Rythmol SR

Name: Rythmol SR


Black Box Warnings

NHLBI’s Cardiac Arrhythmia Suppression Trial (CAST): Excessive mortality or nonfatal cardiac arrest (7.7%) shown with encainide or flecainide, compared with placebo (3%)

Applicability of CAST results to other populations (eg, patients without recent MI) is uncertain; therefore, reserve use of class IC antiarrhythmics for life-threatening ventricular arrhythmias

Considering known proarrhythmic properties of propafenone and lack of evidence of improved survival for any antiarrhythmic drug in patients without life-threatening arrhythmias, use should be reserved for patients with life-threatening ventricular arrhythmias



Bradycardia, asthma/bronchospastic disorders or severe obstructive pulmonary disease, marked hypotension, cardiogenic shock, intraventricular disorders of impulse generation and/or conduction including sick sinus node and syndrome AV block (unless artificial pacemaker present), electrolyte imbalances, CHF, severe hypotension, myasthenia gravis

Known Brugada syndrome

Concomitant ritonavir therapy


May alter pacemaker thresholds

Elevated ANA titers reported with use; may consider discontinuing therapy in symtomatic patients with positive ANA titers

Use caution in patients with hematologic disorders, myasthenia gravis (may exacerbate condition), hepatic/renal impairment

Use with caution in patients with hypersensitivity to propranolol

There is a potential for increased mortality post-MI, as with encainide and flecainide (other class ICs)

May cause life-threatening drug-induced arrhythmias including assytole, ventricular fibrillation, ventricular tachycardia, and torsade de pointes

Through CYP3A inhibition, grapefruit juice consumption may decrease elimination (ie, increase serum levels)

Correct electrolyte imbalance, especially hypomagnesemia or hypokalemia before initiating therapy and throughout

Plasma concentration has poor correlation to antiarrhythmia effect

New or worsening HF may occur

Slows AV conduction and may cause AV block

Brugada syndrome may be unmasked after exposure to propafenone; perform ECG after initiation and discontinue the drug if changes are suggestive of Brugada Syndrome

Agranulocytosis reported (most within first 2 months of treatment)

Highly metabolized by liver; severe liver impairment increases bioavailability by 70%

What special precautions should I follow?

Before taking propafenone,

  • tell your doctor and pharmacist if you are allergic to propafenone, any other medications, or any of the ingredients in propafenone tablets or extended-release capsules. Ask your doctor or pharmacist for a list of the ingredients.
  • tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: anticoagulants ('blood thinners') such as warfarin (Coumadin); certain antibiotics such as azithromycin (Zithromax), clarithromycin (Biaxin, in Prevpac), and erythromycin (E.E.S., others);antihistamines; beta-blockers such as atenolol (Tenormin), carteolol (Cartrol), labetalol (Normodyne, Trandate), metoprolol (Lopressor), nadolol (Corgard), propranolol (Inderal), sotalol (Betapace), and timolol (Blocadren); certain antidepressants such as desipramine (Norpramin) and imipramine (Tofranil);cimetidine (Tagamet); cisapride (Propulsid) (not available in the U.S.); digoxin (Lanoxin); haloperidol (Haldol); ketoconazole (Nizoral); lidocaine; medications for irregular heartbeat such as amiodarone (Cordarone, Pacerone), bepredil (not available in the U.S.), dofetilide (Tikosyn), disopyramide (Norpace), ibutilide (Corvert), procainamide, and quinidine (Quinaglute, others). medications for mental illness and nausea; orlistat (Alli, Xenical); ritonavir (Norvir);rifampin (Rifadin, Rimactane); saquinavir (Invirase); selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine (Prozac, Sarafem, in Symbyax), paroxetine (Paxil, Pexeva) and sertraline (Zoloft); and venlafaxine (Effexor).
  • tell your doctor if you have excessive diarrhea, sweating, vomiting, loss of appetite, or decreased thirst and if you have or have ever had a slow heartbeat; low blood pressure; low or high levels of sodium, potassium, chloride, or bicarbonate in your blood; heart failure; or asthma or any other condition that causes your airways to become narrow. Your doctor may tell you not to take propafenone.
  • in addition to the conditions listed in the IMPORTANT WARNING section, tell your doctor if you have or have ever had a pacemaker; myasthenia gravis (a disorder of the nervous system that causes muscle weakness),or liver or kidney disease,
  • tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking propafenone, call your doctor.
  • if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking propafenone.
  • you should know that this medication may make you drowsy or dizzy. Do not drive a car or operate machinery until you know how it affects you.
  • tell your doctor if you use tobacco products. Cigarette smoking may decrease the effectiveness of this medication.

What brand names are available for propafenone?

Rythmol, Rythmol SR

Clinical pharmacology

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 with the immediate release formulation, 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. Moreover, propafenone inhibits a variety of cardiac potassium currents in in vitro studies (i.e. the transient outward, the delayed rectifier, and the inward rectifier current). Propafenone has local anesthetic activity approximately equal to procaine. Compared to propafenone, the main metabolite, 5-hydroxypropafenone, has similar sodium and calcium channel activity, but about 10 times less beta-blocking activity (N-depropylpropafenone has weaker sodium channel activity but equivalent affinity for beta-receptors).


Electrophysiology: Electrophysiology studies in patients with ventricular tachycardia have shown that propafenone prolongs atrioventricular conduction while having little or no effect on sinus node function. Both atrioventricular nodal conduction time (AH interval) and His-Purkinje conduction time (HV interval) are prolonged. Propafenone has little or no effect on the atrial functional refractory period, but AV nodal functional and effective refractory periods are prolonged. In patients with Wolff-Parkinson-White syndrome, RYTHMOL immediate release tablets reduce conduction and increase the effective refractory period of the accessory pathway in both directions.

Electrocardiograms: Propafenone prolongs the PR and QRS intervals. Prolongation of the QRS interval makes it difficult to interpret the effect of propafenone on the QT interval.

Table 2. Mean Change ± SD in 12-Lead Electrocardiogram Results (RAFT)

  RYTHMOL SR Twice-Daily Dosing Placebo
225 mg 325 mg 425 mg
n=126 n=135 n=136 n=126
PR (ms) 9±22 12±23 21±24 1±16
QRS (ms) 4±14 6±15 6±15 -2±12
Heart rate 5±24 7±23 2±22 8±27
QTc* (ms) 2±30 5±36 6±37 5±35
*Calculated using Bazett's correction factor

In RAFT [see Clinical Studies], the distribution of the maximum changes in QTc compared to baseline over the study in each patient was similar in the RYTHMOL SR 225 mg twice daily, 325 mg twice daily, and 425 mg twice daily and placebo dose groups. Similar results were seen in the ERAFT study.

Table 3. Number of Patients According to the Range of Maximum QTc change compared to baseline over the study in each dose group (RAFT study).

Range maximum QTc change RYTHMOL SR Placebo
225 mg twice daily 325 mg twice daily 425 mg twice daily  
n=119 n=129 n=123 n=100
n(%) n(%) n(%) n(%)
> 20% 1 (1) 6 (5) 3 (2) 5 (4)
10-20% 19(16) 28 (22) 32 (26) 24 (20)
0 ≤ 10% 99 (83) 95 (74) 88 (72) 91 (76)

Hemodynamics: Studies in humans have shown that propafenone exerts a negative inotropic effect on the myocardium. Cardiac catheterization studies in patients with moderately impaired ventricular function (mean C.I.=2.61 L/min/m2), utilizing intravenous propafenone infusions (loading dose of 2 mg/kg over 10 min+ followed by 2 mg/min for 30 min) that gave mean plasma concentrations of 3.0 µg/mL (a dos e that produces plasma levels of propafenone greater than does recommended oral dosing), showed significant increases in pulmonary capillary wedge pressure, systemic and pulmonary vascular resistances and depression of cardiac output and cardiac index.


Absorption/Bioavailability: Maximal plasma levels of propafenone are reached between 3 to 8 hours following the administration of RYTHMOL SR. Propafenone is known to undergo extensive and saturable presystemic biotransformation which results in a dose and dosage form dependent absolute bioavailability; e.g., a 150 mg immediate release tablet had an absolute bioavailability of 3.4%, while a 300 mg immediate release tablet had an absolute bioavailability of 10.6%. Absorption from a 300 mg solution dose was rapid, with an absolute bioavailability of 21.4%. At still larger doses, above those recommended, bioavailability of propafenone from immediate release tablets increased still further.

Relative bioavailability assessments have been performed between RYTHMOL SR capsules and RYTHMOL immediate release tablets. In extensive metabolizers, the bioavailability of propafenone from the SR formulation was less than that of the immediate release formulation as the more gradual release of propafenone from the prolonged-release preparations resulted in an increase of overall first pass metabolism [see Metabolism]. As a result of the increased first pass effect, higher daily doses of propafenone were required from the SR formulation relative to the immediate release formulation, to obtain similar exposure to propafenone. The relative bioavailability of propafenone from the 325 twice daily regimens of RYTHMOL SR approximates that of RYTHMOL immediate release 150 mg three times daily regimen. Mean exposure to 5-hydroxypropafenone was about 20-25% higher after SR capsule administration than after immediate release tablet administration.

Food increased the exposure to propafenone 4-fold after single dose administration of 425 mg of RYTHMOL SR. However, in the multiple dose study (425 mg dose BID), the difference between the fed and fasted state was not significant.

Distribution: 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 0.5-2 µg/mL

Metabolism: 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 (norpropafenone) which is formed by both CYP3A4 and CYP1A2. In less than 10% of patients, metabolism of propafenone is slower because the 5-hydroxy metabolite is not formed or is minimally formed. In these patients, 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 such as encainide, metoprolol, and dextromethorphan whose metabolism is mediated by the CYP2D6 isozyme. In these patients, the N-depropylpropafenone metabolite occurs in quantities comparable to the levels occurring in extensive metabolizers.

As a consequence of the observed differences in metabolism, administration of RYTHMOL SR to slow and extensive metabolizers results in significant differences in plasma concentrations of propafenone, with slow metabolizers achieving concentrations about twice those of the extensive metabolizers at daily doses of 850 mg/day. At low doses the differences are greater, with slow metabolizers attaining concentrations about 3 to 4 times higher than extensive metabolizers. In extensive metabolizers, saturation of the hydroxylation pathway (CYP2D6) results in greater-than-linear increases in plasma levels following administration of RYTHMOL SR capsules. In slow metabolizers, propafenone pharmacokinetics is linear. Because the difference decreases at high doses and is mitigated by the lack of the active 5-hydroxymetabolite in the slow metabolizers, and because steady-state conditions are achieved after 4 to 5 days of dosing in all patients, the recommended dosing regimen of RYTHMOL SR is the same for all patients. The larger inter-subject variability in blood levels require that the dose of the drug be titrated carefully in patients with close attention paid to clinical and ECG evidence of toxicity [see DOSAGE AND ADMINISTRATION].

The 5-hydroxypropafenone and norpropafenone metabolites have electrophysiologic properties similar to propafenone in vitro. In man after administration of RYTHMOL SR, the 5-hydroxypropafenone metabolite is usually present in concentrations less than 40% of propafenone. The norpropafenone metabolite is usually present in concentrations less than 10% of propafenone.

Inter-Subject Variability: With propafenone, there is a considerable degree of inter-subject variability in pharmacokinetics which is due in large part to the first pass hepatic effect and non-linear pharmacokinetics in extensive metabolizers. A higher degree of inter-subject variability in pharmacokinetic parameters of propafenone was observed following both single and multiple dose administration of RYTHMOL SR capsules. Inter-subject variability appears to be substantially less in the poor metabolizer group than in the extensive metabolizer group, suggesting that a large portion of the variability is intrinsic to CYP2D6 polymorphism rather than to the formulation.

Stereochemistry: RYTHMOL 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 RYTHMOL immediate release tablets or RYTHMOL SR capsules, the S/R ratio for the area under the plasma concentration-time curve was about 1.7. The S/R ratios of propafenone obtained after administration of 225, 325 and 425 mg RYTHMOL SR are independent of dose. In addition, no difference in the average values of the S/R ratios is evident between genotypes or over time.

Special Populations

Hepatic Impairment: Decreased liver function increases the bioavailability of propafenone. Absolute bioavailability assessments have not been determined for the RYTHMOL SR capsule formulation. Absolute bioavailability of RYTHMOL 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].

Animal Toxicology and/or Pharmacology

Renal and Hepatic Toxicitv in Animals: Renal changes have been observed in the rat following 6 months of oral administration of propafenone HC1 at doses of 180 and 360 mg/kg/day (about 2 and 4 times, respectively, the maximum recommended human daily dose [MRHD] on a mg/m2 basis). Both inflammatory and non-inflammatory changes in the renal tubules, with accompanying interstitial nephritis, were observed. These changes were reversible, as they were not found in rats allowed to recover for 6 weeks. Fatty degenerative changes of the liver were found in rats following longer durations of administration of propafenone HC1 at a dose of 270 mg/kg/day (about 3 times the MRHD on a mg/m2 basis). There were no renal or hepatic changes at 90 mg/kg/day equivalent to the MRHD on a mg/m2 basis).

Clinical Studies

RYTHMOL SR has been evaluated in patients with a history of electrocardiographically documented recurrent episodes of symptomatic AF in 2 randomized, double-blind, placebo controlled trials.

RAFT: In one US multicenter study (Rythmol SR Atrial Fibrillation Trial, RAFT), 3 doses of RYTHMOL SR (225 mg twice daily, 325 mg twice daily and 425 mg twice daily) and placebo were compared in 523 patients with symptomatic, episodic AF. The patient population in this trial was 59% male with a mean age of 63 years; 91% White and 6% Black. The patients had a median history of AF of 13 months, and documented symptomatic AF within 12 months of study entry. Over 90% were NYHA Class I, and 21% had a prior electrical cardioversion. At baseline, 24% were treated with calcium channel blockers, 37% with beta blockers, and 38% with digoxin. Symptomatic arrhythmias after randomization were documented by transtelephonic electrocardiogram and centrally read and adjudicated by a blinded adverse event committee. RYTHMOL SR administered for up to 39 weeks was shown to prolong significantly the time to the first recurrence of symptomatic atrial arrhythmia, predominantly AF, from Day 1 of randomization (primary efficacy variable) compared to placebo, as shown in Table 4.

Table 4: Analysis of Tachycardia-Free Period (Days) from Day 1 of Randomization

Parameter RYTHMOL SR Twice-Daily Dose  
225 mg
n (%)
325 mg
n (%)
425 mg
n (%)
n (%)
Patients completing with terminating event* 66 (52) 56 (41) 41 (30) 87 (69)
Comparison of tachycardia-free periods
Kaplan-Meier Media 112 291 NA† 41
  Range 0-285 0-293 0-300 0-289
  p- Value (Log-rank test) 0.014 < 0.0001 < 0.0001 --
Hazard Ratio compared to placebo 0.67 0.43 0.35 --
95% CI for Hazard Ratio (0.49, 0.93) (0.31,0.61) (0.24, 0.51) --
* Terminating events comprised 91% AF, 5% atrial flutter, and 4% PSVT.
† Not Applicable: Fewer than 50% of the patients had events. The median time is not calculable.

There was a dose response for RYTHMOL SR for the tachycardia-free period as shown in the proportional hazard analysis and the Kaplan-Meier curves presented in Figure 1.

Figure 1: RAFT Kaplan-Meier Analysis for the Tachycardia-free period from Day 1 of randomization

In additional analyses, RYTHMOL SR (225 mg twice daily, 325 mg twice daily, and 425 mg twice daily) was also shown to prolong time to the first recurrence of symptomatic AF from Day 5 (steady-state pharmacokinetics were attained). The antiarrhythmic effect of RYTHMOL SR was not influenced by age, gender, history of cardio version, duration of AF, frequency of AF or use of medication that lowers heart rate. Similarly, the antiarrhythmic effect of RYTHMOL SR was not influenced by the individual use of calcium channel blockers, beta-blockers or digoxin. Too few non-White patients were enrolled to assess the influence of race on effects of RYTHMOL SR (propafenone hydrochloride).

No difference in the average heart rate during the first recurrence of symptomatic arrhythmia between RYTHMOL SR and placebo was observed.

ERAFT: In a European multicenter trial [(European Rythmonorm SR Atrial Fibrillation Trial (ERAFT)], 2 doses of RYTHMOL SR (325 mg twice daily and 425 mg twice daily) and placebo were compared in 293 patients with documented electrocardiographic evidence of symptomatic paroxysmal AF. The patient population in this trial was 61% male, 100% White with a mean age of 61 years. Patients had a median duration of AF of 3.3 years, and 61% were taking medications that lowered heart rate. At baseline, 15% of the patients were treated with calcium channel blockers (verapamil and diltiazem), 42% with beta-blockers and 8% with digoxin. During a qualifying period of up to 28 days, patients had to have 1 ECG-documented incident of symptomatic AF. The double-blind treatment phase consisted of a 4 day loading period followed by a 91-day efficacy period. Symptomatic arrhythmias were documented by electrocardiogram monitoring.

In ERAFT, RYTHMOL SR was shown to prolong the time to the first recurrence of symptomatic atrial arrhythmia from Day 5 of randomization (primary efficacy analysis). The proportional hazard analysis revealed that both RYTHMOL SR doses were superior to placebo. The antiarrhythmic effect of propafenone SR was not influenced by age, gender, duration of AF, frequency of AF or use of medication that lowers heart rate. It was also not influenced by the individual use of calcium channel blockers, beta-blockers or digoxin. Too few non-White patients were enrolled to assess the influence of race on the effects of RYTHMOL SR. There was a slight increase in the incidence of centrally diagnosed asymptomatic AF or atrial flutter in each of the 2 RYTHMOL SR treatment groups compared to placebo.

What is the most important information i should know about propafenone (rythmol, rythmol sr)?

You should not use this medication if you are allergic to propafenone, or if you have untreated or uncontrolled congestive heart failure, a heart condition called "sick sinus syndrome" or "AV block" (unless you have a pacemaker), slow heartbeats or severely low blood pressure, an electrolyte imbalance, or a breathing disorder such as asthma.

Before you take propafenone, tell your doctor if you have congestive heart failure, liver or kidney disease, lupus, arthritis, myasthenia gravis, or if you have had a heart attack within the past 2 years.

Call your doctor at once if you have a serious side effect such as weak pulse, slow breathing, feeling like you might pass out, feeling short of breath, swelling, rapid weight gain, pale skin, easy bruising or bleeding, unusual weakness, confusion, unusual thoughts or behavior, or seizure.


  • Glaxo SmithKline Pharmaceuticals

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while taking Rythmol SR (propafenone)?

Grapefruit and grapefruit juice may interact with propafenone and lead to unwanted side effects. Avoid the use of grapefruit products while taking propafenone.

What other drugs will affect Rythmol SR (propafenone)?

Many drugs can interact with propafenone. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any you start or stop using, especially:

  • isoniazid;

  • nefazodone;

  • orlistat (alli, Xenical);

  • warfarin (Coumadin, Jantoven);

  • an antibiotic--ciprofloxacin, clarithromycin, enoxacin, telithromycin;

  • an antidepressant--bupropion (Wellbutrin), fluoxetine (Prozac), paroxetine (Paxil);

  • antifungal medicine--itraconazole, ketoconazole, posaconazole, voriconazole;

  • heart medication--digoxin, nicardipine, lidocaine, quinidine; or

  • antiviral medicine to treat hepatitis C or HIV/AIDS--atazanavir, boceprevir, cobicistat, delavirdine, fosamprenavir, indinavir, nelfinavir, ritonavir, saquinavir.

This list is not complete and many other drugs can interact with propafenone. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Give a list of all your medicines to any healthcare provider who treats you.

Uses of Rythmol SR

  • It is used to treat certain types of abnormal heartbeats.