjects consisted of 24 patients (48 +/- 12 years-old: P-group) in whom pilsicainide was administrated intravenously (1 mg/kg/10 min) and 31 patients (47 +/- 15 years-old: F-group) in whom flecainide was administrated intravenously (2 mg/kg/10 min). The atrial effective refractory period (ERP-A), intra-atrial conduction time (CT), max intra-atrial conduction delay (Max CD), repetitive atrial firing zone (RAFZ), fragmented atrial activity zone (FAZ) and intra-atrial conduction delay zone (CDZ) were measured before and after the drugs.

RESULTS

Pilsicainide and flecainide significantly prolonged the ERP-A (211 +/- 27 msec to 246 +/- 39 msec; p < 0.001, 217 +/- 25 msec to 244 +/- 33 msec; p < 0.001, respectively) and CT (121 +/- 33 msec to 149 +/- 43 msec; p < 0.001, 122 +/- 22 msec to 153 +/- 27 msec; p < 0.001, respectively) to the same degree. However, the Max CD was shortened by pilsicainide, but not by flecainide. The RAFZ, FAZ and CDZ decreased in the P-group (21 +/- 25 msec to 4 +/- 10 msec; p < 0.01, 24 +/- 24 msec to 14 +/- 18 msec; p < 0.05, 56 +/- 29 msec to 43 +/- 32 msec, p < 0.05, respectively), but not in the F-group.

CONCLUSIONS

The effects of atrial conduction delays may differ between pilsicainide and flecainide. Further examination will be needed to explain this mechanism.

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.

Pilot study: Noninvasive monitoring of oral flecainide's effects on atrial electrophysiology during persistent human atrial fibrillation using the surface electrocardiogram

BACKGROUND

The relation between flecainide's plasma level and its influence on human atrial electrophysiology during acute and maintenance therapy of atrial fibrillation (AF) is unknown. Therefore, this study determined flecainide plasma levels and atrial fibrillatory rate obtained from the surface ECG during initiation and early maintenance of oral flecainide in patients with persistent lone AF and assessed their relationship.

METHODS AND RESULTS

In 10 patients (5 males, mean age 63 +/- 14 years, left atrial diameter 46 +/- 3 mm) with persistent lone AF, flecainide was administered as a single oral bolus (day 1) followed by 200-400 mg/day (days 2-5). The initial 300 mg flecainide bolus resulted in therapeutic plasma levels in all patients (range 288-629 ng/ml) with no side effects. Flecainide plasma levels increased on day 3 and remained stable thereafter. Day 5 plasma levels were lower (508 +/- 135 vs 974 +/- 276 ng/ml, P = 0.009) in patients with daily mean flecainide doses of 200 mg compared to patients with higher maintenance doses. Fibrillatory rate obtained from the surface electrocardiogram measuring 378 +/- 17 fpm at baseline was reduced to 270 +/- 18 fpm (P < 0.001) after the flecainide bolus but remained stable thereafter. Fibrillatory rate reduction was independent of flecainide plasma levels or clinical variables.

CONCLUSION

A 300 mg oral flecainide bolus is associated with electrophysiologic effects that are not increased during early maintenance therapy in persistent human lone AF. In contrast to drug plasma levels, serial analysis of fibrillatory rate allows monitoring of individual drug effects on atrial electrophysiology.

Simultaneous determination of serum flecainide and its metabolites by using high performance liquid chromatography

Simultaneous determination of serum flecainide and its oxidative metabolites was carried out by using high performance liquid chromatography (HPLC) equipped with conventional octadecylsilyl silica (ODS) column and fluorescence detector. Flecainide and its metabolites, m-O-dealkylated flecainide (MODF) and m-O-dealkylated lactam of flecainide (MODLF) in serum were extracted with ethyl acetate. The recoveries of flecainide, MODF and MODLF were greater than 92, 93, and 60% with the coefficient of variations (CVs) less than 3.2, 5.8, and 5.3%, respectively. The calibration curves were linear at the concentration range of 50-1500 ng/mL for flecainide and 10-500 ng/mL for MODF and MODLF (r > 0.999). The CVs for intra-day assay were 2.7-5.3% for flecainide, 3.0-4.2% for MODF, and 3.7-4.3% for MODLF, respectively. The CVs for inter-day assay were 7.0-8.4% for flecainide, 3.3-6.7% for MODF, and 4.4-7.7% for MODLF, respectively. This assay method can be used for assessing the metabolic ability of flecainide in the patients with tachyarrhythmia.

Liquid chromatographic determination of unbound flecainide in therapeutic drug monitoring

An assay method was developed for determining unbound flecainide in serum by reversed phase-high performance liquid chromatography (HPLC). Serum water including unbound flecainide was separated by ultrafiltration of the serum sample and subjected to C(18)-cartridge extraction followed by HPLC analysis. The recovery of flecainide from serum water was greater than 93%. The coefficient variations for intra- and inter-day assay of flecainide were smaller than 2.4 and 3.7%, respectively. We applied the method to determining unbound flecainide in serum samples collected from 20 patients receiving oral flecainide (150-300 mg/day) for tachyarrhythmia. Total and unbound concentrations for serum flecainide were 403.5+/-200.8 ng/ml and 180.2+/-95.0 ng/ml, respectively. Linear relationship was observed between total and unbound concentrations (r=0.978, P<0.0001). Percent unbound (44.3+/-5.7%) determined in the present study agreed with the reported values. The percentage unbound tended to increase in the samples with lower alpha(1)-acid glycoprotein (<60 mg/dl). The assay method can be applied to routine determination of unbound flecainide in therapeutic drug monitoring.

Therapeutic monitoring of class I antiarrhythmic agents using high-resolution electrocardiography instead of blood samples

Antiarrhythmic therapy requires monitoring of serum drug concentrations to determine a patient's optimal oral dose of medication. Repeated examination of blood samples, however, is costly and time-consuming, so the present study evaluated whether changes in serum concentrations could be estimated from changes in electrocardiographic (ECG) parameters. Of 36 patients receiving antiarrhythmic drugs for supraventricular or ventricular arrhythmias, 12 were treated with flecainide, 12 with pilsicainide, and 12 with pirmenol. Signal-averaged ECG (SAECG) were recorded before starting drug administration, 1 month later, and twice during ongoing therapy. At the time of the 2nd to the 4th recordings, serum concentrations of the drugs were also measured. As previously reported, all agents, but especially flecainide and pilsicainide, prolonged the filtered QRS (f-QRS) and the duration of low-amplitude signals at the terminal portion of the QRS complex. The SAECG parameters varied between the recordings made during therapy. Differences in the duration of the f-QRS between 2 recordings correlated significantly with differences in serum drug concentrations (r=0.91 for flecainide, r=0.70 for pilsicainide, and r=0.61 for pirmenol). No significant correlation between drug concentration and other SAECG parameters was found. Changes in the serum concentration of flecainide, pilsicainide and pirmenol can be estimated from changes in the duration of the f-QRS on the SAECG and periodic monitoring of such could help reduce the number of repeat measurements of drug concentrations in blood samples.

High performance liquid chromatography for routine monitoring of serum flecainide

We developed a simple, rapid, and selective assay method for determination of serum flecainide by using solid phase extraction and reversed phase high performance liquid chromatography (HPLC) equipped with ordinary octadecylsilyl silica (ODS) column and ultraviolet (UV) detector. Serum samples spiked with the internal standard were treated by a disposable C(18)-cartridge to extract flecainide. The flecainide and internal standard were separated on ODS column and were detected with an UV detector set at 298 nm. The mobile phase solvent consisting of 0.1 M 1-pentanesulfonic acid sodium salt, acetonitrile, and acetic acid (250:206:2.5 v/v) was used at the flow rate of 1.0 ml/min. The calibration curve for flecainide was linear at the concentration of 50-1500 ng/ml (r=0.9998). The recoveries of flecainide from serum samples were 92-98%. The coefficient of variations (CVs) for intra- and inter-day assay were 1.3-4.8 and 3.2-6.9%, respectively. The method could be applied to routine monitoring of serum flecainide in the patients with tachyarrhythmia.

Pharmacokinetics and electrocardiographic effects of a new controlled-release form of flecainide acetate: comparison with the standard form and influence of the CYP2D6 polymorphism

OBJECTIVES

Our objectives were study the single- and repeated-dose pharmacokinetics and electrocardiographic effects (QRS duration) of a new controlled-release form of flecainide acetate compared with the immediate-release form and to examine the influence of CYP2D6 activity.

METHODS

Twenty-four healthy subjects (6 men and 6 women at both dosages) received single and repeated doses of 100 or 200 mg immediate-release and controlled-release flecainide in a randomized crossover design. Electrocardiograms were recorded and flecainide plasma concentrations were measured before administration and up to 96 hours after administration.

RESULTS

The controlled-release formulation had sustained-release properties, with a significantly lower maximum concentration (C(max)) and delayed time to reach C(max). Compared with the immediate-release formulation, the relative bioavailability of the controlled-release formulation at steady state was 0.85 +/- 0.17 and 0.89 +/- 0.17 for the 100-mg/day and 200-mg/day doses, respectively. Trough flecainide plasma concentration at steady state was bioequivalent for both formulations. Maximum and minimum QRS increases were not significantly different for either the immediate-release or the controlled-release form of flecainide after administration of both single and repeated doses. Mean QRS duration during a dosing interval at steady state correlated with mean plasma concentration for both forms (pooled data; P <.001). The 95% confidence interval for this regression was 26% narrower for the controlled-release form than for the immediate-release form. Flecainide-induced QRS prolongation and pharmacokinetics were not significantly influenced by CYP2D6 activity.

CONCLUSIONS

Flecainide-induced QRS prolongation did not differ between the new controlled-release form and the immediate-release form. Flecainide plasma concentrations associated with the new controlled-release form predicted QRS prolongation with less variability compared with the immediate-release form. The CYP2D6 polymorphism did not appear to influence flecainide disposition kinetics or electrocardiographic effects at steady state.

Determination of oral dosage and pharmacokinetic analysis of flecainide in horses

To determine oral dosage and to evaluate the pharmacokinetics in horses of orally administered flecainide, an antiarrhythmic drug, the correlations between its plasma concentration and PR, QRS and QT intervals in equine electrocardiograms (ECG) were investigated. Six healthy horses were administered a randomly ordered dose of 4 or 6 mg/kg of flecainide acetate. The ECG was monitored (heart rate (HR), PR, QRS, and QT intervals) and blood was taken at timed intervals to measure the plasma flecainide concentrations pre- and post-administration. The maximum plasma concentration reached 1014+/-285 (SD) ng/m/ in 45+/-13 min and 1301+/-400 ng/ m/l in 60+/-37 min for doses of 4 and 6 mg/kg flecainide, respectively. From the pharmacokinetic analysis, clearance rates were 14.6+/-6.4 and 11.7+/-5.2 ml/kg/min and terminal elimination half-lives were 228+/-53 and 304+/-87 min. The QRS and QT intervals increased significantly for both doses following administration, though HR and PR intervals did not change. Plasma flecainide concentrations were significantly correlated with QRS (r=0.935, P<0.001) and QT intervals (r=0.753, P<0.001). In conclusion, plasma concentrations of flecainide for treating equine atrial fibrillation were obtained by oral administration of 4 and 6 mg/kg, and the drug was rapidly eliminated from plasma in horses.

Successful extracorporeal life support in a case of severe flecainide intoxication

OBJECTIVE

To show the effectiveness of emergency extracorporeal membrane oxygenation (ECMO) in treating severe, life-threatening flecainide intoxication.

DESIGN

Case report.

SETTING

Intensive care unit in a quaternary care center.

PATIENT

A patient with electromechanical dissociation after severe flecainide acetate overdose.

INTERVENTION

ECMO.

CASE REPORT

A 30-yr-old male with a history of depression presented after a severe flecainide overdose with plasma concentrations exceeding 20 times the upper boundary of the therapeutic range. At presentation, the patient was in refractory cardiocirculatory collapse and was successfully resuscitated with ECMO. Twenty-six hours later, extracorporeal support could be discontinued and the patient made a full recovery.

CONCLUSION

In patients with severe but potentially reversible cardiac dysfunction attributable to flecainide intoxication, ECMO can maintain cardiac output and vital organ perfusion while allowing time for drug redistribution, metabolism, and clearance.

Normalization of ventricular repolarization with flecainide in long QT syndrome patients with SCN5A:DeltaKPQ mutation

BACKGROUND

The Long QT Syndrome (LQTS) is a genetic channelopathy with life-threatening implications. The LQT3 form of this disease is caused by mutations of the SCN5A sodium-channel gene. A specific mutation, SCN5A:DeltaKPQ, is associated with repetitive reopenings of the sodium channel and prolonged inward current. This dominant inward current is manifest on the electrocardiogram as QT prolongation. Flecainide is a potent blocker of the open sodium channel.

METHODS AND RESULTS

The effect of flecainide on the duration of the QT-interval and the T-wave morphology was systematically evaluated in five male patients age 2-64 years having the SCN5A:DeltaKPQ mutation. After baseline electrocardiograms were obtained, low-dose oral flecainide was administered for 48 hours. Serial electrocardiograms and blood flecainide levels were obtained during flecainide therapy. The QTc interval decreased on average by 104 ms, from a baseline value of 565 +/- 60 ms to 461 +/- 23 ms (P < 0.04) at a mean flecainide level of 0.28 +/- 0.08 mg/L, with shortening of the QTonset interval (P < 0.003) and normalization of T-wave morphology. The effects of flecainide were compared with oral mexiletine in two patients, with flecainide showing greater QTc shortening and more complete normalization of repolarization. No adverse side effects or proarrhythmia were observed with flecainide in this study.

CONCLUSION

Low-dose, oral flecainide consistently shortened the QTc interval and normalized the repolarization T-wave pattern in five LQT3 patients with SCN5A:DeltaKPQ mutation. This preliminary study indicates that low-dose flecainide is a promising therapeutic agent for LQTS patients with the SCN5A:DeltaKPQ sodium channel mutation.

Effect of sodium channel blockers on ST segment, QRS duration, and corrected QT interval in patients with Brugada syndrome

INTRODUCTION

Brugada syndrome is characterized by an ST segment elevation in leads V1-V3 and a high incidence of ventricular fibrillation (VF). A mutation in a cardiac Na+ channel gene, SCN5A, has been linked to Brugada syndrome, and sodium channel blockers have been shown to be effective in unmasking the syndrome when concealed. The aim of this study was to examine the effects of Na+ channel blockers on ST segment elevation, QRS, corrected QT (QTc) interval, and ventricular arrhythmias in patients with Brugada syndrome.

METHODS AND RESULTS

We examined the effects of three different Na+ channel blockers (flecainide, disopyramide, and mexiletine) on the amplitude of the ST segment 20 msec after the end of QRS (ST20), QRS duration, QTc interval measured from 12-lead ECG, and ventricular arrhythmias in 12 Brugada and 10 control patients. Maximum ST20 observed in the V2 or V3 leads under baseline conditions was greater in the Brugada patients than in control patients, whereas QRS duration and maximum QTc interval were no different between the two groups. Flecainide and disopyramide, but not mexiletine, significantly increased maximum ST20 and QRS duration in both groups, although these effects were much more pronounced in the Brugada patients. The increases in ST20 and QRS duration with flecainide were significantly larger than those with disopyramide. An increase of 0.15 mV in ST20 with flecainide separated the two groups without overlap. Ventricular premature complexes developed only with flecainide in Brugada patients (3/12) displaying a marked ST elevation but not widening of QRS.

CONCLUSION

Our findings suggest that Na+ channel blockers amplify existing I(Na) and possibly other ion channel defects, with a potency inversely proportional to the rate of dissociation of the drug from the Na+ channel, thus causing a prominent elevation of the ST segment and, in some cases, prolongation of QRS duration in patients with Brugada syndrome.

Therapeutic drug monitoring of flecainide in serum using high-performance liquid chromatography and electrospray mass spectrometry

High-performance liquid chromatography with electrospray mass spectrometry (LC-MS) was used for analysis of the drug flecainide in serum. The clean-up was performed by solid-phase extraction, and an aromatic ring positional isomer was used as internal standard. Results from method validation on spiked serum samples showed excellent reproducibility; intra- and inter-assay variations (C.V.% and %Bias) were less than 6% within the therapeutic concentration range of the drug (0.2-1.0 microg/ml). Linearity was demonstrated from 0.05 to 2.0 microg/ml. The limit of detection and quantification was 0.025 and 0.05 microg/ml, respectively. Due to the high selectivity of the mass spectrometric detection, no interferences were observed. Results from clinical samples (n=18) from patients in treatment with Tambocor (flecainide acetate) showed excellent correlation with parallel data obtained from a method based on high-performance liquid chromatography (HPLC) with fluorescence detection after liquid/liquid extraction. The chromatographic separation of flecainide and internal standard was improved compared to earlier HPLC methods. The methodology is simple, accurate and requires only 0.25 ml of sample. It is a well suited method for routine therapeutic drug monitoring in a hospital or clinical chemistry laboratory.

Fatal flecainide intoxication

A fatal case attributed to flecainide acetate (Tambocor), a class Ic antiarrythmic drug, is presented. Flecainide was detected by GC/MS in gastric contents, blood and liver as well. The urine analysis revealed the presence of its dealkylated metabolite. Body fluids and tissue concentrations determined by GC/ECD were 7.7 mg/kg in femoral blood, 0.26 mg/kg in bile, 18 mg/kg in liver, 0.17 mg/kg in cerebrospinal fluid, 0.22 mg/kg in brain cortex and 28.9 mg/kg in urine. The total amount of flecainide in gastric contents was about 43 mg. Even taking into account the postmortem redistribution of flecainide, its blood level still remains in the toxic range.

Determination of concentrations of flecainide in human serum by high-performance liquid chromatography on a fluorocarbon-bonded silica gel column

An optimized method for the determination of flecainide in serum is presented. Extraction using a solid-phase C18 column and chromatography on a stabilized fluorocarbon-bonded silica gel column effectively separate flecainide from an internal standard (a positional isomer of flecainide). The HPLC apparatus and conditions were as follows: analytical column, Fluofix 120N; sample solvent, 20 microl; column temperature, 40 degrees C; detector, Shimadzu RF-5000 fluorescence spectrophotometer (excitation wavelength = 300 nm, emission wavelength = 370 nm); mobile phase, 0.06% phosphoric acid containing 0.1% tetra-n-butyl ammonium bromide-acetonitrile (75:25, v/v); flow-rate, 1.0 ml/min. The standard curves for flecainide were linear in the concentration range examined (10-2000 ng/ml). The regression equation was y = 0.08+0.0078x (r = 0.9998). The minimum detectable amount of flecainide was approximately 5 ng/ml. In the within-day study, the precision coefficients of variation were 2.66, 2.18, 2.54, 2.72, 2.88, 2.24, and 3.29% for the 10, 50, 100, 200, 500, 1000, and 1500 ng/ml standards, respectively. The absolute recovery rates of flecainide at each concentrations were 94-100%. The method described provides analytical sensitivity, specificity and reproducibility suitable for both biomedical research and therapeutic drug monitoring.

Improved solid-phase extraction technique for plasma flecainide analysis by high-performance liquid chromatography

A method for analyzing flecainide in plasma was developed and assessed. Based on the use of C18 extraction columns eight or fewer times, the rapid and simple extraction procedure provided consistent, high-efficiency flecainide extraction (>85%). Using reverse-phase, high-performance liquid chromatography with fluorometric detection, flecainide acetate was detectable to approximately 15 ng/ml. Retention times of the internal standard and flecainide were 8.9 to 9.2 and 9.8 to 10.4 minutes, respectively, and short sample preparation and run times enabled results to be delivered within 2 to 3 hours of receiving samples. The assay was linear for the standard range 20 ng/ml to 2 microg/ml (r2 with three standards, >0.999) and delivered a high level of accuracy. Quality control concentrations obtained from eight assays consistently fell within 5% of nominal values (100 ng/ml and 1 microg/ml). Based on four assays, the assay was also reproducible with calculated-between and within-assay coefficients of variation of less than 1% and 3%, respectively. The authors found that the performance of this assay was excellent and that the solid-phase extraction technique was simple, rapid, and cost effective.

Survival in a case of life-threatening flecainide overdose

Flecainide acetate is a potent class Ic anti-arrhythmic drug with major sodium channel blocking actions. On the surface electrocardiogram this results in QTc interval prolongation. Overdose with class Ic drugs (< 0.1% of total intoxications) is uncommon, but management is difficult and the mortality high [1]. Serious flecainide overdose is characterised by ventricular tachyarrhythmias, severe bradycardia and variable degrees of atrioventricular block. This report describes a case of life-threatening flecainide overdose in a previously fit individual, resulting in a combination of cardiac disturbances. The treatment options and management are discussed.

Quantitative determination of disopyramide, verapamil and flecainide enantiomers in rat plasma and tissues by high-performance liquid chromatography

Enantiomers of disopyramide (DP), flecainide (FLC) and verapamil (VP) were extracted from rat plasma and tissues (brain, lung, heart, liver, kidney and muscle), followed by quantitative determination using enantioselective high-performance liquid chromatography with chiral stationary-phase columns. The recoveries of S-(+)- and R-(-)-DP from tissues were higher than 69%, and the within- and between-day coefficients of variation were very low (0.5 - 5.7%). The lower limits of detection in each tissue were less than 289 ng/g tissue. The recoveries of S-(+)- and R-(-)-FLC from tissues were higher than 88%, and the within- and between-day coefficients of variation were 1.2-6.0%. The lower limits of detection in each tissue were less than 37 ng/g tissue. The recoveries of S-(-)- and R-(+)-VP from tissues were higher than 80%, and the within- and between-day coefficients of variation were 0.5-6.2%. The lower limits of detection in each tissue were less than 51 ng/g tissue. The analytical methods established in this study will be suitable for determining the concentrations of the enantiomers of these anti-arrhythmic agents in rat plasma and tissues.

Successful treatment of supraventricular tachycardia with flecainide acetate: a case report

BACKGROUND

Efficacy of flecainide acetate for the treatment of fetal supraventricular tachycardia with cardiac failure was reported.

CASE

For a case in which maternal digoxin therapy failed, flecainide acetate (400 mg/day) is used from 27 weeks. Cardioversion with improved cardiac function occurred 6 days after treatment. Fetal serum flecainide acetate level was 292 ng/ml which was 64% of the maternal level (453 ng/ml). No adverse maternal side effects were noted with 11 weeks of therapy. A vigorous male baby, weighing 3,610 g, Apgar 8/9, Ua-pH 7.24, was born. He is now 1 year of age and in good condition with medication of 5 mg/kg flecainide acetate.

CONCLUSION

Flecainide acetate seemed to be safe for both mother and fetus, and effective for the treatment of fetal supraventricular tachycardia which is refractory to transplacental digoxin therapy.

[Benefit of monitoring the level of blood flecainide acetate in an elderly patient with ventricular premature contractions]

A 67-year-old woman without organic heart, disease had symptomatic ventricular premature contractions. Because class Ia, Ib and IV antiarrhythmic drugs did not prevent the premature contractions, the patient was treated with flecainide acetate at a dose of 50 mg t.i.d. Adverse reactions were noted. After measurement of the blood drug level, the dose was reduced to 50 mg b.i.d. The adverse reactions disappeared, and the arrhythmia was controlled. Flecainide acetate has a relatively long blood elimination half-life and a narrow safety margin. When some antiarrhythmic drugs are used in elderly patients, blood drug level monitoring is useful in preventing adverse reactions and in designing appropriate therapy.

Differences in amiodarone, digoxin, flecainide and sotalol concentrations between antemortem serum and femoral postmortem blood

1. The concentrations of amiodarone/desethylamiodarone, digoxin, flecainide and sotalol were measured in serum collected immediately prior to death and in postmortem blood collected from the femoral vein and artery of an 18-year-old male with congenital heart disease who developed a fatal arrhythmia. 2. The concentrations of all four drugs in the sample collected during life were consistent with the dosage given and in the range accepted for normal therapy. 3. There were no differences in amiodarone/desethylamiodarone, flecainide and sotalol concentrations in arterial or venous postmortem blood. 4. The concentrations of desethylamiodarone, digoxin, flecainide and sotalol but not amiodarone, were higher in postmortem blood than in antemortem serum. The flecainide concentration was significantly greater than the upper limit associated with toxicity in life. Without knowledge of the true concentration measured in life, this apparently high, toxic concentration would have suggested that death could have resulted from arrhythmogenic/proarrhythmic effects of the drug in excess. 5. These results further demonstrate the hazards in interpreting postmortem blood concentrations following suspected drug intoxication.

Intravenous flecainide versus amiodarone for recent-onset atrial fibrillation

In a randomized, double-blind, controlled study of 98 patients with atrial fibrillation (AF) (present for > or = 30 minutes, < or = 72 hours, and a ventricular response of > or = 100 beats/min), intravenous flecainide (2 mg/kg, maximum 150 mg) was compared with intravenous amiodarone (7 mg/kg) and placebo. Exclusion criteria included significant left ventricular dysfunction, inotrope dependence, recent antiarrhythmic therapy, hypokalemia, and pacemaker dependence. Reversion to stable sinus rhythm within 2 hours of starting medication was considered likely to be due to drug effect. Twenty of 34 patients (59%) given flecainide, 11 of 32 (34%) given amiodarone, and 7 of 32 (22%) given placebo reverted to stable sinus rhythm in < or = 2 hours after starting medication (chi-square 9.87, p = 0.007). More patients reverted to stable rhythm with flecainide than with placebo (p = 0.005; odds ratio 5.1, 95% confidence interval 1.54 to 17.5). There was no significant difference between amiodarone and placebo or between flecainide and amiodarone. However, after 8 hours there were no significant differences in reversion between the treatment groups: flecainide (n = 23, 68%), amiodarone (n = 19, 59%), and placebo (n = 18, 56%). Amiodarone promptly reduced the ventricular rate, and this effect was maintained for 8 hours in those whose reversion to stable sinus rhythm was unsuccessful: flecainide was no more effective than placebo in controlling ventricular rate. Adverse effects were not significantly different in the 3 groups. Thus, intravenous flecainide results in earlier reversion of AF than does intravenous amiodarone or placebo. Amiodarone, although less effective in reverting AF, slows the rapid ventricular response.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of the absolute bioavailability of flecainide using stable isotope technique

Data on the absolute bioavailability of flecainide are controversial. We have investigated whether differences in metabolic clearances and/or the absorption profile might be responsible for the variability in its absolute bioavailability. Six subjects with a wide range of flecainide metabolic clearances (85-407 ml.min-1) simultaneously received the drug by the IV and oral routes; the oral dose was labelled with deuterium. Besides estimation of absolute bioavailability, this design permitted assessment of metabolic clearance after IV and oral administration, and absorption could be assessed from the urinary excretion of labelled and unlabelled drug and metabolites. The absolute bioavailability of flecainide ranged from 79.9 to 101.1% (mean 93.6%). The absorption was 86.1 to 101.3% (mean 93.2%). The data indicate that the variable bioavailability of flecainide is due both to metabolism and absorption. The study highlights the potential of stable isotope technique in the investigation of such issues.

Prolongation of intraventricular conduction time associated with fatal [correction of fetal] impairment of defibrillation efficiency during treatment with class I antiarrhythmic agents

To test whether fatal deterioration of defibrillation efficiency during antiarrhythmic therapy can be prevented by avoiding extreme decrease in ventricular prevented by avoiding extreme decrease in ventricular conduction or toxic plasma drug levels, we determined the defibrillation threshold (DFT) before and during infusion of incremental doses of disopyramide (n = 8), mexiletine (n = 9), or flecainide (n = 9) in anesthetized dogs. Disopyramide did not alter DFT [from 4.4 +/- 1.5 to 4.4 +/- 1.6 J (3.1 +/- 1.2 micrograms/ml)]. Mexiletine tended to increase DFT [from 4.6 +/- 1.2 to 6.1 +/- 2.0 J (1.8 +/- 0.6 micrograms/ml); p < 0.05], and defibrillation eventually was unsuccessful in 3 of the 9 dogs. Although the plasma mexiletine level before refractory fibrillation was far beyond the human therapeutic range, prolongation of intraventricular conduction time (CT) was moderate (16 +/- 3%). Flecainide increased DFT from 4.2 +/- 1.3 to 6.1 +/- 1.5 J at a plasma level of 1.04 +/- 0.37 micrograms/ml (p < 0.0005). In 3 of 5 dogs that developed refractory fibrillation, plasma flecainide level before terminal ventricular fibrillation (VF) was not toxic, but prolongation of CT in the 5 dogs was remarkable (30 +/- 9%). Thus, VF resistant to defibrillation is not necessarily associated with both toxic plasma drug level and remarkably decreased conduction. Reliability of these valuables as indicators of fatally deteriorated defibrillation efficiency may vary among antiarrhythmic agents.

Identification of flecainide and lorcainide in blood by means of TLC

New antiarrhythmics-flecainide and lorcainide-extracted from plasma were separated by TLC method on silica gel by ascending development, using suitable mobile phases. The substances were identified by reaction with indicators: Dragendorff reagent for lorcainide (up to the amount 50 ng) and acidified 15% FeCl3, followed by 15% KI and water for flecainide (up to the amount 500 ng).

Flecainide acetate for paroxysmal supraventricular tachyarrhythmias. The Flecainide Supraventricular Tachycardia Study Group

Flecainide has been shown to be effective in short-term, controlled studies for prevention of paroxysmal supraventricular tachycardia (SVT) and paroxysmal atrial fibrillation (AF). However, it is unknown whether this beneficial response is maintained during long-term chronic therapy. Forty-nine patients were studied who enrolled in double-blind, placebo-controlled, short-term studies of safety and efficacy and subsequently received long-term, open-label therapy for > or = 6 months (mean duration of therapy, 17 months). To evaluate chronic efficacy, events during long-term therapy were documented by a transtelephonic monitor for either 4 or 8 weeks, comparable to the corresponding 4- or 8-week placebo-baseline periods in the same patients. Results during chronic therapy were compared with those at baseline and after the initial (short-term) treatment period. Compared with placebo-baseline results, the number of patients free of arrhythmic attacks increased significantly for both patients with SVT (from 24% to 82%, p = 0.013, n = 17) and patients with AF (from 12% to 68%, p < 0.001, n = 25). Mean time to first attack and mean number of days between attacks also showed significant and parallel increases during the chronic efficacy period. In patients with paired short- and long-term efficacy evaluations with the same dose of flecainide, end points were maintained at equivalent levels or showed further improvement (i.e., mean rate of AF attacks decreased further with chronic therapy, p = 0.036). No proarrhythmic events, death, or myocardial infarction occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Unpredictability of flecainide plasma concentrations in patients with renal failure: relationship to side effects and sudden death?

We report a retrospective evaluation of plasma concentrations of flecainide obtained from five dialysis patients during chronic oral treatment. A more than sevenfold variation in the dose/concentration relationship was observed. Plasma concentrations of flecainide above 1,200 ng/ml appeared to be associated with serious side effects and in one case with sudden death. Therefore, flecainide should be used with extreme caution in patients with impaired renal function. Frequent therapeutic drug monitoring should be mandatory.

Comparative haemodynamic effects of verapamil, flecainide, amiodarone and sotalol in the conscious rabbit

1. The effect of intravenous boluses of verapamil (0.15 mg/kg), flecainide (2 mg/kg), amiodarone (5 mg/kg), and sotalol (1.5 mg/kg) on mean arterial pressure, heart rate (HR), cardiac output (CO), total peripheral resistance (TPR), and peak rate of change of left ventricular pressure (LV dP/dt) were assessed in the conscious rabbit. 2. All four drugs had negative inotropic effects: verapamil reduced peak LV dP/dt by 19 +/- 4% (mean +/- s.e.m.; P < 0.01), flecainide by 27 +/- 9% (P < 0.001), amiodarone by 11 +/- 2% (P < 0.01) and sotalol by 13 +/- 3% (P < 0.01). 3. The drugs had different effects on CO as a result of differences in their actions on peripheral blood vessels: verapamil and amiodarone produced, respectively, a 12 +/- 4% (P < 0.03) and 16 +/- 6% (P < 0.01) increase in CO associated with a substantial vasodilatory effect (TPR reduced 15 +/- 7% [P < 0.05] and 20 +/- 5% [P < 0.01], respectively). Flecainide caused only a small (6 +/- 1%; P < 0.01) increase in CO and sotalol had no effect on either CO or TPR. 4. Bolus intravenous injections of verapamil, flecainide and amiodarone produced an increase in HR, while sotalol reduced HR by 10 +/- 2% (P < 0.01). The increase in HR and cardiac output seen with verapamil, flecainide and amiodarone was in part secondary to reflex increase in sympathetic tone and these changes were abolished after total cardiac autonomic blockade. 5. The modest reduction in cardiac performance associated with sotalol was abolished by cardiac autonomic blockade, suggesting that the predominant effect of sotalol on contractility was mediated through its beta-adrenoceptor blocking effect.

Influence of age and gender on the in vitro serum protein binding of flecainide

The in vitro protein binding of flecainide was studied by equilibrium dialysis in relation to serum concentrations of albumin and alpha 1-acid glycoprotein (AAG) in 22 healthy subjects of both sexes aged between 23 and 89 years. In the range of flecainide concentrations tested, protein binding of flecainide was not saturable and the percent value of the unbound fraction ranged between 0.48 and 0.68, mean value (SD) = 0.59 (+/- 0.06), without any significant difference between males and females or between young and old subjects. The flecainide unbound fraction was significantly correlated with serum albumin concentrations but not with total serum proteins or AAG concentrations.

Comparison of fluorescence polarisation immunoassay (FPIA) and high performance liquid chromatography (HPLC) methods for the measurement of flecainide in human plasma

The precision and accuracy of HPLC and FPIA for the measurement of flecainide plasma levels were compared below, in and above the therapeutic range (200-1,000 ng/ml). Following a calibration crossover study, five standard plasma solutions of varying flecainide concentrations (SPS) and 99 flecainide containing plasma samples of 24 in-patients (IPS) were analyzed with both methods. The results show that within the range of approximately 500-1,500 ng/ml, the two methods did not differ in either precision (expressed as coefficient of variation, CV) or accuracy (expressed as relative error, RE). Close to the lower limit and below the therapeutic range however, HPLC provided greater precision and accuracy than FPIA.

Pharmacodynamic variability of flecainide assessed by QRS changes

The effect of flecainide on the QRS interval was studied in 10 patients who were receiving long-term oral treatment (50 to 150 mg twice daily) for arrhythmias that were refractory to other drugs. Total and free drug plasma levels and QRS durations were measured at intervals after the morning administration. Free drug plasma levels were linearly correlated with QRS duration in each patient and the slope of the line was widely variable in the population studied. Even after the data from one patient with an unusually high slope (0.454) was excluded from the analysis, the slope range was 0.0284 to 0.144. Pharmacodynamic variability could not be explained by heart rate changes, active metabolites, electrolyte disturbances, or free drug concentration. None of the pharmacokinetic parameters measured (average steady-state concentration, fluctuation of maximum and minimum concentrations, time to peak concentration, final half-life, and protein binding) showed an intersubject variability greater than 4.4 times. Our findings suggest that the determination of flecainide free plasma concentration may not be sufficient to forecast electrophysiologic effects in individual patients.

Application of the Empore solid-phase extraction membrane to the isolation of drugs from blood: II. Mexiletine and flecainide

A stabilized therapeutic drug monitoring procedure incorporating the novel Empore solid-phase extraction membrane (SPEM) for isolation of the antiarrhythmic drugs mexiletine (MEX) and flecainide (FLEC) from serum is described. Routinely, serum (0.5 ml), adjusted to pH 4.5, is passed through an octyl (C8) SPEM to extract the drugs. A methanol:water wash follows to remove proteins and interferences. MEX and FLEC are eluted from the membrane with mobile phase and an aliquot is injected directly onto a Zorbax cyanopropyl (CN) high-performance liquid chromatographic column with detection at 214 nm. Evaporating/concentrating techniques that can adversely influence the stability of the volatile MEX are unnecessary. Recovery for both drugs exceeds 90% and the assay is linear from 0.05 mg/L up to at least 6.0 mg/L for MEX and from 0.05 mg/L up to at least 3.0 mg/L for FLEC. Precision (between-run) coefficients of variation range from 2.3 to 3.0% (0.49-1.97 mg/L) for MEX and 3.7 to 5.9% (0.240-0.992 mg/L) for FLEC. Interferences are minimal. When we compared performance of the Empore SPEM and large-particle solid-phase sorbents packed in cartridges, we observed greater capacity per gram of sorbent and smaller elution volume with the membrane. Most important, concentrating steps that adversely affect the stability of MEX are avoided with the SPEM.

Effects of flecainide on the rate dependence of atrial refractoriness, atrial repolarization and atrioventricular node conduction in anesthetized dogs

Flecainide is effective against certain supraventricular arrhythmias (atrial fibrillation and atrioventricular [AV] node reentrant tachycardia), but its mechanisms of action are unknown. Previous in vitro work suggests that flecainide attenuates rate-dependent action potential duration shortening, producing tachycardia-dependent prolongation of the refractory period. This study was designed to assess whether similar changes occur in vivo and whether the effects of flecainide on AV node conduction depend on heart rate and on direction of propagation (anterograde vs. retrograde). The effects of flecainide at three clinically relevant concentrations were assessed in open chest, morphine-chloralose-anesthetized dogs. Flecainide increased atrial refractory period in a concentration- and rate-related fashion (e.g., dose 3 increased the atrial effective refractory period by 9 +/- 4% at a cycle length of 1,000 ms but by 36 +/- 5% and 55 +/- 10% at a basic cycle length of 400 and 300 ms, respectively; p less than 0.001 for each). Flecainide attenuated the action potential duration accommodation (measured by monophasic action potentials) to heart rate, causing tachycardia-dependent action potential duration prolongation and accounting for most of the rate-dependent atrial effective refractory period changes. Flecainide increased Wenckebach cycle length, but the concentration-response curve was much steeper in the retrograde (slope 41 +/- 7 ms/mumol.liter-1) than in the anterograde direction (17 +/- 4 ms/mumol.liter-1; p less than 0.01), indicating more potent effects on retrograde conduction. The depressant action of the drug on the AV node was also rate dependent, with an effect on the AH interval at a basic cycle length of 400 ms that averaged 1.8, 1.5 and 2 times that at a basic cycle length of 1,000 ms for doses 1 (p less than 0.05), 2 (p less than 0.01) and 3 (p less than 0.001), respectively.

CONCLUSIONS

1) Flecainide suppresses atrial action potential duration accommodation to heart rate changes in vivo, leading to rate-dependent atrial effective refractory period prolongation, which may be important in suppressing atrial fibrillation. 2) The drug has frequency- and direction-dependent effects on AV node conduction, which may lead to selective antiarrhythmic actions during AV node reentry.

Arrhythmogenic activities of antiarrhythmic drugs in conscious hypokalemic dogs with atrioventricular block: comparison between quinidine, lidocaine, flecainide, propranolol and sotalol

In order to create and evaluate a model sensitive to QT-dependent proarrhythmic effects of drugs, a long QT syndrome was produced in chronically instrumented dogs with bradycardia and hypokalemia. Bradycardia (mean cycle length: 1495 +/- 78 msec) was provided by permanent atrioventricular block and hypokalemia (K+ = 2.6 +/- 0.05 mmol/l) by high doses of diuretics. To evaluate that model, six of these conscious dogs were subjected to quinidine, flecainide, lidocaine, propranolol and sotalol infusions. In crossover design, drugs were infused i.v. at rates allowing stable and nontoxic drug plasma levels during the experiment. Four-lead ECGs were recorded for arrhythmias for 30 min before (base line) and 75 min after onset of infusion. Ventricular cycle length was increased dramatically by sotalol, lidocaine and propranolol (+618 +/- 192, +388 +/- 125 and +329 +/- 114 msec, respectively) and QT interval was increased by sotalol, quinidine and flecainide (+56 +/- 8, +31 +/- 7.9 and +20 +/- 5.7 msec, respectively). Quinidine and sotalol, but not flecainide, propranolol or lidocaine, exhibited significant arrhythmogenic activities. During quinidine infusion, most dogs exhibited some ventricular arrhythmias whose most severe forms were runs of ventricular tachycardia. These arrhythmias were suppressed by pacing at high rates. During sotalol infusion, five out of six dogs exhibited typical "torsades de pointes." This incidence was not related to the slowing effects of sotalol on idioventricular pacemakers, because a similar incidence was obtained in five complementary dogs paced at 40 bpm. It could be related to dose, because torsades de pointes occurred only once in another group of five dogs receiving half the dose used in the controlled study. Only quinidine and sotalol, but not propranolol, flecainide or lidocaine, are clinically associated to torsades de pointes. They were also the only drugs associated with proarrhythmic events in the present study, a fact suggesting that QT-dependent arrhythmogenic effects of drugs can be reliably evaluated in conscious hypokalemic dogs with complete atrioventricular block.

A high performance liquid chromatographic method for the quantitation of flecainide in plasma

A routine high performance liquid chromatographic method for the rapid determination of flecaïnide (Flecaine), using a novel internal standard, N-methylflecaïnide, has been developed. After deproteinization of spiked samples, flecaïnide was totally recovered at neutral pH. Flecaïnide and the internal standard were separated on a reversed phase XL 3 microns ODS column using 10 mM phosphate buffer, pH 3.0: acetonitrile (70:30) as mobile phase, in less than 10 min. With spectrofluorometric detection, the limit of quantitation for flecaïnide was 10 ng/mL. Intra- and inter-assay precision variations were 0.24% and 1.4%.

[Use of flecainide in the preventive treatment of tachycardia crisis of Wolff-Parkinson-White syndrome in 4 newborn infants]

Four neonates with Wolff-Parkinson-White syndrome developed supraventricular tachycardia and received flecainide orally after reduction of the arrhythmia. The initial doses were 5 mg/kg/day. They are increased according to clinical response and flecainide concentrations, with 5 and 10 mg/kg/24 h respectively, were in the therapeutic range of 200 to 1000 micrograms/l. Flecainide was effective and well tolerated in the 4 cases. Therefore, this drug may be an alternative to digoxine to prevent supraventricular tachycardias in the neonatal period.

Relationship between serum concentrations of flecainide and fluoride in humans

The biotransformation of flecainide to serum fluoride after the oral administration of 100 mg to six healthy subjects was studied. Fluoride, flecainide acetate, calcium and alkaline phosphatase serum levels were determined at 0, 3, 4.5 and 6 hours after administration. Higher mean serum concentrations for fluoride and alkaline phosphatase (P less than 0.01, P less than 0.005) and lower mean calcium levels (P less than 0.05) were reached at 4.5 hours. The flecainide acetate serum levels ranged from 108 to 261 ng/ml. The results were analyzed for statistical significance by single factor analysis of variance with repeated measures. The Spearman rank correlation coefficient between flecainide acetate and fluoride serum increases was calculated. Our results would suggest that fluorine-containing flecainide could be biotransformed to yield some ionic fluoride which contribute to the daily fluoride intake.