Side Effects of Rythmol (propafenone)

Rythmol (propafenone) is an antiarrhythmic agent used in patients with life-threatening ventricular arrhythmias, such as ventricular tachycardia.

Rythmol is effective in

• atrial tachycardia,
• AV nodal tachycardia, and
• bypass tract tachycardias.

Rythmol is also effective in suppressing the recurrence of atrial fibrillation and supra-ventricular tachycardia once normal sinus rhythm has been restored. Rythmol is at least as effective as any other type I agent in converting atrial fibrillation to normal sinus rhythm.

Common side effects of Rythmol include

• dizziness,
• blurred vision,
• loss of appetite,
• unusual taste,
• fatigue,
• constipation,
• headache,
• reduced cardiac conduction,
• nausea, and
• vomiting.

Serious side effects of Rythmol include

• chest pain,
• heart palpitations,
• increased rate of cardiac arrest,
• abnormal heart beats,
• aggravation of myasthenia gravis,
• increased rate of death,
• congestive heart failure, and
• serious life-threatening irregular heart rhythms (ventricular arrhythmias or pro-arrhythmia) or heart block. 

Drug interactions of Rythmol include quinidine and fluoxetine, which inhibit the metabolism of Rythmol.

Rythmol increases the levels of

• digoxin,
• warfarin, and
• beta blockers.

Rifampin increases the metabolism of Rythmol, decreasing blood levels of Rythmol. Orlistat may reduce the absorption of Rythmol.

Stopping orlistat in patients stabilized on Rythmol may result in Rythmol toxicity because more Rythmol will be absorbed after discontinuation of orlistat.

Rythmol may alter pacing and sensing thresholds of pacemakers and defibrillators.

These devices should be re-programmed and closely monitored. Safety and efficacy of Rythmol in pregnant women have not been established. Rythmol is excreted in breast milk. Mothers should decide whether to stop breastfeeding or discontinue Rythmol.

Common side effects of propafenone are:

• Dizziness
• Blurred vision
• Anorexia
• Unusual taste
• Fatigue
• Constipation
• Headache
• Reduced cardiac conduction
• Nausea and vomiting

Serious side effects of propafenone include:

• Chest pain
• Heart palpitations
• Increased rate of cardiac arrest
• Abnormal heart beats
• Aggravation of myasthenia gravis
• Increased rate of death
• Congestive heart failure

Because of its beta blocking activity, propafenone must be used with caution in patients with

• weak heart muscle (congestive heart failure),
• slow heart rate,
• any form of heart electrical conduction block,
• low blood pressure, or
• asthma.

The most serious side effect of propafenone is the causing of serious life-threatening irregular heart rhythms (ventricular arrhythmias or pro-arrhythmia) or heart block. It is for this reason that propafenone is started and doses increased while patients are hospitalized in a monitored setting.

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 Rythmol occur most frequently in the gastrointestinal, cardiovascular, and central nervous systems. About 20% of patients treated with Rythmol have discontinued treatment because of adverse reactions.

Adverse reactions reported for > 1.5% of 474 SVT patients who received Rythmol in U.S. clinical trials are presented in Table 1 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 Rythmol 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.

Postmarketing Experience

The following adverse reactions have been identified during post-approval use of Rythmol. 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

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 Rythmol with both a CYP2D6 inhibitor and a CYP3A4 inhibitor should be avoided.

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%.

Digoxin

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.

Warfarin

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

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.

Beta-Antagonists

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.

Lidocaine

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.