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Side Effects of


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Antiarrhythmic medications are a class used in the treatment of abnormal heart rhythms (e.g., atrial flutter, ventricular tachycardia, ventricular fibrillation, etc.).

Antiarrhythmic medications are split into 5 broad classes. These are detailed below:

  • Class I – These agents block sodium channels. Class I is made up of 3 sub classes (1a, 1b, 1c). The class includes drugs like propafenone, lidocaine and quinidine. They are used to treat an array of ventricular arrhythmias.
  • Class II – These block sympathetic nervous system action. They are usually beat blockers like propranolol or timolol. They prevent recurrence of tachyarrhythmias and myocardial infarction.
  • Class III – These drugs block potassium channels such as amiodarone.
  • Class IV – These block calcium channels and include drugs such as verapamil.
  • Class V – These agents work by unknown mechanisms, e.g., adenosine or digoxin.

Antiarrhythmic Drug Side Effects by Class

Class Ia agents like quinidine are used for ventricular arrhythmias. They are associated with some of the following common side effects:

  • Rash (drug eruption)
  • Abdominal Pain
  • Nausea
  • Vomiting
  • Diarrhea
  • Hemoptysis (coughing up blood)
  • Tinnitus
  • Hypoglycemia (low blood sugar)

Class Ib drugs like lidocaine are associated with the following side effects (side effects may vary between sub class and drug):

  • Restlessness
  • Agitation
  • Dizziness
  • Cardiovascular side effects
  • Seizure
  • Nausea
  • Vomiting
  • Psychosis

Class Ic drugs like flecainide can be used to prevent paroxysmal atrial fibrillation. Side effects include:

  • Prolongation of the PR QRS and QT intervals
  • Exacerbation of congestive heart failure
  • Exacerbation of myasthenia gravis
  • Nausea
  • Constipation
  • Pain
  • Impotence
  • Psychosis

Class II drugs like propranolol are also associated with a number of side effects. These include:

  • Hypotension (low blood pressure)
  • Cold extremities
  • Raynaud’s syndrome (can result in cold extremities)
  • Fatigue
  • Sleep disturbances
  • Nightmares
  • Sleep disorder
  • Agitation
  • Somnolence (lack of energy)
  • Irritability
  • Dizziness
  • Paresthesia (pins and needles)
  • Seizures
  • Renal insufficiency (inadequate blood perfusion of the kidneys)
  • Dyspnea (difficulty breathing)
  • Bronchospasm (fasciculations of the bronchus)
  • Hypoglycaemia (low blood glucose levels)
  • Anorexia
  • Nausea
  • Vomiting
  • Diarrhea
  • Abdominal pain
  • Flatulence (excessive gas)
  • Decreased appetite

Class III drugs like amiodarone are associated with the following side effects:

  • Hypotension
  • Bradycardia (low blood pressure)
  • Arrhythmia
  • Adult respiratory distress syndrome
  • Corneal microdeposits
  • Visual disturbance
  • Photosensitivity

Class IV drugs like verapamil are associated with the following side effects:

  • Headache
  • Dizziness
  • Lethargy
  • Hypotension (low blood pressure)
  • Edema (swelling)
  • Pharyngitis (sore throat)
  • Fatigue
  • Malaise
  • Pain
  • Rash
  • Scalp irritation
  • Sleep disturbance
  • Myalgia (muscle pain)
  • Allergic reactions
  • Hypersensitivity

Understand Your Risk for Side Effects with the Rxight® Genetic Test

Some patients will not suffer from adverse reactions when taking antiarrhythmic drugs. However, many patients will suffer multiple side effects. This inter-patient variability is partly accounted for by pharmacogenetic testing. Polymorphisms in the genes that code for enzymes and receptors that interact with antiarrhythmic can increase the probability of developing side effects. Getting a genetic test from MD Labs will let your prescribers and pharmacists understand the polymorphisms in the genes that cause the adverse reactions.

How Does Pharmacogenetic Testing Work?

For instance, most antiarrhythmic medications are metabolized by the cytochrome P450 superfamily of enzymes (the isoenzyme that is responsible will change between class and drug). Polymorphisms in these enzymes have been shown to increase the probability of developing side effects. Identifying these can then decrease the likelihood of suffering from adverse reactions from antiarrhytmics.

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

Antiarrhythmics Tested Include:

Read more about Rxight® Genetic Testing For Medication Effectiveness