Propafenone. A reappraisal of its pharmacology, pharmacokinetics and therapeutic use in cardiac arrhythmias

Advancements in the diagnosis and management of premature ventricular contractions in pediatric patients

Background

Premature ventricular contractions (PVCs) are relatively common arrhythmias in the pediatric population, with implications that range from benign to potentially life-threatening. The management of PVCs in children poses unique challenges, and recent advancements in diagnostic and therapeutic options call for a comprehensive review of current practices.

Methods

This review synthesizes the latest literature on pediatric PVCs, focusing on publications from the past decade. We evaluate studies addressing the epidemiology, pathophysiology, diagnosis, and treatment of PVCs in children, including pharmacological, non-pharmacological, and invasive strategies.

Results

The review identifies key advancements in the non-invasive detection of PVCs, the growing understanding of their genetic underpinnings, and the evolving landscape of management options. We discuss the clinical decision-making process, considering the variable significance of PVCs in different pediatric patient subgroups, and highlight the importance of individualized care. Current guidelines and consensus statements are examined, and areas of controversy or limited evidence are identified.

Conclusions

Our review underscores the need for a nuanced approach to PVCs in children, integrating the latest diagnostic techniques with a tailored therapeutic strategy. We call for further research into long-term outcomes and the development of risk stratification tools to guide treatment. The potential of emerging technologies and the importance of multidisciplinary care are also emphasized to improve prognoses for pediatric patients with PVCs.

Catecholaminergic Polymorphic Ventricular Tachycardia: A Review of Therapeutic Strategies

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia syndrome characterized by bidirectional or polymorphic ventricular arrhythmia provoked by exercise or emotion. Most cases are caused by pathogenic variants in the gene encoding the cardiac ryanodine receptor (RYR2). The options for treating patients with CPVT have increased during the years, and evidence suggests that these have led to lower arrhythmic event rates. In addition, numerous potential new therapies are being investigated. In this review, we summarize the state of knowledge on both established and potential future treatment strategies for patients with CPVT and describe our approach to their management.

Chronic Propafenone Application Increases Functional KIR2.1 Expression In Vitro

Expression and activity of inwardly rectifying potassium (K_IR) channels within the heart are strictly regulated. K_IR channels have an important role in shaping cardiac action potentials, having a limited conductance at depolarized potentials but contributing to the final stage of repolarization and resting membrane stability. Impaired K_IR2.1 function causes Andersen-Tawil Syndrome (ATS) and is associated with heart failure. Restoring K_IR2.1 function by agonists of K_IR2.1 (AgoKirs) would be beneficial. The class 1c antiarrhythmic drug propafenone is identified as an AgoKir; however, its long-term effects on K_IR2.1 protein expression, subcellular localization, and function are unknown. Propafenone's long-term effect on K_IR2.1 expression and its underlying mechanisms in vitro were investigated. K_IR2.1-carried currents were measured by single-cell patch-clamp electrophysiology. K_IR2.1 protein expression levels were determined by Western blot analysis, whereas conventional immunofluorescence and advanced live-imaging microscopy were used to assess the subcellular localization of K_IR2.1 proteins. Acute propafenone treatment at low concentrations supports the ability of propafenone to function as an AgoKir without disturbing K_IR2.1 protein handling. Chronic propafenone treatment (at 25-100 times higher concentrations than in the acute treatment) increases K_IR2.1 protein expression and K_IR2.1 current densities in vitro, which are potentially associated with pre-lysosomal trafficking inhibition.

The many NOs to the use of Class IC antiarrhythmics: weren’t the guidelines too strict?

Class IC antiarrhythmic drugs (AADs) currently represent a cornerstone in the therapy of atrial fibrillation, both for the restoration of sinus rhythm and for the prophylaxis of long-term relapses. They also play an important role in the treatment of idiopathic ventricular arrhythmias. Following the results of the Cardiac Arrhythmia Suppression Trial study, flecainide and by extension the other Class IC AADs were contraindicated in patients with ischaemic and structural heart disease, due to their pro-arrhythmic effect and the consequent increase in mortality observed in the study. Recent studies carried out on patients with chronic coronary heart disease without previous heart attacks and/or residual ischaemia have shown a good safety profile for this class of drugs. In addition, other studies have shown excellent efficacy in the absence of pro-arrhythmic effects of Class IC AADs in patients with structural heart disease such as arrhythmogenic right ventricular cardiomyopathy (ARVC) and tachy-cardiomyopathy. The purpose of this review is to evaluate the appropriate use of Class IC AADs in the different patient subgroups, in the light of the evidence and new diagnostic and therapeutic tools available.

Cardioversion of recent-onset atrial fibrillation using intravenous antiarrhythmics: A European perspective

Pharmacological cardioversion using intravenous antiarrhythmic agents is commonly indicated in symptomatic patients with recent-onset atrial fibrillation (AF). Except in hemodynamically unstable patients who require emergency direct current electrical cardioversion, for the majority of hemodynamically stable patients, pharmacological cardioversion represents a valid option and requires the clinician to be familiar with the properties and use of antiarrhythmic agents. The main characteristics of selected intravenous antiarrhythmic agents for conversion of recent-onset AF, the reported success rates, and possible adverse events are discussed. Among intravenous antiarrhythmics, flecainide, propafenone, amiodarone, sotalol, dofetilide, ibutilide, and vernakalant are commonly used. Antazoline, an old antihistaminic agent with antiarrhythmic properties was also reported to give encouraging results in Poland. Intravenous flecainide and propafenone are the only Class I agents still recommended by recent guidelines. Intravenous new Class III agents as dofetilide and ibutilide have high and rapid efficacy in converting AF to sinus rhythm but require strict surveillance with electrocardiogram (ECG) monitoring during and after intravenous administration because of the potential risk of QT prolongation and Torsades de Pointes, which can be prevented and properly managed. Vernakalant, a partial atrial selective was shown to have a high success rate and to be safe in real-life use.

Propafenone Poisoning of a Female Adolescent After a Suicide Attempt

Propafenone is an antiarrhythmic agent for the management of ventricular and supraventricular tachycardia and atrial fibrillation. Propafenone poisoning is rare but may be life-threatening due to drug-induced arrhythmias. Electrocardiographic changes in PR, QRS, and QT intervals have been recorded. We present a case of a 15-year-old female adolescent who developed arrhythmias and convulsions due to propafenone intoxication, in an attempt to commit suicide. The outcome of the case was a full recovery from the arrhythmias and the seizures. The aim of this article is to highlight the possibility of a lethal intoxication by a common antiarrhythmic drug. Our case aims to present our therapeutic strategy that relies mainly on close monitoring of patients and cardiac output support.

Effect of CYP2D6 genetic polymorphism on peak propafenone concentration: no significant effect of CYP2D6*10

Aim: The study aims to investigate the clinical implication of nonfunctional poor metabolizer (PM) alleles and intermediate metabolizer (IM) alleles of CYP2D6, including the CYP2D6*10 allele which shows substrate-dependent decrease in enzymatic activity, in antiarrhythmic therapy using propafenone. Materials & methods: We examined serum propafenone concentrations and metabolic ratio, which was expressed as serum concentrations of propafenone to 5-hydroxypropafenone, in 66 Japanese patients with tachyarrhythmias. Results: The peak propafenone concentration and metabolic ratio in CYP2D6 PM allele carriers were higher than those in extensive metabolizer (EM)/EM, EM/IM and IM/IM genotype groups. Conclusion: Results suggest that CYP2D6 PM alleles affect peak propafenone concentration, but the CYP2D6 IM allele CYP2D6*10 has no clinical implication in propafenone dosing.

Chemoselective Hydrosilylation of the α,β-Site Double Bond in α,β- and α,β,γ,δ-Unsaturated Ketones Catalyzed by Macrosteric Borane Promoted by Hexafluoro-2-propanol

The B(C₆F₅)₃-catalyzed chemoselective hydrosilylation of α,β- and α,β,γ,δ-unsaturated ketones into the corresponding non-symmetric ketones in mild reaction conditions is developed. Nearly 55 substrates including those bearing reducible functional groups such as alkynyl, alkenyl, cyano, and aromatic heterocycles are chemoselectively hydrosilylated in good to excellent yields. Isotope-labeling studies revealed that hexafluoro-2-propanol also served as a hydrogen source in the process.

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.

Identification of 53 compounds that block Ebola virus-like particle entry via a repurposing screen of approved drugs

In light of the current outbreak of Ebola virus disease, there is an urgent need to develop effective therapeutics to treat Ebola infection, and drug repurposing screening is a potentially rapid approach for identifying such therapeutics. We developed a biosafety level 2 (BSL-2) 1536-well plate assay to screen for entry inhibitors of Ebola virus-like particles (VLPs) containing the glycoprotein (GP) and the matrix VP40 protein fused to a beta-lactamase reporter protein and applied this assay for a rapid drug repurposing screen of Food and Drug Administration (FDA)-approved drugs. We report here the identification of 53 drugs with activity of blocking Ebola VLP entry into cells. These 53 active compounds can be divided into categories including microtubule inhibitors, estrogen receptor modulators, antihistamines, antipsychotics, pump/channel antagonists, and anticancer/antibiotics. Several of these compounds, including microtubule inhibitors and estrogen receptor modulators, had previously been reported to be active in BSL-4 infectious Ebola virus replication assays and in animal model studies. Our assay represents a robust, effective and rapid high-throughput screen for the identification of lead compounds in drug development for the treatment of Ebola virus infection.

Structural basis of drugs that increase cardiac inward rectifier Kir2.1 currents

AIMS

We hypothesize that some drugs, besides flecainide, increase the inward rectifier current (IK1) generated by Kir2.1 homotetramers (IKir2.1) and thus, exhibit pro- and/or antiarrhythmic effects particularly at the ventricular level. To test this hypothesis, we analysed the effects of propafenone, atenolol, dronedarone, and timolol on Kir2.x channels.

METHODS AND RESULTS

Currents were recorded with the patch-clamp technique using whole-cell, inside-out, and cell-attached configurations. Propafenone (0.1 nM-1 µM) did not modify either IK1 recorded in human right atrial myocytes or the current generated by homo- or heterotetramers of Kir2.2 and 2.3 channels recorded in transiently transfected Chinese hamster ovary cells. On the other hand, propafenone increased IKir2.1 (EC50 = 12.0 ± 3.0 nM) as a consequence of its interaction with Cys311, an effect which decreased inward rectification of the current. Propafenone significantly increased mean open time and opening frequency at all the voltages tested, resulting in a significant increase of the mean open probability of the channel. Timolol, which interacted with Cys311, was also able to increase IKir2.1. On the contrary, neither atenolol nor dronedarone modified IKir2.1. Molecular modelling of the Kir2.1-drugs interaction allowed identification of the pharmacophore of drugs that increase IKir2.1.

CONCLUSIONS

Kir2.1 channels exhibit a binding site determined by Cys311 that is responsible for drug-induced IKir2.1 increase. Drug binding decreases channel affinity for polyamines and current rectification, and can be a mechanism of drug-induced pro- and antiarrhythmic effects not considered until now.

Successful treatment of suicide attempt by megadose of propafenone and captopril

Intoxication caused by propafenone is very rare, and there is no case reported before propafenone and captopril intoxication together. There are few case reports in the literature about intoxication with more than 6 g of propafenone. We present the clinical manifestation and successfully treatment of 9 g of propafenone and 1 g captopril intoxication in an 18-year-old female. An 18-year-old female was brought to the emergency department approximately half an hour after she committed suicide with 30 propafenone tablets, 300 mg each, and 20 captopril tablets, 50 mg each. Her fist electrocardiography (ECG) shows a chaotic ventricular rhythm with a prolonged QRS complex. After fluid and sodium bicarbonate infusion and permanent pacemaker implantation, sinus rhythm was achieved. This case, to our knowledge, is the first in that it describes the successful recovery of a patient who ingested extensively large doses of propafenone (9 g) and captopril (1 g), both of which are known to have severe cardiac side effects.

Wide complex tachycardia in the presence of class I antiarrhythmic agents: a diagnostic challenge

We present two patients with paroxysmal atrial fibrillation on class 1C antiarrhythmic drugs without concomitant atrioventricular (AV) nodal blocking agents who developed atrial flutter with 1:1 AV conduction. Their electrocardiogram revealed wide complex tachycardia with rates >200/minute. Atrial flutter with 1:1 conduction in the presence of class IC antiarrhythmic drugs may present a diagnostic challenge. These cases illustrate the importance of coadministering an AV nodal blocking agent with class IC antiarrhythmic agents in patients with atrial fibrillation. The differential diagnosis of wide complex tachycardia in patients taking class IC agents should include atrial flutter with 1:1 AV conduction.

Propafenone blocks human cardiac Kir2.x channels by decreasing the negative electrostatic charge in the cytoplasmic pore

Human cardiac inward rectifier current (IK1) is generated by Kir2.x channels. Inhibition of IK1 could offer a useful antiarrhythmic strategy against fibrillatory arrhythmias. Therefore, elucidation of Kir2.x channels pharmacology, which still remains elusive, is mandatory. We characterized the electrophysiological and molecular basis of the inhibition produced by the antiarrhythmic propafenone of the current generated by Kir2.x channels (IKir2.x) and the IK1 recorded in human atrial myocytes. Wild type and mutated human Kir2.x channels were transiently transfected in CHO and HEK-293 cells. Macroscopic and single-channel currents were recorded using the patch-clamp technique. At concentrations >1μM propafenone inhibited IKir2.x the order of potency being Kir2.3∼IK1>Kir2.2>Kir2.1 channels. Blockade was irrespective of the extracellular K(+) concentration whereas markedly increased when the intracellular K(+) concentration was decreased. Propafenone decreased inward rectification since at potentials positive to the K(+) equilibrium potential propafenone-induced block decreased in a voltage-dependent manner. Importantly, propafenone favored the occurrence of subconductance levels in Kir2.x channels and decreased phosphatidylinositol 4,5-bisphosphate (PIP2)-channel affinity. Blind docking and site-directed mutagenesis experiments demonstrated that propafenone bound Kir2.x channels at the cytoplasmic domain, close to, but not in the pore itself, the binding site involving two conserved Arg residues (residues 228 and 260 in Kir2.1). Our results suggested that propafenone incorporated into the cytoplasmic domain of the channel in such a way that it decreased the net negative charge sensed by K(+) ions and polyamines which, in turn, promotes the appearance of subconductance levels and the decrease of PIP2 affinity of the channels.

The corrected traditional equations for calculation of hepatic clearance that account for the difference in drug ionization in extracellular and intracellular tissue water and the corresponding corrected PBPK equation

The estimation of hepatic clearance, Clh, using in vitro data on metabolic stability of compound, its protein binding and blood–plasma equilibrium concentration ratio is commonly performed using well-stirred, parallel tube or dispersion models. It appears that for ionizable drugs there is a difference of the steady-state concentrations in extracelluar and intracellular water (at hepatocytes), where metabolism takes place. This occurs due to the different pH of extra- and intracellular water (7.4 and 7.0, respectively). The account of this fact leads to the novel equations for Clh . These equations include the additional parameter named ionization factor, FI, which is the ratio of the unionized drug fractions in plasma and intracellular tissue water (or the ratio of the unbound drug concentrations in intracellular tissue water and plasma at equilibrium). For neutral drugs FI = 1 and the novel equations coincide with the traditional ones. It is shown that the account of this factor may yield the calculated Clh up to 6.3-fold greater than that obtained by the traditional equations for the strong diprotic basic compounds, and up to 6.3-fold smaller for the strong diprotic acidic compounds. For triprotic acids and bases the difference could be as much as 15-fold. The account of pH difference between extra- and intracellular water also results in the change of the term commonly used to describe drug metabolic elimination rate in physiologically based pharmacokinetic (PBPK) equation. This consequently may lead to a noticeable change of drug concentration-time profiles in plasma and tissues. The effect of ionization factor is especially pronounced for the low-extraction ratio drugs. The examples of significant improvement in the prediction of hepatic clearance due to the account of ionization factor are provided. A more general equation for hepatic clearance, which accounts for ionization factor and possible drug uptake and efflux, is obtained.

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.

Acute management of atrial fibrillation and atrial flutter in the critical care unit: should it be ibutilide?

BACKGROUND

Ibutilide is currently indicated for the rapid conversion of atrial fibrillation (Afb) or atrial flutter (Afl) of recent onset but limited to patients who are hemodynamically stable and without symptomatic cardiovascular conditions.

HYPOTHESIS

The study was undertaken to assess the efficacy and safety of ibutilide in patients with Afb or Afl associated with acute cardiovascular-medical disorders and in patients receiving prior selective antiarrhythmic drug therapy.

METHODS

The study included 34 patients, mean age 75 +/- 16.3 years, with Afb (n = 25) or Afl (n = 9) having a variety of disorders, for example, congestive heart failure, unstable angina, borderline hypotension, respiratory failure, and chronic renal failure. Prior antiarrhythmic drugs consisted of propafenone (n = 5) or amiodarone (n = 3). Eligibility for cardioversion was established with appropriate anticoagulation or transesophageal echocardiography findings. Ibutilide was given as up to two 10 min infusions of 1 mg separated by 10 min.

RESULTS

The overall conversion rate after ibutilide was 79.4% (27/34 patients): 80% for Afb and 78% for Afl. More than 90% converted within 1 h of treatment. A high conversion rate of 92% resulted in those with an arrhythmia duration of < or = 1 week. All eight patients with prior antiarrhythmic therapy converted to sinus rhythm. The average baseline QTc interval for all patients increased 17.1% (397 +/- 63.3 to 465 +/- 60.2 ms) at 30 min. For eight patients (including four who received prior antiarrhythmic drugs), QTc interval prolongation > or = 500 ms was associated with nearly half the entire incidence of arrhythmic events. Proarrhythmia, the exclusive adverse effect, consisted of ventricular extrasystoles (n = 10) and nonsustained monomorphic ventricular tachycardia (VT) (n = 2) managed with intravenous MgSO4, and sustained polymorphic VT (n = 1) requiring electrical cardioversion.

CONCLUSION

Ibutilide is an effective and well tolerated drug for the rapid termination of Afb or Afl of recent onset associated with symptomatic and/or hemodynamically unstable disorders, and it is most efficacious (> or = 90%) when the atrial arrhythmia is < or = 1 week in duration. Proarrhythmic events are readily manageable in a monitored unit with access to appropriate treatment.

Propafenone-induced drug fever in the absence of agranulocytosis

Propafenone is an antiarrhythmic drug used in the treatment of life-threatening ventricular tachyarrhythmias. Adverse reactions necessitating discontinuation of the medication are common. Propafenone-induced drug fever has not been definitively proven. We present a case report of drug fever secondary to propafenone, confirmed with rechallenge.

Inhibitory Effects of Propafenone on the Pharmacokinetics of Caffeine in Humans

CYP1A2 is involved in the metabolism of both caffeine and propafenone, a class Ic antiarrhythmic agent. Despite the widespread consumption of caffeine, drug-drug interactions with this agent are often overlooked. This study investigated effects of propafenone on the pharmacokinetics of caffeine. Eight healthy volunteers were included in our study. A total of 300 mg of caffeine was given on 2 occasions, once alone and once during the coadministration of 300 mg propafenone. Serial blood samples were collected and pharmacokinetic parameters were estimated using a population pharmacokinetic approach. A one-compartment PK model with first-order absorption and elimination described plasma concentration profiles. Concomitant administration of propafenone decreased caffeine oral clearance from 8.3 +/- 0.9 L/h to 5.4 +/- 0.7 L/h (P < 0.05). Elimination half-life of caffeine was also increased 54% by propafenone. One of our volunteers was a poor metabolizer of CYP2D6. Concomitant administration of propafenone to this volunteer caused the greatest increase in caffeine plasma concentrations. These results support the concept of competitive inhibition between propafenone and caffeine. Our results suggest that propafenone causes significant inhibition of CYP1A2 activity leading to a decrease in the clearance of caffeine. Caffeine has intrinsic proarrhythmic effects; thus, its coadministration with an antiarrhythmic agent such as propafenone should be used with caution, especially in patients with poor CYP2D6 activity.

Characterisation of (R/S)-propafenone and its metabolites as substrates and inhibitors of P-glycoprotein

Digoxin is a drug with a narrow therapeutic index, which is a substrate of the ATP-dependent efflux pump P-glycoprotein. Increased or decreased digoxin plasma concentrations occur in humans due to the inhibition or induction of this drug transporter in organs with excretory function such as small intestine, liver and kidney. It is well known that serum concentrations of digoxin increase considerably in humans if propafenone is given simultaneously. However, it has not been investigated in detail whether propafenone and its metabolites are substrates and/or inhibitors of human P-glycoprotein. The aim of this study, therefore, was to investigate the P-glycoprotein-mediated transport and inhibition properties of propafenone and its major metabolites 5-hydroxypropafenone and N-desalkylpropafenone in Caco-2 cell monolayers. Inhibition of P-glycoprotein-mediated transport by propafenone and its metabolites was determined using digoxin as a P-glycoprotein substrate. No polarised transport was observed for propafenone and N-desalkylpropafenone in Caco-2 cell monolayers. However, 5-hydroxypropafenone translocation was significantly greater from basal-to-apical compared with apical-to-basal (P(app) basal-apical vs. P(app) apical-basal, 10.21+/-2.63 x 10(-6) vs. 4.34+/-1.84 x 10(-6) cm/s; P<0.01). Moreover, propafenone, 5-hydroxypropafenone and N-desalkylpropafenone inhibited P-glycoprotein-mediated digoxin transport with IC(50) values of 6.8, 19.9, and 21.3 microM, respectively. In summary, whereas propafenone and N-desalkylpropafenone are not substrates of P-glycoprotein, 5-hydroxypropafenone is translocated by human P-glycoprotein across cell monolayers. In addition, propafenone and its two major metabolites 5-hydroxypropafenone and N-desalkylpropafenone are inhibitors of human P-glycoprotein and therefore contribute to the digoxin-propafenone interaction observed in humans.

Ontogeny of hepatic and renal systemic clearance pathways in infants: part II

Maturation of drug systemic clearance mechanisms during the postnatal period produces dramatic and rapid changes in an infant's capacity to eliminate drugs. A tentative general mathematical model describing the ontogeny of hepatic cytochrome P450 (CYP) enzyme-mediated clearance and renal clearance due to glomerular filtration in the first 6 months of life was elaborated from age-specific in vitro hepatic microsomal activity data (normalised to amount of hepatic microsomal protein) for enzyme-specific probe substrates and in vivo probe substrate data for glomerular filtration (normalised to bodyweight), respectively. The model predicts an age- and clearance pathway-specific Infant Scaling Factor (ISF) for the first 6 months of life. The ISF reflects functional maturation of a specific clearance pathway (normalised to bodyweight) relative to adult values. Therefore, the ISF directly correlates adult clearance values with an infant's capacity to eliminate drugs. Substitution of appropriate model parameter estimates and the age of the infant into the model provides an estimated ISF value, which may then be used to predict the contribution of a particular clearance pathway to total systemic clearance in the infant when adult systemic clearance values are known. The model was tested for its ability to predict infant systemic clearance of drugs whose elimination is principally mediated by a single CYP enzyme or by glomerular filtration. The model performed reasonably well for CYP1A2 and CYP3A4, but poorer predictions were obtained for CYP2D6 and CYP2C because of lack of model complexity and/or inadequate hepatic microsomal activity data to fully describe the maturational process of functional enzyme. For renal clearance due to glomerular filtration, data normalised to bodyweight (kg) showed a limited maturational trend, suggesting that adult renal clearances normalised to bodyweight might reasonably predict infant renal clearances in the first 6 months of life. The model provided reasonable predictions of renal clearance due to glomerular filtration in the infant.

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.

Supraventricular tachycardia

Supraventricular tachycardias (SVT) comprise those tachycardias that originate above the bifurcation of the bundle of His. They can be classified broadly as AV node dependent and AV node independent. The mechanism and clinical manifestation of SVTs, which is essential to their correct diagnosis, is reviewed. The therapeutic management of SVTs, including acute and chronic drug therapy and catheter ablation, is discussed also.

Determination of propafenone and its phase I and phase II metabolites in plasma and urine by high-performance liquid chromatography-electrospray ionization mass spectrometry

A sensitive method was developed to determine propafenone, 5-hydroxypropafenone, N-despropylpropafenone and propafenone glucuronides in human plasma and urine by HPLC-electrospray ionization mass spectrometry with the respective deuterated analogues as internal standards. The analytes were extracted by a single solid-phase extraction, collecting two fractions, one containing the glucuronides and the other propafenone and the phase I metabolites 5-hydroxypropafenone and N-despropylpropafenone. The mobile phases used for HPLC were: (A) 5 mM ammonium acetate in water and (B) 5 mM ammonium acetate in methanol-tetrahydrofuran (50:50, v/v). Separation of the diastereoisomeric propafenone glucuronides was achieved on a Spherisorb ODS 2 column (150 x 2.0 mm I.D., particle size 5 microm) at a flow-rate of 0.3 ml/min using a linear gradient from 20% B to 50% B in 15 min. For separation of propafenone, 5-hydroxypropafenone and N-desalkylpropafenone a linear gradient from 50% B to 80% B in 10 min was employed. The mass spectrometer was operated in the selected ion monitoring mode using the respective MH+ ions for quantification. The limits of quantification achieved with this method were 10 pmol/ml for propafenone, 5-hydroxypropafenone, R- and S-propafenone glucuronide and 20 pmol/ml for N-desalkylpropafenone using 0.5 ml of plasma. Reproducibility and accuracy was below 12% for each analyte over the whole concentration range measured. The method was applied to a pharmacokinetic study assessing the influence of rifampicin on propafenone disposition.

Clinically significant pharmacokinetic interactions between dietary caffeine and medications

Caffeine from dietary sources (mainly coffee, tea and soft drinks) is the most frequently and widely consumed CNS stimulant in the world today. Because of its enormous popularity, the consumption of caffeine is generally thought to be safe and long term caffeine intake may be disregarded as a medical problem. However, it is clear that this compound has many of the features usually associated with a drug of abuse. Furthermore, physicians should be aware of the possible contribution of dietary caffeine to the presenting signs and symptoms of patients. The toxic effects of caffeine are extensions of their pharmacological effects. The most serious caffeine-related CNS effects include seizures and delirium. Other symptoms affecting the cardiovascular system range from moderate increases in heart rate to more severe cardiac arrhythmia. Although tolerance develops to many of the pharmacological effects of caffeine, tolerance may be overwhelmed by the nonlinear accumulation of caffeine when its metabolism becomes saturated. This might occur with high levels of consumption or as the result of a pharmacokinetic interaction between caffeine and over-the-counter or prescription medications. The polycyclic aromatic hydrocarbon-inducible cytochrome P450 (CYP) 1A2 participates in the metabolism of caffeine as well as of a number of clinically important drugs. A number of drugs, including certain selective serotonin reuptake inhibitors (particularly fluvoxamine), antiarrhythmics (mexiletine), antipsychotics (clozapine), psoralens, idrocilamide and phenylpropanolamine, bronchodilators (furafylline and theophylline) and quinolones (enoxacin), have been reported to be potent inhibitors of this isoenzyme. This has important clinical implications, since drugs that are metabolised by, or bind to, the same CYP enzyme have a high potential for pharmacokinetic interactions due to inhibition of drug metabolism. Thus, pharmacokinetic interactions at the CYP1A2 enzyme level may cause toxic effects during concomitant administration of caffeine and certain drugs used for cardiovascular, CNS (an excessive dietary intake of caffeine has also been observed in psychiatric patients), gastrointestinal, infectious, respiratory and skin disorders. Unless a lack of interaction has already been demonstrated for the potentially interacting drug, dietary caffeine intake should be considered when planning, or assessing response to, drug therapy. Some of the reported interactions of caffeine, irrespective of clinical relevance, might inadvertently cause athletes to exceed the urinary caffeine concentration limit set by sports authorities at 12 mg/L. Finally, caffeine is a useful and reliable probe drug for the assessment of CYP1A2 activity, which is of considerable interest for metabolic studies in human populations.

Effects of liver disease on pharmacokinetics. An update

Liver disease can modify the kinetics of drugs biotransformed by the liver. This review updates recent developments in this field, with particular emphasis on cytochrome P450 (CYP). CYP is a rapidly expanding area in clinical pharmacology. The information currently available on specific isoforms involved in drug metabolism has increased tremendously over the latest years, but knowledge remains incomplete. Studies on the effects of liver disease on specific isoenzymes of CYP have shown that some isoforms are more susceptible than others to liver disease. A detailed knowledge of the particular isoenzyme involved in the metabolism of a drug and the impact of liver disease on that enzyme can provide a rational basis for dosage adjustment in patients with hepatic impairment. The capacity of the liver to metabolise drugs depends on hepatic blood flow and liver enzyme activity, both of which can be affected by liver disease. In addition, liver failure can influence the binding of a drug to plasma proteins. These changes can occur alone or in combination; when they coexist their effect on drug kinetics is synergistic, not simply additive. The kinetics of drugs with a low hepatic extraction are sensitive to hepatic failure rather than to liver blood flow changes, but drugs having a significant first-pass effect are sensitive to alterations in hepatic blood flow. The drugs examined in this review are: cardiovascular agents (angiotensin converting enzyme inhibitors, angiotensin II receptor antagonists, calcium antagonists, ketanserin, antiarrhythmics and hypolipidaemics), diuretics (torasemide), psychoactive and anticonvulsant agents (benzodiazepines, flumazenil, antidepressants and tiagabine), antiemetics (metoclopramide and serotonin antagonists), antiulcers (acid pump inhibitors), anti-infectives and antiretroviral agents (grepafloxacin, ornidazole, pefloxacin, stavudine and zidovudine), immunosuppressants (cyclosporin and tacrolimus), naltrexone, tolcapone and toremifene. According to the available data, the kinetics of many drugs are altered by liver disease to an extent that requires dosage adjustment; the problem is to quantify the required changes. Obviously, this requires the evaluation of the degree of hepatic impairment. At present there is no satisfactory test that gives a quantitative measure of liver function and its impairment. A critical evaluation of these methods is provided. Guidelines providing a rational basis for dosage adjustment are illustrated. Finally, it is important to consider that liver disease not only affects pharmacokinetics but also pharmacodynamics. This review also examines drugs with altered pharmacodynamics.

Propafenone blocks ATP-sensitive K+ channels in rabbit atrial and ventricular cardiomyocytes

Propafenone, a class I antiarrhythmic agent, inhibits several membrane currents (I(Na), I(Ca), I(K), Ito), however, its effects on ATP-sensitive potassium current (I(K)ATP) of cardiac cells have not been tested. We evaluated the blocking effects of 0.1 to 100 microM propafenone applications at 35 degrees C on the whole-cell I(K)ATP as triggered by dinitrophenol (75 microM) in adult rabbit dissociated atrial and ventricular cardiomyocytes in comparison. The block of I(K)ATP by propafenone was dose-dependent, fully reversible and voltage-independent. The dose-response relation, as evaluated at 0 mV for atrial myocytes (ED50 = 1.26+/-0.17 microM, Hill number = 1.25+/-0.22) was significantly shifted to the left vs. that in ventricular myocytes (ED50 = 4.94+/-0.59 microM, Hill number = 1.22+/-0.14). It is concluded that propafenone blocks cardiac I(K)ATP at a single site with 4 times higher affinity for the drug in atrial myocytes. This block of cardiac I(K)ATP might play a role in the beneficial and adverse effects of the drug.

Effects of propafenone and 5-hydroxy-propafenone on hKv1.5 channels

1. The goal of this study was to analyse the effects of propafenone and its major metabolite, 5-hydroxy-propafenone, on a human cardiac K+ channel (hKv1.5) stably expressed in Ltk- cells and using the whole-cell configuration of the patch-clamp technique. 2. Propafenone and 5-hydroxy-propafenone inhibited in a concentration-dependent manner the hKv1.5 current with K(D) values of 4.4+/-0.3 microM and 9.2+/-1.6 microM, respectively. 3. Block induced by both drugs was voltage-dependent consistent with a value of electrical distance (referenced to the cytoplasmic side) of 0.17+/-0.55 (n=10) and 0.16+/-0.81 (n=16). 4. The apparent association (k) and dissociation (l) rate constants for propafenone were (8.9+/-0.9) x 10(6) M(-1) s(-1) and 39.5+/-4.2 s(-1), respectively. For 5-hydroxy-propafenone these values averaged (2.3+/-0.3) x 10(6) M(-1) s(-1) and 21.4+/-3.1 s(-1), respectively. 5. Both drugs reduced the tail current amplitude recorded at -40 mV after 250 ms depolarizing pulses to +60 mV, and slowed the deactivation time course resulting in a 'crossover' phenomenon when the tail currents recorded under control conditions and in the presence of each drug were superimposed. 6. Both compounds induced a small but statistically significant use-dependent block when trains of depolarizations at frequencies between 0.5 and 3 Hz were applied. 7. These results indicate that propafenone and its metabolite block hKv1.5 channels in a concentration-, voltage-, time- and use-dependent manner and the concentrations needed to observe these effects are in the therapeutical range.

Stereoselective steady state disposition and action of propafenone in Chinese subjects

AIMS

To investigate the steady state disposition and action of racemic propafenone and its enantiomers and the potential for an enantiomer-enantiomer interaction in Chinese subjects.

METHODS

Eight healthy male Chinese individuals received in a double-blind, randomized, cross-over study racemic propafenone (150 mg every 6 h), (S)-, and (R)-propafenone (150 mg each every 6 h) and placebo orally for 4 days. During the last dosing interval the plasma concentrations of both enantiomers of propafenone were measured and ECG, blood pressure (MAP) and heart rate were monitored.

RESULTS

Whereas the apparent elimination half-life (t1/2,z), mean residence time (MRT) and time to reach peak concentrations (tmax) of (S)- and (R)-propafenone were similar and independent of the administered agent, significant differences were observed in the apparent oral clearance (CLO) of the enantiomers. During dosing with racemic propafenone CLO of (S)- and (R)-propafenone averaged (+/-s.d.) 1226+751 and 1678+625 ml min(-1), respectively (P=0.024). Following the administration of the pure enantiomers CLO of (S)-propafenone increased (P= 0.007) to 2028+/-959 ml min(-1) and that of (R)-propafenone was reduced (P= 0.042) to 1318+/-867 ml min(-1). Both enantiomers and the racemate caused about a 10% increase in the QRS duration (P<0.05) and PR-interval (P<0.01) when compared with placebo. The increase in maximum exercise heart rate was significantly (P<0.05) attenuated only at 3 h following the administration of the racemate and the S-enantiomer. MAP and QTC were not affected significantly.

CONCLUSIONS

These data indicate that the stereoselective disposition of propafenone is similar in Chinese and Caucasian subjects (previously published findings), the (R)-enantiomer being cleared more rapidly. A similar enantiomer-enantiomer interaction also occurred. Thus, when the racemate was given, the elimination of (S)-propafenone was impaired and that of the (R)-form accelerated compared with single enantiomer administration. The results indicate that dosage adjustments are probably not required in Chinese patients receiving propafenone.

Placebo-controlled evaluations of propafenone for atrial tachyarrhythmias

This review summarizes the results of placebo-controlled trials of propafenone, a class IC antiarrhythmic drug, in patients with supraventricular tachycardia, atrial fibrillation (AF), and atrial flutter. Success rates for cardioversion from AF or flutter to sinus rhythm of 9-93% have been obtained with intravenous propafenone. The duration of arrhythmia is an important factor in the degree of success. The use of a single oral dose has also been reported to be effective in a number of studies. Several placebo-controlled studies have confirmed the effectiveness of propafenone in the long-term suppression of both suproventricular tachycardia and AF and flutter. These reported trials have shown consistent benefit with propafenone compared with placebo in preventing arrhythmia recurrence. The adverse side effect profile for propafenone has also been reviewed with particular reference to the potential for proarrhythmia. The rate of side effects is dose-dependent and tends to be higher in patients with underlying structural heart disease. Overall propafenone has been shown to be an effective antiarrhythmic drug with an acceptable side effect profile for the acute and long-term treatment of supraventricular arrhythmias.

Atrial flutter with 1:1 atrioventricular conduction caused by propafenone

We describe a case of 1:1 atrial flutter in a patient with coronary disease taking propafenone. In atrial flutter, the atrial rate is usually about 300 beats/min with 2:1 AV conduction and a ventricular rate of 150 beats/min. Class IA antiarrhythmic drugs, especially quinidine and disopyramide, may cause 1:1 AV response because they reduce atrial rate and are vagolytic. However, propafenone is a Class IC agent and has no anticholinergic properties, and the occurrence of 1:1 AV conduction at a rate of about 250 beats/min is an important side effect that, although uncommon, should be recognized.

Standards of laboratory practice: cardiac drug monitoring

In this Standard of Laboratory Practice we recommend guidelines for therapeutic monitoring of cardiac drugs. Cardiac drugs are primarily used for treatment of angina, arrhythmias, and congestive heart failure. Digoxin, used in congestive heart failure, is widely prescribed and therapeutically monitored. Monitoring and use of antiarrhythmics such as disopyramide and lidocaine have been steadily declining. Immunoassay techniques are currently the most popular methods for measuring cardiac drugs. Several reasons make measurement of cardiac drugs in serum important: their narrow therapeutic index, similarity in clinical complications and presentation of under- and overmedicated patients, need for dosage adjustments, and confirmation of patient compliance. Monitoring may also be necessary in other circumstances, such as assessment of acetylator phenotypes. We present recommendations for measuring digoxin, quinidine, procainamide (and N-acetylprocainamide), lidocaine, and flecainide. We discuss guidelines for measuring unbound digoxin in the presence of an antidote (Fab fragments), for characterizing the impact of digoxin-like immunoreactive factor (DLIF) and other cross-reactants on immunoassays, and for monitoring the unbound (free fraction) of drugs that bind to α1-acid glycoprotein. We also discuss logistic, clinical, hospital, and laboratory practice guidelines needed for implementation of a successful therapeutic drug monitoring service for cardiac drugs.

Rate-dependent effects of ajmaline and propafenone on atrioventricular conduction

The aim of the present study was to characterize the time dependence of the depressant effects of ajmaline and propafenone on the Ca(2+)-channel-dependent tissue of the atrioventricular node in isolated guinea pig hearts perfused by the method of Langendorff. Ajmaline at a concentration of 0.03 microM and propafenone at a concentration of 0.3 microM caused a significant and comparable prolongation of the His bundle and atrioventricular conduction time (AVCT). When the pacing cycle length was abruptly shortened from 240 to 180 ms, the mean time constant (tau on) of the rate-dependent AVCT prolongation was comparable for ajmaline and propafenone. In contrast, if the pacing cycle length was abruptly increased from 180 to 240 ms the mean time constant (tau off) for ajmaline was significantly higher than for propafenone. The rate-dependent increase of the atrioventricular effective refractory period was significantly more pronounced in the presence of ajmaline than of propafenone. Ajmaline and propafenone affect the Ca(2+)-channel-dependent tissue of the myocardium. The more pronounced rate-dependent effect of ajmaline on the atrioventricular effective refractory period may be explained by a slower dissociation kinetic from the channel.

Intravenous propafenone: efficacy and safety in the conversion to sinus rhythm of recent onset atrial fibrillation--a single-blind placebo-controlled study

The effectiveness of intravenous propafenone for conversion to sinus rhythm (SR) of paroxysmal atrial fibrillation (AF), lasting less than 7 days, was evaluated with a single-blind, randomized, placebo-controlled study, given the possible spontaneous conversion of this arrhythmia. Group 1 (98 patients) received intravenous propafenone (2 mg/kg iv over 10 minutes followed by 0.007 mg/kg/min); and group 2 (84 patients) received intravenous placebo (0.9% saline solution). The infusion was continued until restoration of SR but no longer than 24 hours. Eight-nine patients (90.8%) received propafenone and 27 patients (32%) receiving placebo were converted to SR (p < 0.005). The mean conversion time was 2.46 +/- 2.59 hours in group 1 and 17.15 +/- 5.78 hours in group 2 (p < 0.005). In patients treated with propafenone, conversion of SR mostly occurred in the first 4 hours (86.5%), considered to be the optimal infusion time in our experience. In both groups, the left atrial size was significantly larger in nonconverted than in converted patients. Similarly, the duration of the arrhythmia was significantly longer in nonconverted patients. In nonconverted patients, the mean ventricular rate decreased from 143 +/- 16 beats/min to 101 +/- 18 beats/ min after propafenone and from 135 +/- 19 beats/min to 119 +/- 16 beats/min after placebo (group 1 vs. group 2: p < 0.005). Two episodes of sinus standstill (3.4 and 3.8, seconds, respectively) occurred at SR restoration obtained with propafenone. Intravenous propafenone is an effective, safe, and usually rapid drug for AF treatment. Moreover, it produces a real and significant reduction in the mean ventricular rate in nonconverted patients.

Propafenone: an effective agent for the management of supraventricular arrhythmias

Propafenone is a sodium channel blocking antiarrhythmic drug. It also has beta-adrenergic, potassium channel, and weak calcium channel blocking activity. The drug is metabolized in the liver with rates dependent on the debrisoquin phenotype. The saturable metabolism results in nonlinear pharmacokinetics. The metabolites retain sodium channel blocking activity but little beta-adrenergic blocking activity. Both controlled and noncontrolled studies have documented its efficacy in a variety of supraventricular arrhythmias. Intravenous propafenone is effective in converting atrial fibrillation to normal sinus rhythm. Chronic oral administration decreases the frequency of recurrence of atrial fibrillation and paroxysmal supraventricular tachycardia. The drug is particularly effective in the Wolff-Parkinson-White syndrome. The drug may produce SA block in patients with underlying sinus node dysfunction. Propafenone has comparatively few noncardiac side effects. It is a useful primary drug or an alternative to more commonly used drugs used for the treatment of supraventricular arrhythmias.

Propafenone preferentially blocks the rapidly activating component of delayed rectifier K+ current in guinea pig ventricular myocytes. Voltage-independent and time-dependent block of the slowly activating component

The effects of propafenone on the delayed rectifier K+ current were studied in guinea pig ventricular myocytes by using the patch-clamp technique. In these myocytes, this current consists of at least two components: a La(3+)-sensitive component activating rapidly with moderate depolarizations and a La(3+)-resistant current slowly activating at more positive potentials. In the absence of La3+ (when both components are present), propafenone inhibited the delayed outward current, its effects being more marked after weak than after strong depolarizations. Propafenone-induced block of the tail currents elicited on return to -30 mV was more marked after short than after long depolarizing pulses. In the presence of 1 mumol/L propafenone, the envelope-of-tails test was satisfied, thus indicating that at this concentration propafenone completely blocks the rapidly activating component. In the presence of La3+ (when only the slow component is present), the steady state inhibition induced by 5 mumol/L propafenone on both the maximum activated and the tail currents was independent of the test pulse voltage. Development of propafenone-induced block on the slowly activating component was very fast and linked to channel opening. In addition, the blockade appeared to be use dependent, with the rate constant of the onset kinetics at 2 Hz being 0.44 +/- 0.1 pulse-1. The recovery process from propafenone-induced block exhibited a time constant of 2.5 +/- 0.4 s. These results indicated that propafenone preferentially inhibits the rapidly activating component of the delayed rectifier and that it blocks in a voltage-independent and time-dependent manner the slow component of this current.

An enantiomer-enantiomer interaction of (S)- and (R)-propafenone modifies the effect of racemic drug therapy

BACKGROUND

Therapy with racemic compounds produces effects that can be attributed to both (S)- and (R)-enantiomers. Here we have tested the hypothesis that an enantiomer-enantiomer interaction would modulate the effects of treatment with a racemate, the antiarrhythmic propafenone. Previous studies have shown that while the enantiomers of propafenone exert similar sodium channel-blocking (QRS widening) effects, it is the (S)-enantiomer that produces beta-blockade; moreover, we have demonstrated recently that (R)-propafenone inhibits the metabolism of (S)-propafenone in vitro.

METHODS AND RESULTS

This single-blind, randomized study compared the effects of (R/S)-, (S)-, (R)-propafenone (150 mg q 6 hours for 4 days) and placebo on QRS duration (delta QRS) and on maximum exercise heart rate (delta HRmax), an index of beta-blockade. The clearance of (S)-propafenone was significantly lower (-55 +/- 24%, P < .001) during treatment with (R/S)-propafenone than with the (S)-enantiomer alone, and delta HRmax was significantly altered during (R/S)-propafenone (-8.8 +/- 6.6 beats per minute; P < .01) and during (S)-propafenone (-4.3 +/- 4.8 beats per minute; P < .01) but not during (R)-propafenone (-1.8 +/- 6.4 beats per minute) or placebo (0.3 +/- 7.1 beats per minute). In contrast, (R/S)-, (S)-, and (R)-propafenone all prolonged QRS compared with placebo.

CONCLUSIONS

These data indicate that (R)-propafenone impairs the disposition of (S)-propafenone in humans. As a result, the beta-blocking effects of 150 mg of racemic propafenone (75 mg of the [S]-enantiomer) were more pronounced than those of 150 mg of (S)-propafenone alone. Thus, the effects of racemic drug therapy are not necessarily those predicted by summation of the effects of the individual enantiomers.