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Oral Antiarrhythmics



An arrhythmia is a problem with the rate or rhythm of the heartbeat. It is a common heart disease which occurs when the electrical impulses in your heart do not coordinate the heartbeats properly, causing your heart to beat too fast (tachycardia), too slow (bradycardia) or irregularly.

Most arrhythmias are harmless, but some can be serious or even life threatening. Arrhythmias may not cause any signs or symptoms. Your doctor may find you have an arrhythmia during routine body check without noticeable symptoms. However, noticeable symptoms of arrhythmia may include palpitations or rapid thumping in your chest, light-headedness, syncope, fatigue, shortness of breath, chest pain and decrease in exercise tolerance. In severe situations, you may have symptoms of slurred speech, visual disturbance and limb weakness suggesting stroke, etc. Moreover, arrhythmia causes a five-fold increase in stroke, three-fold increase in heart failure and two-fold increase in death.

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Treatment used

Treatment depends on the type and severity of arrhythmia you have. Some mild arrhythmias do not need to be treated, while other arrhythmias can be treated with medical procedures (e.g. artificial pacemaker), surgery (e.g. coronary artery bypass grafting if the arrhythmia is caused by coronary heart disease) and antiarrhythmic drugs. Your doctor will find out the underlying cause for your arrhythmia and decide what kind of treatment should be used.

Antiarrhythmics are the medicines which slow down a heart that's beating too fast. These medicines can also change an abnormal heart rhythm to a normal, steady rhythm. However, no medicine can reliably speed up your heart if you have bradycardia (pacemaker may be used in such case).

All antiarrhythmics are prescription-only medicines and should only be used under close supervision by healthcare professionals. They are available in many dosage forms such as tablets, capsules, and injections.


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Classes of oral antiarrhythmics

In general, antiarrhythmics could be divided into four main classes: I to IV.

Class I is the drugs that block the fast inward sodium channels and therefore interfere with depolarization. They have both antiarrhythmic and local anaesthetic effect. Flecainide is one of the examples.

Class II drugs are characterised by beta-blocking property. They act by reducing both heart rate and myocardial contractility, and also slowing conduction of impulses through the myocardial conducting system. Examples include beta blockers such as atenolol, metoprolol and propranolol (but sotalol, one of the beta blockers, presents mainly class III activity).

Class III drugs block the potassium channels, thus slowing the repolarisation phase and prolonging the action potential duration and the QT interval. Examples include amiodarone and sotalol.

Class IV drugs are some of the calcium-channel blockers (but not dihydropyridine calcium-channel blockers), such as diltiazem and verapamil which act by blocking the slow inward calcium channels and particularly affect the pacemaker cells.

Digoxin, a commonly used drug for arrhythmia, does not fit into the above-mentioned classification. Digoxin can increase the force of myocardial contraction and reduce the conductivity of the heart. It also has a direct action on vascular smooth muscle and indirect effects mediated mainly by the autonomic nervous system, and particularly by an increase in vagal activity.

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Common side effects and precautions

Drug class
Common side effects
1. Flecainide
  • Dizziness
  • Visual disturbances
  • Lightheadedness
  • Nausea and vomiting
  • Headache
  • Edema
  • Asthenia
  • Fatigue
  • Gastro-intestinal disturbances
  • Tremor
  • Use with caution in patients with pacemakers; atrial fibrillation following heart surgery.
  • Use with caution in elderly
  • Treatment should be started in hospital or under specialist supervision
  • Should only be used in serious or life-threatening arrhythmias
  • Before starting treatment, electrolyte imbalances should be corrected
  • Dosage should be reduced in patients with renal impairment
  • Should not be used in patients with heart failure, abnormal left ventricular function, history of myocardial infarction, haemodynamically significant valvular heart disease, sinus node dysfunction, long-standing atrial fibrillation where conversion to sinus rhythm not attempted, atrial conduction defects, second-degree or greater AV block and hepatic impairment
2.Beta blockers (e.g. atenolol, metoprolol, propranolol, sotalol)
  • Fatigue
  • Coldness of the extremities
  • Gastro-intestinal disturbances
  • Nausea and vomiting
  • Bradycardia
  • Hypotension
  • Bronchospasm
  • Dyspnoea
  • Headache
  • Dizziness
  • Sleep disturbances
  • Nightmare
  • Avoid abrupt withdrawal especially in ischaemic heart disease
  • Use with caution in patients with first-degree AV block, portal hypertension, diabetes, history of obstructive airways disease and myasthenia gravis
  • Symptoms of hypoglycaemia and hyperthyroidism may be masked
  • Should not be used in patients with asthma, uncontrolled heart failure, hypotension, marked bradycardia, Prinzmetal's angina, metabolic acidosis, cardiogenic shock, severe peripheral arterial disease, sinus bradycardia, phaeochromocytoma, and second- or third-degree AV block
  • Psoriasis may be aggravated
  • Dosage should be reduced in patients with renal and hepatic impairment
3. Amiodarone
  • Nausea and vomiting
  • Taste disturbances
  • Raised serum transaminases
  • Jaundice
  • Bradycardia
  • Pulmonary toxicity
  • Tremor
  • Headache
  • Sleep disorders
  • Hypothyroidism
  • Hyperthyroidism
  • Skin discoloration
  • Thyroid, liver and pulmonary function should be monitored regularly
  • Electrolyte disorders should be corrected before starting treatment
  • Chest x-ray is required before starting treatment
  • Use with caution in patients with hypokalaemia, heart failure, acute porphyria
  • Should not be used in patients with bradycardia, sino-atrial block, AV block or other severe conduction disorders, severe hypotension, severe respiratory failure, thyroid dysfunction and iodine sensitivity
  • Avoid exposure to sunlight
4.Calcium channel blockers (e.g. diltiazem, verapamil)
  • Flushing
  • Headache
  • Fatigue
  • Ankle edema
  • Constipation
  • Dizziness
  • Gastro-intestinal disturbances
  • Nausea and vomiting
  • Bradycardia
  • Rashes
  • Use with caution in patients with first-degree AV block
  • Should not be used in patients with the sick sinus syndrome, second- or third-degree AV block, marked bradycardia, hypotension, heart failure or impaired left ventricular function and acute porphyria
  • Should not be used in combination with beta blockers
  • Dosage should be reduced in patients with renal (for diltiazem) and hepatic impairment (for both diltiazem and verapamil)
  • Avoid drinking large quantities of grapefruit juice
5. Digoxin
  • Nausea and vomiting
  • Diarrhoea
  • Dizziness
  • Blurred vision
  • Rash
  • Eosinophilia
  • Use with caution in patients with recent myocardial infarction, sick sinus syndrome, thyroid disease, severe respiratory disease, hypokalaemia, hypomagnesaemia, hypercalcaemia, and hypoxia
  • Dosage should be reduced in elderly and patient with renal impairment
  • Monitor serum electrolytes and renal function
  • Should not be used in second or third degree AV block, Wolff-Parkinson-White syndrome, ventricular tachycardia or fibrillation, myocarditis and constrictive pericarditis


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General advice on taking oral antiarrhythmics

  • Discuss with your doctor how to take your pulse and learn what pulse rate is normal for you.
  • If you feel dizzy, faint, pain in your chest, neck, jaw, arms, back or shoulders or shortness of breath, you should lie down and take a rest. Don't try to walk or drive. Ask for an ambulance immediately.
  • Lifestyle modification may help keep your heart healthy, such as eating heart-healthy food (e.g. fruits, vegetables, grains, fat-free dairy products, poultry without skin), increasing your physical activity moderately, quitting smoking, reducing the amount of stress, and avoiding stimulant medications (e.g. colds and nasal congestion medicines).
  • Antiarrhythmic drugs should only be purchased with a doctor’s prescription and taken as directed by your doctor.
  • Be familiar with the name and dosage of the antiarrhythmic drugs you are taking. Be cautious of their possible side effects.
  • Follow doctor’s advice on the use of your antiarrhythmic drugs. Do not stop or change the regimen by yourself.

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Communication with your doctor

  • Communicate with your doctor for the best treatment option. Your doctor will prescribe the most appropriate drugs for you after considering your condition and your response to the drugs.
  • Antiarrhythmic drugs can interact with other medicines. Inform your doctor of the medicines you are taking, including over-the-counter medicines, so they can decide whether an antiarrhythmic drug is safe for you to take.
  • Inform your doctor of any diseases you are suffering, as some diseases may warrant special precautionary measures.
  • Inform your doctor that you are pregnant or breast feeding as some of the antiarrhythmic drugs should not be taken by women who are pregnant or breast feeding.
  • Seek medical advice immediately if you experience any symptoms or side effects suspected to be related to antiarrhythmic drugs. Your doctor may review your type of medication.
  • Seek medical advice if your symptoms worsen or you have any concerns about the medicines you are taking.
  • Always ask your doctor before taking any other medicines or health products as they may affect the effect or increase the side effects of your medication.
  • Have regular medical follow-ups as advised by your doctor.

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Storage of oral antiarrhythmics

Oral antiarrhythmic drugs should be kept in a cool and dry place. Unless specified on the label, medicines should not be stored in refrigerators. Furthermore, drugs should be kept properly in places unreachable by children to prevent accidental ingestion.


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Acknowledgement: The Drug Office would like to thank the Professional Development and Quality Assurance (PD&QA) for their valuable contribution to the preparation of this article.

Drug Office
Department of Health
Oct 2014