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Side Effects of Propafenone (Rythmol)


Description: Propafenone, commonly known by its trade name Rythmol, is an antiarrhythmic drug (it prevents irregular heart rhythm). It is frequently used in the treatment of conditions that cause life-threatening increases in heart rates.

Serious Rythmol Side Effects

A black box warning from the FDA has been reported for Rythmol for the increased rate of death or reversed cardiac arrest rate arrhythmias as reported by the Rythmol label as reported by FDA (2013). Other serious adverse reactions include: proarrhythmic effects including sudden death and life-threatening ventricular arrhythmias, ventricular tachycardia, asystole and torsade de pointes. It may also worsen premature ventricular contractions or supraventricular arrhythmias, and it may prolong the QT interval.

Common Side Effects of Rythmol

According to the Rythmol label, common adverse reactions include:

  • Dizziness
  • Headaches
  • Ataxia (loss of control of bodily movements)
  • Fatigue
  • Constipation
  • Metallic taste
  • Nausea
  • Vomiting
  • Dyspnea (difficulty breathing)
  • Wheezing
  • Blurred vision
  • Eye irritation

Less Common Side Effects of Rythmol

These reactions have been reported but in low frequency according to the Rythmol label:abdominal distension, abdominal pain, gingival bleeding, glossitis, glossodynia, gum pain, halitosis, intestinal obstruction, melena, mouth ulceration, pancreatitis, peptic ulcer, rectal bleeding, sore throat abnormal heart sounds, abnormal pulse, carotid bruit, decreased blood chloride, decreased blood pressure, decreased blood sodium, decreased hemoglobin, decreased neutrophil count, decreased platelet count, decreased prothrombin level, increased blood glucose, anorexia, dehydration, diabetes mellitus, bursitis, collagen-vascular disease, costochondritis, joint disorder, and muscle cramps.

Understand Your Risk for Side Effects with the Rxight® PGx Testing Program

Inter-patient variability in metabolism of Rythmol may explain why some patients develop severe side effects while others do not have any problems when taking the medication. MD Labs offers the most comprehensive CLIA-certified PGx testing program, Rxight®. The Rxight® panel covers over two hundred prescription and over-the-counter (OTC) medications across 50 clinically significant medication classes, including antiarrhythmic medications. Variants (polymorphisms) on 18 different genes are analyzed in the panel. The testing is designed to identify your genetic variations that impact medication metabolism, and thus reduce the chances of developing side effects or not deriving therapeutic benefit. A simple DNA cheek swab is all that is required, and it can be performed at any pharmacy participating in the Rxight® program.

How Does Pharmacogenetic Testing Work?

Identifying inter-individual genetic variations in the metabolism of medications is the foundation of the relatively new field of pharmacogenetics, and it can aid in doctors decision making when prescribing pharmacological agents. For instance, identifying a patient as a poor metabolizer may result in a lower dose being prescribed. This may reduce the probability of that patient developing adverse effects.

Some patients suffer no adverse reactions while taking medications such as Rythmol, while others may suffer life-threatening side effects. This interpatient variability is partly due to individual genetic differences. Propafenone is metabolized by a number of liver enzymes. Polymorphisms in a primary liver enzyme have been shown to increase the probability of developing adverse effects when taking the medication. So-called “poor metabolizers” were shown to have more adverse effects than extensive (rapid) metabolizers, and with PGx testing, these side effects can be mitigated by finding a safer, lower dose or alternative medication – preferably before treatment even begins.


Contributors to this Article:
Michael Sapko, MD, PhD; Deborah Kallick, PhD, Medicinal Chemistry

Read more about Rxight® pharmacogenetics