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Generic name: flecainideFLEK-a-nide ]
Drug class: Group I antiarrhythmics

Medically reviewed by on Aug 4, 2023. Written by Cerner Multum.

What is Tambocor?

Tambocor is a Class IC anti-arrhythmic that is used in certain situations to prevent serious heart rhythm disorders.

Tambocor may also be used for purposes not listed in this medication guide.

Tambocor side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Tambocor may cause serious side effects. Call your doctor at once if you have:

  • fast or pounding heartbeats;

  • fluttering in your chest, shortness of breath, and sudden dizziness (like you might pass out);

  • slow heart rate, weak pulse, slow breathing (breathing may stop);

  • feeling short of breath;

  • swelling, rapid weight gain;

  • pale skin, easy bruising or bleeding, unusual weakness;

  • fever, flu-like symptoms; or

  • jaundice (yellowing of the skin or eyes).

Common side effects of Tambocor may include:

  • dizziness;

  • vision problems;

  • trouble breathing;

  • headache;

  • nausea; or

  • feeling weak or tired.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


You should not use Tambocor if you have a serious heart condition such as bundle branch block or AV block (without a pacemaker), or if your heart cannot pump blood properly.

You may receive your first dose in a hospital or clinic setting to quickly treat any serious side effects.

Before taking this medicine

You should not use Tambocor if you are allergic to it, or if:

  • you have a serious heart condition such as bundle branch block or AV block (unless you have a pacemaker); or

  • your heart cannot pump blood properly.

Tell your doctor if you have ever had:

It is not known whether this medicine will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

It may not be safe to breast-feed while using this medicine. Ask your doctor about any risk.

How should I take Tambocor?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.

You may receive your first few doses in a hospital or clinic setting to quickly treat any serious side effects.

Your heart rate will be monitored using an electrocardiograph or ECG (sometimes called an EKG). This will help your doctor determine how long to treat you with Tambocor.

You may also need frequent blood tests to check your liver or kidney function.

Store at room temperature away from moisture, heat, and light.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include nausea, vomiting, slow heart rate, fainting, or seizure (convulsions).

What should I avoid while taking Tambocor?

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

What other drugs will affect Tambocor?

Tell your doctor about all your other medicines, especially:

This list is not complete. Other drugs may affect Tambocor, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.