Flecainide: evidence of non-linear kinetics

Review on Flecainide Poisoning

Flecainide acetate is a Vaughn-Williams class IC antiarrhythmic. It is used mainly for treatment of supraventricular arrhythmias due to reentry and is highly effective in suppressing frequent premature ventricular depolarization and nonsustained ventricular tachycardia (VT). Although less than 1% of drug overdoses are fatal, severe intoxication with Vaughn-Williams class IC antiarrhythmics is associated with average mortality of 22.5% and the rate of mortality after flecainide overdose is approximately 10%. Severe flecainide overdose is frequently fatal because of the rapid onset of hypotension and ventricular arrhythmias. Its cardiotoxicity is mainly due to its sodium and potassium channels blocking effects. Commonly recommended therapies like haemolysis or haemoperfusion is not helpful because of its large volume of distribution. As a result, the treatment goals are to decrease the amount of blockade; correct aggravating conditions for arrhythmias, such as electrolytes disturbances or hypoxia; avoid drugs with sodium channels blocking effects. Recently, there are some successful data on using peripheral cardiopulmonary bypass technique in the treatment of severe flecainide intoxication. This may be a promising treatment option in this type of drug overdose.

Flecainide-induced Increase in QRS Duration and Proarrhythmia during Exercise

In patients taking flecainide, exercise-induced arrhythmias are believed to be related to QRS widening at rest and during exercise. Our aim was to determine, retrospectively, predictive factors of flecainide-induced (a) QRS widening at rest and during exercise, and (b) proarrhythmia (PA) during exercise. Flecainide was administered to 119 patients for atrial and/or ventricular arrhythmias who performed a maximal treadmill test. A total of 63 patients had a normal heart (defined by the absence of structural heart disease and an ejection fraction ≥ 55% by echocardiography and/or cardiac catheterisation), 26 had coronaropathy, 18 valvulopathy and 3 had both, and 7 had dilated and 2 hypertrophic cardiomyopathy. The mean dosage of flecainide was 190 or 200 ± 10 mg/day. Previous myocardial infarction (MI) was a predictive variable of flecainide-induced QRS widening at rest (p = 0.04). During exercise, the risk factors of QRS widening were previous MI (p = 0.008), angina without previous MI (p = 0.009), structural heart disease (p = 0.001) and a bundle branch block at rest (p = 0.01). PA on exercise occurred in 7 patients. Structural heart disease (p = 0.04) and an impaired left ventricular ejection fraction (LVEF) [p = 0.02] were predictive variables of PA. All patients with left ventricular dysfunction and PA had a QRS widening with flecainide at rest ≥ 25%. The risk factors of QRS widening at rest and during exercise with flecainide were distinct from those of PA on exercise. In patients with an impaired LVEF, a flecainide-induced QRS widening of 25% at rest was the threshold value beyond which there was a high risk of PA during exercise. This study was retrospective and not a double-blind trial, therefore the results need to be corroborated in a prospectively designed trial.

Serum flecainide S/R ratio reflects the CYP2D6 genotype and changes in CYP2D6 activity

The aims of this study were to clarify whether the ratio of S- to R-flecainide (S/R ratio) in the serum flecainide concentration was associated with the stereoselectivity of flecainide metabolism, and to investigate the effects of the cytochrome P450 (CYP) 2D6 (CYP2D6) genotype and CYP2D6 inhibitor on the serum flecainide S/R ratio. In vitro studies using human liver microsomes and cDNA-expressed CYP isoforms suggested that variability in the serum flecainide S/R ratio was associated with the stereoselectivity of CYP2D6-mediated flecainide metabolism. We examined the serum flecainide S/R ratio in 143 patients with supraventricular tachyarrhythmia. The S/R ratio was significantly lower in intermediate metabolizers and poor metabolizers (IMs/PMs) than in extensive metabolizers (EMs) identified by the CYP2D6 genotype. The cut-off value for the S/R ratio to allow the discrimination between CYP2D6 EMs and IMs/PMs was 0.99. The S/R ratio in patients with co-administration of bepridil, a potent CYP2D6 inhibitor, was lower than 0.99, regardless of the CYP2D6 genotype status. Other factors, including age, sex, body weight, and renal function, did not affect the serum flecainide S/R ratio. This study suggests that the serum flecainide S/R ratio reflects the CYP2D6 genotype and changes in CYP2D6 activity on co-administration of a CYP2D6 inhibitor.

Safety of flecainide

Flecainide is a class Ic antiarrhythmic agent that has an important role as part of rhythm control strategies in patients with atrial fibrillation (AF). Early clinical data on the use of flecainide showed an increase in arrhythmias and mortality compared with placebo in patients with a previous myocardial infarction and asymptomatic or mildly symptomatic ventricular arrhythmias. These findings only apply to a specific group of patients with left ventricular dysfunction and ischaemic heart disease, but had a negative impact on the use of class Ic antiarrhythmics across all indications and patient groups. The aim of this review was to evaluate the available safety data for flecainide in the literature and to assess its current use in patients with AF. Current European guidelines now recommend the use of flecainide in carefully selected groups of patients with AF who do not have structural heart disease. This includes for the cardioversion of recent-onset AF, pretreatment prior to direct current cardioversion, out-of-hospital acute oral therapy ('pill-in-the-pocket' approach) and for the ongoing maintenance of sinus rhythm. Potential cardiac adverse effects of flecainide include proarrhythmia, conduction abnormalities and negative inotropic effects. Dizziness is the most frequent non-cardiac side effect, followed by blurred vision and difficulty focusing; these are almost all mild, transient and tolerable. Data from recent clinical trials in patients with supraventricular arrhythmias suggest that flecainide has a good tolerability profile in groups of appropriately selected patients. Caution is required when using flecainide in patients with renal dysfunction, and there are a number of drug interactions, but these are well documented and manageable. Overall, flecainide is a good choice for the pharmacological management of AF. It has a good safety record and low incidence of adverse effects, rare end-organ toxicity and a low risk of ventricular proarrhythmia. To ensure that the benefits of treatment outweigh any potential risks, careful patient selection and monitoring is required.

Pharmacokinetic interaction of flecainide and paroxetine in relation to the CYP2D6*10 allele in healthy Korean subjects

AIMS

The objectives were to evaluate the effect of CYP2D6 genetic polymorphism on the pharmacokinetics of flecainide, and also on the extent of drug interaction with paroxetine as a CYP2D6 inhibitor after a single oral administration in healthy subjects.

METHODS

An open-label, two-period, single-sequence, cross-over study was performed in 21 healthy Korean male volunteers (seven for CYP2D6*1/*1 or *1/*2, group 1; seven for CYP2D6*1/*10, group 2; seven for CYP2D6*10/*10 or *10/*36, group 3). Subjects were administered 200 mg of flecainide on day 1. After a 7-day wash-out period, subjects were administered 20 mg of paroxetine from day 8 to 14, and 200 mg of flecainide on day 15. Blood sampling was performed up to 72 h after flecainide administration.

RESULTS

Terminal elimination half-life and mean residence time (MRT) were significantly different among three genotype groups after a single oral administration of flecainide (P = 0.021, 0.011, respectively). Area under the concentration-time curve, terminal elimination half-life and MRT increased significantly after paroxetine co-administration only in groups 1 and 2.

CONCLUSIONS

This study reports that the extent of drug interaction between flecainide and paroxetine is influenced by the CYP2D6*10 allele in healthy subjects, which is frequent in Asians.

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.

Measurement of flecainide in hair as an index of drug exposure

We report a method for measuring the concentration of flecainide in hair. An animal study, in which flecainide (1, 5, and 10 mg/kg/day) was orally administered for 1, 2, and 3 weeks to pigmented rats, showed that flecainide concentration in rat hairs newly regrown after administration significantly correlated with both the daily dose and the dosing period. The part of hair containing flecainide continued to grow upward, retaining the drug within the hair structure that had been formed at the time of drug exposure. Flecainide was also determined in human scalp hairs collected from patients treated with flecainide. The drug content of white hairs was much less than that black hairs collected from the same rats and subjects, suggesting the determinant effect of hair pigment on flecainide accumulation in hair. These findings suggest that the analysis of flecainide in hair may be useful for assessing exposure to drug qualitatively.

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.