Medication Information Leaflet

What is this medication for?

Quinidine is used in the treatment of abnormal heart rhythm. It works by correcting irregular heartbeats so that the heart works properly to pump blood

How should I take/use this medication?

  • Do not stop taking your medication without checking with your healthcare professional
  • You may take this medication with or without food

What should I do if I forget to take/use this medication?

If you forget to take a dose, take it as soon as you remember. Then take your next dose at the usual time. Do not take two doses to make up for the missed dose

What precautions should I take?

Inform your healthcare professional if:

  • You are allergic to this medication or any of the other ingredients of this medication
  • You are pregnant, planning to become pregnant, or breastfeeding
  • You are taking any other medications, including supplements, traditional medications and herbal remedies
  • You have liver or kidney problems
  • You have an abnormal heart condition known as acquired QT interval prolongation
  • You have any heart problems other than your abnormal heart rhythm, such as heart failure, or a history of a heart attack.
  • You have a condition known as myasthenia gravis (a type of illness characterised by muscle weakness)
  • You have a condition known as Glucose-6 Phosphate Dehydrogenase (G6PD) deficiency, a genetic condition in which your red blood cells break down faster than they are made

What are some common side-effects of this medication?

  • Dizziness and headaches
    • Getting up slowly or changing posture slowly may help. Take a rest by sitting or lying down if you feel dizzy
  • Nausea, vomiting, diarrhea
  • Stomach pain or heartburn

What are some rare but serious side-effects that I need to seek medical advice immediately?

Quinidine may slow down your heartbeat and worsen existing abnormal heart rhythm. Symptoms of an abnormal heart rhythm includes:

  • Irregular heartbeat e.g. slowed heartbeat or palpitations
  • Severe dizziness or fainting spells

Quinidine may cause a condition known as thrombocytopenia, where the platelet count in the blood is below normal. Symptoms of this condition may include unexplained bruising or bleeding.

Very rarely at normal doses, Quinidine may lead to a group of symptoms (known as cinchonism): ringing in the ears or impaired hearing, blurring of vision or mental confusion.

Lastly, the symptoms of a drug allergy include one or more of the following:

  • Swollen face/eyes/lips/tongue
  • Difficulty in breathing
  • Itchy skin rashes over your whole body

If you experience any of these symptoms, you should stop your medication and see your healthcare professional immediately

What food or medication should I avoid when I take this medication?

Avoid taking grapefruit and grapefruit juice when you are taking this medication as these may interact with your medication and increase the risk of side-effects.

Avoid making drastic changes in the amount of salt in your diet as this might change the level of quinidine in your blood

Some medications may interact with Quinidine and affect their effectiveness or increase the risk of side effects. Inform your healthcare professional of other medications you are currently taking. Some examples include medications for treating the below conditions:

  • Bacterial infections (eg clarithromycin, erythromycin, levofloxacin)
  • Fungal infections (eg ketoconazole, itraconazole)
  • Viral infection (eg ritonavir)

How should I store this medication?

Store in a cool and dry place, away from direct sunlight. Keep this medication away from children.

How should I throw away this medication safely?

Pack this medication into a black trash bag and seal it tightly before throwing it into the rubbish chute or bin.


Please take note that the above is not a complete list of all possible side effects. If you have any concerns about your medication or if you have other side effects that you think are caused by this medication, please consult your doctor or pharmacist.

If you take more than the recommended dose, please seek medical advice immediately. The information provided on this page does not replace information from your healthcare professional. Please consult your healthcare professional for more information.

This article is jointly developed by members of the National Medication Information workgroup. The workgroup consists of cluster partners (National Healthcare Group, National University Health System and SingHealth), community pharmacies (Guardian, Unity and Watsons) and Pharmaceutical Society of Singapore. The content does not reflect drug availability and supply information in pharmacies and healthcare institutions. You are advised to check with the respective institutions for such information.

Last updated on May 2023

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