Propafenone Hydrochloride Tablets
TABLE OF CONTENTS
Propafenone hydrochloride is an antiarrhythmic drug with some structural similarities to beta-blocking agents. Chemically, propafenone HCl is 2'-[2-Hydroxy-3-(propylamino)-propoxy]-3-phenylpropiophenone hydrochloride with the following structural formula:
Molecular formula: C21H27NO3 • HCl - Molecular weight: 377.90
Propafenone hydrochloride occurs as colorless crystals or white crystalline powder with a very bitter taste. It is slightly soluble in water (20°C), chloroform and ethanol.
Propafenone hydrochloride is supplied in scored, film-coated tablets of 150, 225 and 300 mg for oral administration.
Inactive ingredients: carnauba wax, hypromellose, magnesium stearate, polydextrose, polyethylene glycol, polysorbate 80, povidone, pregelatinized starch (corn), propylene glycol, sodium starch glycolate, titanium dioxide, and triacetin.
|2. INDICATIONS AND USAGE|
Propafenone is indicated to:
• prolong the time to recurrence of paroxysmal atrial fibrillation/flutter (PAF) associated with disabling symptoms in patients without structural heart disease.
• prolong the time to recurrence of paroxysmal supraventricular tachycardia (PSVT) associated with disabling symptoms in patients without structural heart disease.
• treat documented ventricular arrhythmias, such as sustained ventricular tachycardia that, in the judgment of the physician, are life-threatening. Initiate treatment in the hospital.
• The use of propafenone in patients with permanent atrial fibrillation (AF) or in patients exclusively with atrial flutter or PSVT has not been evaluated. Do not use propafenone to control ventricular rate during AF.
• Some patients with atrial flutter treated with propafenone have developed 1:1 conduction, producing an increase in ventricular rate. Concomitant treatment with drugs that increase the functional atrioventricular (AV) nodal refractory period is recommended.
• The use of propafenone in patients with chronic atrial fibrillation has not been evaluated.
• Because of the proarrhythmic effects of propafenone, its use with lesser ventricular arrhythmias is not recommended, even if patients are symptomatic, and any use of the drug should be reserved for patients in whom, in the opinion of the physician, the potential benefits outweigh the risks.
• The effect of propafenone on mortality has not been determined [see Boxed Warning].
|3. DOSAGE AND ADMINISTRATION|
The dose of propafenone must be individually titrated on the basis of response and tolerance. Initiate therapy with propafenone 150 mg given every eight hours (450 mg/day). Dosage may be increased at a minimum of 3 to 4 day intervals to 225 mg every 8 hours (675 mg/day). If additional therapeutic effect is needed, the dose of propafenone may be increased to 300 mg every 8 hours (900 mg/day). The usefulness and safety of dosages exceeding 900 mg per day have not been established.
In patients with hepatic impairment or thosewith significant widening of the QRS complex or second or third degree AV block, consider reducing the dose.
As with other antiarrhythmic agents, in the elderly or in ventricular arrhythmia patients with marked previous myocardial damage, the dose of propafenone should be increased more gradually during the initial phase of treatment.
The combination of CYP3A4 inhibition and either CYP2D6 deficiency or CYP2D6 inhibition with the simultaneous administration of propafenone may significantly increase the concentration of propafenone and thereby increase the risk of proarrhythmia and other adverse events. Therefore, avoid simultaneous use of propafenone with both a CYP2D6 inhibitor and a CYP3A4 inhibitor [see Warnings and Precautions (7.4) and Drug Interactions (10.1)].
Propafenone HCl is contraindicated in the following circumstances:
• Heart failure
• Cardiogenic shock
• Sinoatrial, atrioventricular and intraventricular disorders of impulse generation or conduction (e.g., sick sinus node syndrome, AV block) in the absence of an artificial pacemaker
• Known Brugada Syndrome
• Marked hypotension
• Bronchospastic disorders or severe obstructive pulmonary disease
• Marked electrolyte imbalance
|5. MECHANISM OF ACTION|
Propafenone is a Class 1C antiarrhythmic drug with local anesthetic effects, and a direct stabilizing action on myocardial membranes. The electrophysiological effect of propafenone manifests itself in a reduction of upstroke velocity (Phase 0) of the monophasic action potential. In Purkinje fibers, and to a lesser extent myocardial fibers, propafenone reduces the fast inward current carried by sodium ions. Diastolic excitability threshold is increased and effective refractory period prolonged. Propafenone reduces spontaneous automaticity and depresses triggered activity.
Studies in anesthetized dogs and isolated organ preparations show that propafenone has beta-sympatholytic activity at about 1/50 the potency of propranolol. Clinical studies employing isoproterenol challenge and exercise testing after single doses of propafenone indicate a beta-adrenergic blocking potency (per mg) about 1/40 that of propranolol in man. In clinical trials, resting heart rate decreases of about 8% were noted at the higher end of the therapeutic plasma concentration range. At very high concentrations in vitro, propafenone can inhibit the slow inward current carried by calcium, but this calcium antagonist effect probably does not contribute to antiarrhythmic efficacy. Propafenone has local anesthetic activity approximately equal to procaine.
|6. USE IN SPECIFIC POPULATIONS|
6.1 Usage in Pregnancy
Pregnancy Category C
There are no adequate and well-controlled studies in pregnant women. Propafenone should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Animal Data: Teratogenic Effects: Propafenone HCl has been shown to be embryotoxic (decreased survival) in rabbits and rats when given in oral maternally toxic doses of 150 mg/kg/day (about 3 times the maximum recommended human dose [MRHD] on a mg/m2 basis) and 600 mg/kg/day (about 6 times the MRHD on a mg/m2 basis, respectively. Although maternally tolerated doses (up to 270 mg/kg/day, about 3 times the MRHD on a mg/m2 basis) produced no evidence of embryotoxicity in rats, post-implantation loss was elevated in all rabbit treatment groups (doses as low as 15 mg/kg/day, about 1/3 the MRHD on a mg/m2 basis). There are no adequate and well-controlled studies in pregnant women. Propafenone HCl should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
In a study in which female rats received daily oral doses of propafenone HCl from mid-gestation through weaning of their offspring, doses as low as 90 mg/kg/day (equivalent to the MRHD on a mg/m2 basis) produced increases in maternal deaths. Doses of 360 or more mg/kg/day (4 or more times the MRHD on a mg/m2 basis) resulted in reductions in neonatal survival, body weight gain and physiological development.
6.2 Labor and Delivery
It is not known whether the use of propafenone during labor or delivery has immediate or delayed adverse effects on the fetus, or whether it prolongs the duration of labor or increases the need for forceps delivery or other obstetrical intervention.
6.3 Nursing Mothers
Propafenone is excreted in human milk. Because of the potential for serious adverse reactions in nursing infants from propafenone, decide whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.
6.4 Pediatric Use
The safety and effectiveness of propafenone HCl in pediatric patients have not been established.
6.5 Geriatric Use
Clinical studies of propafenone HCl did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.
|7. WARNINGS AND PRECAUTIONS|
7.1 Proarrhythmic Effects
Propafenone has caused new or worsened arrhythmias. Such proarrhythmic effects include sudden death and life-threatening ventricular arrhythmias such as ventricular fibrillation, ventricular tachycardia, asystole and torsade de pointes. It may also worsen premature ventricular contractions or supraventricular arrhythmias, and it may prolong the QT interval. It is therefore essential that each patient given propafenone be evaluated electrocardiographically prior to and during therapy to determine whether the response to propafenone supports continued treatment. Because propafenone prolongs the QRS interval in the electrocardiogram, changes in the QT interval are difficult to interpret.
In a U.S. uncontrolled, open label, multicenter trial in patients with symptomatic supraventricular tachycardia (SVT), 1.9% (9/474) of these patients experienced ventricular tachycardia (VT) or ventricular fibrillation (VF) during the study. However, in 4 of the 9 patients, the ventricular tachycardia was of atrial origin. Six of the nine patients that developed ventricular arrhythmias did so within 14 days of onset of therapy. About 2.3% (11/474) of all patients had a recurrence of SVT during the study which could have been a change in the patients’ arrhythmia behavior or could represent a proarrhythmic event. Case reports in patients treated with propafenone for atrial fibrillation/flutter have included increased premature ventricular contractions (PVCs), VT, VF, torsade de pointes, asystole, and death.
Overall in clinical trials with propafenone (which included patients treated for ventricular arrhythmias, atrial fibrillation/flutter, and PSVT), 4.7% of all patients had new or worsened ventricular arrhythmia possibly representing a proarrhythmic event (0.7% was an increase in PVCs; 4.0% a worsening, or new appearance, of VT or VF). Of the patients who had worsening of VT (4%), 92% had a history of VT and/or VT/VF, 71% had coronary artery disease, and 68% had a prior myocardial infarction. The incidence of proarrhythmia in patients with less serious or benign arrhythmias, which include patients with an increase in frequency of PVCs, was 1.6%. Although most proarrhythmic events occurred during the first week of therapy, late events also were seen and the CAST study [see Boxed Warning: Mortality] suggests that an increased risk of proarrythmia is present throughout treatment.
In a study of sustained-release propafenone (propafenone SR), there were too few deaths to assess the long term risk to patients. There were 5 deaths, 3 in the pooled propafenone SR group (0.8%) and 2 in the placebo group (1.6%). In the overall propafenone SR and propafenone immediate-release database of 8 studies, the mortality rate was 2.5% per year on propafenone and 4.0% per year on placebo. Concurrent use of propafenone with other antiarrhythmic agents has not been well studied.
7.2 Unmasking Brugada Syndrome
Brugada Syndrome may be unmasked after exposure to propafenone. Perform an ECG after initiation of propafenone, and discontinue the drug if changes are suggestive of Brugada Syndrome [see Contraindications (4)].
7.3 Use with Drugs that Prolong the QT Interval and Antiarrhythmic Agents
The use of propafenone in conjunction with other drugs that prolong the QT interval has not been extensively studied. Such drugs may include many antiarrhythmics, some phenothiazines, tricyclic antidepressants, and oral macrolides. Withhold Class IA and III antiarrhythmic agents for at least 5 half-lives prior to dosing with propafenone. Avoid the use of propafenone with Class IA and III antiarrhythmic agents (including quinidine and amiodarone). There is only limited experience with the concomitant use of Class IB or IC antiarrhythmics.
7.4 Drug Interactions: Simultaneous Use with Inhibitors of Cytochrome P450 Isoenzymes 2D6 and 3A4
Propafenone is metabolized by CYP2D6, CYP3A4, and CYP1A2 isoenzymes. Approximately 6% of Caucasians in the U.S. population are naturally deficient in CYP2D6 activity and to a somewhat lesser extent in other demographic groups. Drugs that inhibit these CYP pathways (such as desipramine, paroxetine, ritonavir, sertraline for CYP2D6; ketoconazole, erythromycin, saquinavir, and grapefruit juice for CYP3A4; and amiodarone and tobacco smoke for CYP1A2) can be expected to cause increased plasma levels of propafenone.
Increased exposure to propafenone may lead to cardiac arrhythmias and exaggerated beta-adrenergic blocking activity. Because of its metabolism, the combination of CYP3A4 inhibition and either CYP2D6 deficiency or CYP2D6 inhibition in users of propafenone is potentially hazardous. Therefore, avoid simultaneous use of propafenone with both a CYP2D6 inhibitor and a CYP3A4 inhibitor.
7.5 Use in Patients with a History of Heart Failure
Propafenone exerts a negative inotropic activity on the myocardium as well as beta blockade effects and may provoke overt heart failure.
In clinical trial experience with propafenone, new or worsened congestive heart failure (CHF) has been reported in 3.7% of patients with ventricular arrhythmia; of those 0.9% were considered probably or definitely related to propafenone HCl. Of the patients with CHF probably related to propafenone, 80% had preexisting heart failure and 85% had coronary artery disease. CHF attributable to propafenone HCl developed rarely (< 0.2%) in ventricular arrhythmia patients who had no previous history of CHF. CHF occurred in 1.9% of patients studied with PAF or PSVT.
In a U.S. trial of propafenone SR in patients with symptomatic AF, heart failure was reported in 4 (1.0%) patients receiving propafenone SR (all doses), compared to 1 (0.8%) patient receiving placebo.
7.6 Conduction Disturbances
Propafenone slows atrioventricular conduction and may also cause dose-related first degree AV block. Average PR interval prolongation and increases in QRS duration are also dose-related. Do not give propafenone to patients with atrioventricular and intraventricular conduction defects in the absence of a pacemaker [see Contraindications (4)].
The incidence of first degree, second degree, and third degree AV block observed in 2,127 ventricular arrhythmia patients was 2.5%, 0.6%, and 0.2%, respectively. Development of second or third degree AV block requires a reduction in dosage or discontinuation of propafenone HCl. Bundle branch block (1.2%) and intraventricular conduction delay (1.1%) have been reported in patients receiving propafenone. Bradycardia has also been reported (1.5%). Experience in patients with sick sinus node syndrome is limited and these patients should not be treated with propafenone.
In a U.S. trial in 523 patients with a history of symptomatic AF treated with propafenone SR, sinus bradycardia (rate < 50 beats/min) was reported with the same frequency with propafenone SR and placebo.
7.7 Effects on Pacemaker Threshold
Propafenone may alter both pacing and sensing thresholds of implanted pacemakers and defibrillators. During and after therapy, monitor and re-program these devices accordingly.
Agranulocytosis has been reported in patients receiving propafenone. Generally, the agranulocytosis occurred within the first 2 months of propafenone therapy and upon discontinuation of therapy, the white count usually normalized by 14 days. Unexplained fever or decrease in white cell count, particularly during the initial 3 months of therapy, warrant consideration of possible agranulocytosis or granulocytopenia. Instruct patients to report promptly any signs of infection such as fever, sore throat, or chills.
7.9 Use in Patients with Hepatic Dysfunction
Propafenone is highly metabolized by the liver. Severe liver dysfunction increases the bioavailability of propafenone to approximately 70% compared to 3 to 40% in patients with normal liver function. In 8 patients with moderate to severe liver disease, the mean half-life was approximately 9 hours. Increased bioavailability of propafenone in these patients may result in excessive accumulation. Carefully monitor patients with impaired hepatic function for excessive pharmacological effects [see Overdosage (9)].
7.10 Use in Patients with Renal Dysfunction
Approximately 50% of propafenone metabolites are excreted in the urine following administration of propafenone.
In patients with impaired renal function, monitor for signs of overdosage [see Overdosage (9)].
7.11 Use in Patients with Myasthenia Gravis
Exacerbation of myasthenia gravis has been reported during propafenone therapy.
7.12 Elevated ANA Titers
Positive ANA titers have been reported in patients receiving propafenone. They have been reversible upon cessation of treatment and may disappear even in the face of continued propafenone therapy. These laboratory findings were usually not associated with clinical symptoms, but there is one published case of drug-induced lupus erythematosis (positive rechallenge); it resolved completely upon discontinuation of therapy. Carefully evaluate patients who develop an abnormal ANA test and, if persistent or worsening elevation of ANA titers is detected, consider discontinuing therapy.
7.13 Impaired Spermatogenesis
Reversible disorders of spermatogenesis have been demonstrated in monkeys, dogs and rabbits after high dose intravenous administration of propafenone. Evaluation of the effects of short-term propafenone administration on spermatogenesis in 11 normal subjects suggested that propafenone produced a reversible, short-term drop (within normal range) in sperm count.
|8. ADVERSE REACTIONS|
8.1 Clinical Trials Experience
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.
Adverse reactions associated with propafenone HCl occur most frequently in the gastrointestinal, cardiovascular, and central nervous systems. About 20% of patients treated with propafenone HCl have discontinued treatment because of adverse reactions.
Adverse reactions reported for >1.5% of 474 SVT patients who received propafenone in U.S. clinical trials are presented in the following table by incidence and percent discontinuation, reported to the nearest percent.
Table 1: Adverse Reactions Reported for >1.5% of SVT Patients
In controlled trials in patients with ventricular arrhythmia, the most common reactions reported for propafenone and more frequent than on placebo were unusual taste, dizziness, first degree AV block, intraventricular conduction delay, nausea and/or vomiting, and constipation. Headache was relatively common also, but was not increased compared to placebo. Other reactions reported more frequently than on placebo or comparator and not already reported elsewhere included anxiety, angina, second degree AV block, bundle branch block, loss of balance, congestive heart failure, and dyspepsia.
Adverse reactions reported for ≥ 1% of 2,127 ventricular arrhythmia patients who received propafenone in U.S. clinical trials were evaluated by daily dose. The most common adverse reactions appeared dose-related (but note that most patients spent more time at the larger doses), especially dizziness, nausea and/or vomiting, unusual taste, constipation, and blurred vision. Some less common reactions may also have been dose-related such as first degree AV block, congestive heart failure, dyspepsia, and weakness. Other adverse reactions included rash, syncope, chest pain, abdominal pain, ataxia, and hypotension.
In addition, the following adverse reactions were reported less frequently than 1% either in clinical trials or in marketing experience. Causality and relationship to propafenone therapy cannot necessarily be judged from these events.
Cardiovascular System: Atrial flutter, AV dissociation, cardiac arrest, flushing, hot flashes, sick sinus syndrome, sinus pause or arrest, supraventricular tachycardia.
Nervous System: Abnormal dreams, abnormal speech, abnormal vision, confusion, depression, memory loss, numbness, paresthesias, psychosis/mania, seizures (0.3%), tinnitus, unusual smell sensation, vertigo.
Gastrointestinal: Cholestasis , elevated liver enzymes (alkaline phosphatase, serum transaminases) , gastroenteritis, hepatitis .
Hematologic: Agranulocytosis, anemia, bruising, granulocytopenia, leukopenia, purpura, thrombocytopenia.
Other: Alopecia, eye irritation, impotence, increased glucose, positive ANA (0.7%), muscle cramps, muscle weakness, nephrotic syndrome, pain, pruritus.
8.2 Postmarketing Experience
The following adverse reactions have been identified during post-approval use of propafenone. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.
Gastrointestinal: A number of patients with liver abnormalities associated with propafenone therapy have been reported in post-marketing experience. Some appeared due to hepatocellular injury, some were cholestatic and some showed a mixed picture. Some of these reports were simply discovered through clinical chemistries, others because of clinical symptoms including fulminant hepatitis and death. One case was rechallenged with a positive outcome.
Blood and Lymphatic System: Increased bleeding time
Immune System: lupus erythematosis
Nervous System: Apnea, coma
Renal and Urinary: Hyponatremia/inappropriate ADH secretion, kidney failure
The symptoms of overdosage may include hypotension, somnolence, bradycardia, intraatrial and intraventricular conduction disturbances, and rarely convulsions and high grade ventricular arrhythmias. Defibrillation as well as infusion of dopamine and isoproterenol have been effective in controlling abnormal rhythm and blood pressure. Convulsions have been alleviated with intravenous diazepam. General supportive measures such as mechanical respiratory assistance and external cardiac massage may be necessary.
The hemodialysis of propafenone in patients with an overdose is expected to be of limited value in the removal of propafenone as a result of both its high protein binding (>95%) and large volume of distribution.
|10. DRUG INTERACTIONS|
10.1 CYP2D6 and CYP3A4 Inhibitors
Drugs that inhibit CYP2D6 (such as desipramine, paroxetine, ritonavir, or sertraline) and CYP3A4 (such as ketoconazole, ritonavir, saquinavir, erythromycin, or grapefruit juice) can be expected to cause increased plasma levels of propafenone. The combination of CYP3A4 inhibition and either CYP2D6 deficiency or CYP2D6 inhibition with administration of propafenone may increase the risk of adverse reactions, including proarrhythmia. Therefore, simultaneous use of propafenone with both a CYP2D6 inhibitor and a CYP3A4 inhibitor should be avoided [see Warnings and Precautions (7.4) and Dosage and Administration (3)].
Amiodarone: Concomitant administration of propafenone and amiodarone can affect conduction and repolarization and is not recommended.
Cimetidine: Concomitant administration of propafenone immediate release tablets and cimetidine in 12 healthy subjects resulted in a 20% increase in steady-state plasma concentrations of propafenone.
Fluoxetine: Concomitant administration of propafenone and fluoxetine in extensive metabolizers increased the S-propafenone Cmax and AUC by 39% and 50% and the R propafenone Cmax and AUC by 71% and 50%.
Quinidine: Small doses of quinidine completely inhibit the CYP2D6 hydroxylation metabolic pathway, making all patients, in effect, slow metabolizers. Concomitant administration of quinidine (50 mg three times daily) with 150 mg immediate release propafenone three times daily decreased the clearance of propafenone by 60% in extensive metabolizers, making them slow metabolizers. Steady-state plasma concentrations more than doubled for propafenone, and decreased 50% for 5-OH-propafenone. A 100 mg dose of quinidine tripled steady state concentrations of propafenone. Avoid concomitant use of propafenone and quinidine.
Rifampin: Concomitant administration of rifampin and propafenone in extensive metabolizers decreased the plasma concentrations of propafenone by 67% with a corresponding decrease of 5-OH-propafenone by 65%. The concentrations of norpropafenone increased by 30%. In slow metabolizers, there was a 50% decrease in propafenone plasma concentrations and increased the AUC and Cmax of norpropafenone by 74% and 20%, respectively. Urinary excretion of propafenone and its metabolites decreased significantly. Similar results were noted in elderly patients: Both the AUC and Cmax propafenone decreased by 84%, with a corresponding decrease in AUC and Cmax of 5-OH-propafenone by 69% and 57%.
Concomitant use of propafenone and digoxin increased steady-state serum digoxin exposure (AUC) in patients by 60% to 270%, and decreased the clearance of digoxin by 31% to 67%. Monitor plasma digoxin levels of patients receiving propafenone and adjust digoxin dosage as needed.
The concomitant administration of propafenone and warfarin increased warfarin plasma concentrations at steady state by 39% in healthy volunteers and prolonged the prothrombin time (PT) in patients taking warfarin. Adjust the warfarin dose as needed by monitoring INR (international normalized ratio).
Orlistat may limit the fraction of propafenone available for absorption. In post marketing reports, abrupt cessation of orlistat in patients stabilized on propafenone has resulted in severe adverse events including convulsions, atrioventricular block and acute circulatory failure.
Concomitant use of propafenone and propranolol in healthy subjects increased propranolol plasma concentrations at steady state by 113%. In 4 patients, administration of metoprolol with propafenone increased the metoprolol plasma concentrations at steady state by 100% to 400%. The pharmacokinetics of propafenone was not affected by the coadministration of either propranolol or metoprolol. In clinical trials using propafenone immediate release tablets, patients who were receiving beta-blockers concurrently did not experience an increased incidence of side effects.
No significant effects on the pharmacokinetics of propafenone or lidocaine have been seen following their concomitant use in patients. However, concomitant use of propafenone and lidocaine has been reported to increase the risks of central nervous system side effects of lidocaine.
Propafenone HCl is nearly completely absorbed after oral administration with peak plasma levels occurring approximately 3.5 hours after administration in most individuals. Propafenone exhibits extensive saturable presystemic biotransformation (first pass effect) resulting in a dose dependent and dosage form dependent absolute bioavailability; e.g., a 150 mg tablet had absolute bioavailability of 3.4%, while a 300 mg tablet had absolute bioavailability of 10.6%. A 300 mg solution which was rapidly absorbed, had absolute bioavailability of 21.4%. At still larger doses, above those recommended, bioavailability increases still further.
Propafenone HCl follows a nonlinear pharmacokinetic disposition presumably due to saturation of first pass hepatic metabolism as the liver is exposed to higher concentrations of propafenone and shows a very high degree of interindividual variability. For example, for a three-fold increase in daily dose from 300 to 900 mg/day there is a tenfold increase in steady-state plasma concentration. The top 25% of patients given 375 mg/day, however, had a mean concentration of propafenone larger than the bottom 25%, and about equal to the second 25%, of patients given a dose of 900 mg. Although food increased peak blood level and bioavailability in a single dose study, during multiple dose administration of propafenone to healthy volunteers food did not change bioavailability significantly.
Following intravenous administration of propafenone, plasma levels decline in a bi-phasic manner consistent with a 2 compartment pharmacokinetic model. The average distribution half-life corresponding to the first phase was about 5 minutes. The volume of the central compartment was about 88 liters (1.1 L/kg) and the total volume of distribution about 252 liters.
In serum, propafenone is greater than 95% bound to proteins within the concentration range of 0.5 to 2 μg/mL.
There are two genetically determined patterns of propafenone metabolism. In over 90% of patients, the drug is rapidly and extensively metabolized with an elimination half-life from 2–10 hours. These patients metabolize propafenone into two active metabolites: 5- hydroxypropafenone which is formed by CYP2D6 and N-depropylpropafenone which is formed by both CYP3A4 and CYP1A2.
In less than 10% of patients (and in any patient also receiving quinidine, see PRECAUTIONS), metabolism of propafenone is slower because the 5-hydroxy metabolite is not formed or is minimally formed. The estimated propafenone elimination half-life ranges from 10–32 hours. Decreased ability to form the 5-hydroxy metabolite of propafenone is associated with a diminished ability to metabolize debrisoquine and a variety of other drugs (encainide, metoprolol, dextromethorphan). In these patients, the N-depropylpropafenone occurs in quantities comparable to the levels occurring in extensive metabolizers. In slow metabolizers propafenone pharmacokinetics are linear.
There are significant differences in plasma concentrations of propafenone in slow and extensive metabolizers, the former achieving concentrations 1.5 to 2.0 times those of the extensive metabolizers at daily doses of 675–900 mg/day. At low doses the differences are greater, with slow metabolizers attaining concentrations more than five times that of extensive metabolizers. Because the difference decreases at high doses and is mitigated by the lack of the active 5-hydroxy metabolite in the slow metabolizers, and because steady-state conditions are achieved after 4–5 days of dosing in all patients, the recommended dosing regimen is the same for all patients. The greater variability in blood levels require that the drug be titrated carefully in patients with close attention paid to clinical and ECG evidence of toxicity (See DOSAGE AND ADMINISTRATION).
Stereochemistry: Propafenone is a racemic mixture. The R- and S-enantiomers of propafenone display stereoselective disposition characteristics. In vitro and in vivo studies have shown that the R-isomer of propafenone is cleared faster than the S-isomer via the 5- hydroxylation pathway (CYP2D6). This results in a higher ratio of S-propafenone to R-propafenone at steady state. Both enantiomers have equivalent potency to block sodium channels; however, the S-enantiomer is a more potent β-antagonist than the R-enantiomer. Following administration of propafenone immediate-release tablets, the S/R ratio for the area under the plasma concentration-time curve was about 1.7. In addition, no difference in the average values of the S/R ratios is evident between genotypes or over time.
Hepatic Impairment: Decreased liver function increases the bioavailability of propafenone. Absolute bioavailability of propafenone immediate-release tablets is inversely related to indocyanine green clearance, reaching 60-70% at clearances of 7 mL/min and below. Protein binding decreases to about 88% in patients with severe hepatic dysfunction. The clearance of propafenone is reduced and the elimination half-life increased in patients with significant hepatic dysfunction [see Warnings and Precautions (7.9)].
|12. HOW SUPPLIED/STORAGE AND HANDLING|
1) How Available:
a) Brand name: RYTHMOL, by GLAXOSMITHKLINE LLC.
b) International brand name: RYTMONORM, by ABBOTT (Outside of USA).
c) Generic drugs: Propafenone hydrochloride, by various manufacturers.
2) How Supplied:
Propafenone hydrochloride tablets (by Mutual Pharm) are supplied as follows:
Propafenone hydrochloride tablets 150 mg, white, round, scored, film-coated, debossed MP 511
Bottles of 30 NDC 53489-551-07
Bottles of 100 NDC 53489-551-01
Bottles of 250 NDC 53489-551-03
Bottles of 500 NDC 53489-551-05
Bottles of 1000 NDC 53489-551-10
Propafenone hydrochloride tablets 225 mg, white, round, scored, film-coated, debossed MP 512
Bottles of 30 NDC 53489-552-07
Bottles of 100 NDC 53489-552-01
Bottles of 250 NDC 53489-552-03
Bottles of 500 NDC 53489-552-05
Bottles of 1000 NDC 53489-552-10
Propafenone hydrochloride tablets 300 mg, white, round, scored, film-coated, debossed MP 513
Bottles of 30 NDC 53489-553-07
Bottles of 100 NDC 53489-553-01
Bottles of 250 NDC 53489-553-03
Bottles of 500 NDC 53489-553-05
Bottles of 1000 NDC 53489-553-10
3) Storage and Handling:
Store at 20° to 25°C (68° to 77°F). [see USP Controlled Room Temperature].
DISPENSE IN TIGHT, LIGHT-RESISTANT CONTAINER