Minimal effective concentration values of propafenone and 5-hydroxy-propafenone in acute and chronic therapy

Effect of CYP2D6 polymorphisms on the pharmacokinetics of propafenone and its two main metabolites

AIM OF THE STUDY

Propafenone (PPF) is an antiarrhythmic drug, metabolized mainly by CYP2D6 to 5-hydroxypropafenone (5OH-PPF) and by CYP3A4 to norpropafenone (NOR-PPF). CYP2D6 shows a high degree of genetic polymorphism which is associated with diminished antiarrhythmic efficacy or cardiac seizures/cardiotoxicity. This study aimed to investigate the effect of the CYP2D6 polymorphism on the pharmacokinetics of PPF and its two main metabolites. The usefulness of PPF/5OH-PPF ratio for CYP2D6 phenotyping in healthy adults was also evaluated.

METHODS

Twelve healthy volunteers, 3 poor metabolizers (PM), 2 intermediate metabolizers (IM) and seven extensive metabolizers (EM) received an oral dose of PPF. Concentrations of PPF and its metabolites were analyzed in serum samples over 27h.

RESULTS

The PPF/5OH-PPF ratio distinguished EMs from PMs, but not from IMs. In PMs, the mean transit time (MTT) values were almost the same for PPF and NOR-PPF and much higher than those of EMs and IMs. 5OH-PPF was not detected in EMs. Mean MTT values of 5OH-PPF and NOR-PPF in IMs were 5.27- and 1.52-fold higher than those of EMs.

CONCLUSION

A single time point serum PPF-MR approach is a useful tool to identify PMs. CYP2D6 polymorphism significantly affects the pharmacokinetics of PPF and its two metabolites.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Pharmacogenetics, drug-metabolizing enzymes, and clinical practice

The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.

Outpatient treatment of recent-onset atrial fibrillation with the "pill-in-the-pocket" approach

BACKGROUND

In-hospital administration of flecainide and propafenone in a single oral loading dose has been shown to be effective and superior to placebo in terminating atrial fibrillation. We evaluated the feasibility and the safety of self-administered oral loading of flecainide and propafenone in terminating atrial fibrillation of recent onset outside the hospital.

METHODS

We administered either flecainide or propafenone orally to restore sinus rhythm in 268 patients with mild heart disease or none who came to the emergency room with atrial fibrillation of recent onset that was hemodynamically well tolerated. Of these patients, 58 (22 percent) were excluded from the study because of treatment failure or side effects. Out-of-hospital self-administration of flecainide or propafenone--the "pill-in-the-pocket" approach--after the onset of heart palpitations was evaluated in the remaining 210 patients (mean age [+/-SD], 59+/-11 years).

RESULTS

During a mean follow-up of 15+/-5 months, 165 patients (79 percent) had a total of 618 episodes of arrhythmia; of those episodes, 569 (92 percent) were treated 36+/-93 minutes after the onset of symptoms. Treatment was successful in 534 episodes (94 percent); the time to resolution of symptoms was 113+/-84 minutes. Among the 165 patients with recurrences, the drug was effective during all the arrhythmic episodes in 139 patients (84 percent). Adverse effects were reported during one or more arrhythmic episodes by 12 patients (7 percent), including atrial flutter at a rapid ventricular rate in 1 patient and noncardiac side effects in 11 patients. The numbers of monthly visits to the emergency room and hospitalizations were significantly lower during follow-up than during the year before the target episode (P<0.001 for both comparisons).

CONCLUSIONS

In a selected, risk-stratified population of patients with recurrent atrial fibrillation, pill-in-the-pocket treatment is feasible and safe, with a high rate of compliance by patients, a low rate of adverse events, and a marked reduction in emergency room visits and hospital admissions.

Oral loading with propafenone for conversion of recent-onset atrial fibrillation: a review on in-hospital treatment

Atrial fibrillation (AF) is a very common arrhythmia. In order to treat acute AF rapidly, effective drug regimens are required. Propafenone is a class IC antiarrhythmic agent that is suitable for oral loading as it reaches peak plasma concentrations within 2 to 4 hours of administration. The use of propafenone loading in patients with AF must be based on appropriate patient selection in view of the negative inotropic effect and the potential proarrhythmic effects of the drug. A series of controlled trials in patients with recent-onset AF without heart failure who were hospitalised with enforced bed rest has shown that orally loaded propafenone (450 to 600 mg as single dose) exerts a relatively quick effect (within 3 to 4 hours) and a high rate of efficacy (72 to 78% within 8 hours). A potentially harmful effect of class IC agents is the risk of transforming AF into atrial flutter (3.5 to 5% of patients). However, atrial flutter with 1 : 1 atrioventricular response was observed in only two of 709 patients receiving propafenone (0.3% incidence). Nevertheless, the potential negative inotropic effect of propafenone demands careful patient selection, with systematic exclusion of patients with left ventricular dysfunction or congestive heart failure. Oral loading with propafenone can be considered as an episodic treatment in patients with AF recurrences, as has been proposed for other drugs in the past. However, the safety of oral loading with propafenone as an outpatient treatment in appropriately selected patients has to be assessed by appropriately designed prospective studies.

Single oral loading dose of propafenone for pharmacological cardioversion of recent-onset atrial fibrillation

The efficacy and safety of the single dose oral loading regimen of propafenone for pharmacological cardioversion of recent-onset atrial fibrillation (AFib) was evaluated by analyzing the trials on the subject identified through a comprehensive literature search. Most of the trials used a single dose of 600 mg for oral loading. The success rates ranged from 56% to 83%, depending on the duration of AFib and follow-up after drug administration. The conversion time ranged from 110 +/- 59 to 287 +/- 352 min, depending on the duration of observation after drug administration. The single dose oral loading regimen of propafenone was significantly more efficacious than placebo in the first 8 h after administration but not at 24 h. Compared with the intravenous regimen, the oral regimen resulted in fewer conversions in the first 2 h, but both regimens were equally efficacious afterward. The oral propafenone regimen was as efficacious as the single dose oral loading regimen of flecainide but was superior to those of quinidine and amiodarone. The adverse effects reported were transient arrhythmia, reversible QRS-complex widening, transient hypotension and mild noncardiac side effects. The transient arrhythmias were chiefly at the time of conversion and included appearance of atrial flutter, bradycardia, pauses and junctional rhythm. No life-threatening proarrhythmic adverse effects were reported. The single oral loading dose of propafenone appears to be highly effective for conversion of recent-onset AFib, with a relatively rapid effect within 2 to 3 h and freedom from serious adverse effects.

Safety of oral propafenone in the conversion of recent onset atrial fibrillation to sinus rhythm: a prospective parallel placebo-controlled multicentre study

AIM

Oral propafenone is effective in restoring sinus rhythm however the proarrhythmic effects are still unknown. The Safety Antiarrhythmic Therapy Evaluation (SATE) trial was a prospective randomized placebo-controlled multicentre study which evaluated the safety of acute oral loading dose of propafenone in patients with recent onset atrial fibrillation. Secondary end-points were to evaluate the effect of digitalis added to propafenone in ventricular rate control and the efficacy of propafenone alone or added to digitalis compared with efficacy of digitalis plus quinidine.

METHODS AND RESULTS

246 patients (126 male; 58+/-11 years) with atrial fibrillation of <48 h duration were randomly allocated to one of four groups: digitalis 0.75-1 mg i.v. plus quinidine 1100 mg (D+Q, 70 patients); propafenone 450-600 mg orally (PNF, 66 patients); propafenone 450-600 mg orally plus digitalis 0.750-1 mg i.v. (PNF+D, 70 patients); placebo (Pl, 40 patients). All patients underwent 24-h ECG Holter monitoring. Safety was assessed by evaluating the appearance of adverse events classified as mild, moderate and severe. No severe adverse events were reported. Short lasting asymptomatic atrial flutter episodes with atrio-ventricular conduction > or =2:1 were observed in 14% of the D+Q group, 21% PNF, 18% PNF+D and in 8% Pl. One patient in the D+Q group and four in the PNF+D group showed asymptomatic runs of 3-4 ventricular ectopic beats. Reversible sinus atrial blocks (<3 s) were detected in two patients of the D+Q group and in two of the PNF group. In patients with persistent atrial fibrillation the ventricular rate was similar in the four study groups. At 3 h the high efficacy of propafenone was confirmed. At the 24th hour no differences were found between active treatment and placebo arms.

CONCLUSION

Propafenone in a single oral loading dose is safe and promptly effective in patients with recent onset atrial fibrillation.

Randomized, crossover, controlled comparison of oral loading versus intravenous infusion of propafenone in recent-onset atrial fibrillation

A population of 123 patients with recent-onset (< 72 hours) atrial fibrillation (AF) without heart failure was randomly treated with propafenone (PFN) intravenously (i.v.) (2 mg/kg bolus followed by 0.0078 mg/kg/min infusion) or in a single oral dose (o.s.) (600 mg), or with placebo (PLA) (phase 1). If AF persisted 8 hours later, patients on active drugs received the alternative formulation (crossover), and patients receiving PLA remained on PLA (phase 2). A 24-hour Holter monitoring was performed and conversion to sinus rhythm (SR) at 1, 4, and 8 hours of each phase was used as the criterion of efficacy. Conversion to SR occurred within 1 hour in 48% of patients with i.v.-PFN, 15% with o.s.-PFN, and in 17% with PLA (both P < 0.05 vs i.v.-PFN). Oral PFN was superior to PLA at 4 hours (71% vs 33%, P = 0.001) and 8 hours (78% vs 48%, P < 0.01), and 1 at 8 hours also superior to i.v.-PFN (53%, P < 0.03). The mean conversion time within 4 hours was shorter with i.v.-PFN (25 +/- 15') than with o.s.-PFN (167 +/- 166', P < 0.001) or with PLA (156 +/- 107', P < 0.001). The rates of conversion to SR with i.v.-PFN after o.s.-PFN failure were comparable to PLA at any observation time, whereas nonresponders to i.v.-PFN who received o.s.-PFN had significantly higher conversion rates than with placebo at both 4 hours (65% vs 19%) and 8 hours (76% vs 24%; both P < 0.045). Neither serious adverse effects nor episodes of regular tachycardia with 1:1 AV conduction were noted. PFN administered intravenously or in a single oral loading dose was safe and efficacious in converting recent-onset AF to SR. The rates of conversion were different with different routes of administration: i.v.-PFN was superior to o.s.-PFN over a short observation period, while the overall efficacy of o.s.-PFN was superior at 8 hours.

Cardiac effects of quinidine on guinea-pig isolated perfused hearts after in vivo quinidine pretreatment

1 Experimental and clinical studies suggest that class I and class III antiarrhythmic drugs may be subject to pharmacological tolerance during long term treatment, leading to loss of therapeutic effectiveness. 2 The aim of this study was to ascertain whether prolonged in vivo treatment with the Class Ia agent quinidine can modify cardiac (electrical and mechanical) responses to the drug. 3 A group of guinea-pigs (n = 7) was treated intraperitoneally (q.d.) for 6 days with 75 mg kg-1 quinidine sulphate. Preliminary pharmacokinetic experiments indicated that this dose could attain Plasma concentrations similar to those that are therapeutic in man (2-5 mg l-1). A control group (n = 7) received a saline solution for the same period. 4 Twenty-four hours after the last administration hearts were removed and retrogradely perfused at constant flow (stimulation frequency: 2.5 Hz). The following parameters were measured: maximal derivative of intraventricular pressure (dP/dtmax); coronary perfusion pressure (Cp); PR, QRS and JT intervals, on surface ECG. The effects of quinidine on these parameters were measured at different concentrations (2, 4, 8, 12, 16, 20 microns) and compared in the two experimental groups. 5 In the group quinidine decreased in a dose-dependent manner dP/dt and increased PR and QRS intervals. JT interval was increased at the lowest concentrations and decreased at the highest (biphasic effect). Cp did not change significantly. 6 In the pretreated group quinidine qualitatively produced the same effects on dP/dt and ECG intervals as in control group. Also the magnitude of these effects was not significantly different between the two groups. In contrast with findings in control experiments. Cp was significantly decreased by increasing quinidine concentration. Mean baseline Cp was higher in pretreated than in the control group (though not significantly, P = 0.072) and quinidine addition abolished this difference. Thus, it is suggested that quinidine withdrawal induced a rebound increase in coronary tone, due to the unmasking of vasoconstrictor homeostatic mechanisms elicited by the in vivo vasodilating effect of the drug. 7 In conclusion, our data do not support the possibility that tolerance ensues during long term quinidine treatment, at least as far as electrophysiological and contractility effects are concerned. Further experimental work is needed to explain the appearance of a coronary vasodilating effect in pretreated hearts.

Conversion of recent onset atrial fibrillation to sinus rhythm using a single oral loading dose of propafenone: comparison of two regimens

A population of 105 patients with recent onset (< 72 h) atrial fibrillation was randomly treated with propafenone as a single oral loading dose of 450 mg (Regimen A) or 600 mg (Regimen B) or with placebo. A 24-h Holter was performed. Criteria of efficacy were conversion to sinus rhythm at 2, 4 and 8 h compared to placebo and also significant reduction of mean ventricular rate in persistent atrial fibrillation. After 2 h, regimen B was more effective than either regimen A (43% vs. 8%; p = 0.001) or placebo (11%; p = 0.004). At 4 h, both the active treatments were more effective than placebo (17% vs. 46% regimen A and 57% vs. regimen B; p < 0.04 and p < 0.001, respectively). Sinus rhythm resumed within 24 h in 71%, 80% and 69% of the patients with regimen A, B and placebo, respectively (p = not significant). The mean ventricular rate reduction after 1 h was 8%, 11% and 4% for regimen A, B and placebo, respectively (p < 0.005 vs. regimen B), and 17%, 25% and 6% respectively (p < 0.001 placebo vs. regimen A and B, p < 0.05 regimen B vs. A) at 2 h. No major adverse effect occurred. Atrial flutter with 1:1 atrioventricular conduction only in one case who received placebo. Propafenone acute oral administration is more effective than placebo in rapidly converting recent-onset atrial fibrillation to sinus rhythm and may be the treatment of choice in this setting limiting hospitalization and contributing to improved quality of life.

Propafenone for conversion of recent-onset atrial fibrillation. A controlled comparison between oral loading dose and intravenous administration

STUDY OBJECTIVE

To compare placebo vs two different regimens of propafenone administration--intravenous administration or short-term oral loading--in converting recent-onset atrial fibrillation to sinus rhythm.

DESIGN

Single-blind placebo-controlled study.

PATIENTS

Eighty-seven patients with atrial fibrillation of recent onset (< or = 7 days' duration) admitted to the hospital without signs of organic heart disease (n = 42) or with systemic hypertension without signs or symptoms of heart failure (n = 45). The patients were assigned randomly to treatment with intravenous propafenone (29 patients), oral propafenone (29 patients), or placebo (29 patients).

INTERVENTIONS

Administration of propafenone intravenously (2-mg/kg bolus followed by 0.0078 mg/kg/min) or as short-term oral loading (600 mg orally single dose). Patients were submitted to Holter monitoring and conversion to sinus rhythm was evaluated at 1, 3, and 8 h.

RESULTS

Conversion to sinus rhythm was obtained within 1 h in 28% with intravenous propafenone, in 3% with oral propafenone, and in 3% with placebo. At 3 h, the efficacy of intravenous propafenone (41%) and of oral propafenone (55%) were statistically superior to placebo (10% of conversions) and at 8 h either intravenous or oral propafenone were effective in almost two thirds of the patients with a statistical difference vs placebo, whose efficacy was 24%. No major side effects were observed.

CONCLUSIONS

Propafenone as an oral loading dose is an efficacious and fast way of treating atrial fibrillation of recent onset and due to its simplicity of administration and safety can be preferred to the intravenous route.

A controlled study on oral propafenone versus digoxin plus quinidine in converting recent onset atrial fibrillation to sinus rhythm

Eighty-seven patients with recent onset atrial fibrillation (< or = 8 days) without clinical signs of heart failure were randomly allocated to one of the following treatments: (i) oral propafenone (600 mg as a loading dose followed after 8 h by 300 mg t.i.d.); (ii) intravenous digoxin as acute scheme (up to 1.125 mg/24 h) followed after 6 h by hydroquinidine chlorhydrate (total dose, 1350 mg); or (iii) placebo. The patients were submitted to Holter monitoring for 48 h.

RESULTS

propafenone achieved higher successful conversion rates at 6, 12 and 24 h compared either with placebo (62% vs. 17%, 83% vs. 34%; 86% vs. 55%; P < 0.01, respectively) or with digoxin at 6 h (62% vs. 38%; P < 0.05) and digoxin plus quinidine at 12 h (83% vs. 48%; P < 0.05). At 48 h, a placebo conversion rate of 76% was observed with consequent lack of any significant difference with the active treatments. Mean conversion times within 48 h were 267 +/- 238 min for propafenone, 648 +/- 631 min for digoxin plus quinidine (P < 0.01 vs. propafenone) and 893 +/- 622 min for placebo (P < 0.001 vs. propafenone). Propafenone and digoxin plasma levels were within the therapeutic range. Asymptomatic phases of atrial flutter with > or = 2:1 atrio-ventricular conduction ratio were observed during Holter monitoring, before conversion to sinus rhythm, in four patients treated with propafenone, in one patient taking digoxin plus quinidine and in four patients with placebo.(ABSTRACT TRUNCATED AT 250 WORDS)