Flecainide side effects and how to avoid them

Common flecainide side effects | Serious side effects | Irregular heartbeat | Heart failure | Increased risk of fatal heart attack |  Side effects timeline | Contraindications | Warnings | Interactions | How to avoid side effects | How to treat side effects

Flecainide is a generic prescription drug used to treat or prevent serious and life-threatening heartbeat abnormalities. These abnormalities include chaotic, fast heartbeats of the upper chambers of the heart (paroxysmal atrial fibrillation and atrial flutter) and fast or irregular heartbeats of the lower chambers (ventricular tachycardia and other ventricular arrhythmias). As an antiarrhythmic, flecainide slows and stabilizes heartbeats by weakening nerve activity. 

Although it is an effective drug, flecainide can cause side effects, some of which can be severe. Because of the possibility of severe side effects on the heart, flecainide should only be reserved for serious heart rhythm problems. 

Common side effects of flecainide

Flecainide can cause various side effects, including side effects on the heart, lungs, and digestive system. Consult a healthcare provider if you experience any side effects or if side effects persist or worsen. The most common side effects of flecainide include:

• Dizziness, lightheadedness, feeling faint, or unsteadiness
• Visual impairment, such as blurred vision and seeing spots
• Trouble breathing
• Headache
• Nausea
• Fatigue
• Palpitations
• Chest pain
• Weakness
• Tremor
• Constipation
• Fluid retention and swelling
• Abdominal pain

Serious side effects of flecainide

Some of the most serious side effects of flecainide include:

• New or worsened arrhythmias
• Heart block
• Heart failure
• Cardiac arrest
• Liver problems, such as liver damage or liver failure
• Low blood cell counts
• Lung problems
• Allergic reactions

Flecainide and irregular heartbeats

One important thing to know is that flecainide, an antiarrhythmic, can have proarrhythmic effects. That is, flecainide can cause arrhythmias or irregular heartbeats even though it’s prescribed to treat irregular heartbeats. In some people, the drug may cause worsened or new irregular heartbeats, which can be life-threatening. Heart rhythm changes can include PR, QRS, and QT prolongation. 

The incidence of new or worsened arrhythmias in clinical trials ranges from 1% to 7% of patients, depending on the underlying condition being treated. About 80% of heart rhythm problems occur in the first two weeks of treatment for a certain type of ventricular arrhythmia. To prevent serious problems, healthcare professionals typically start flecainide treatment in a hospital where they can monitor the heart and intervene if there’s trouble. People who take flecainide at home are recommended to keep up with regular office visits to monitor heart rate and heart rhythm. 

Flecainide and heart failure

The use of flecainide also carries a risk of new or worsened heart failure, a condition in which the heart cannot pump enough blood to the body. Heart failure is not uncommon in people with arrhythmias. In clinical trials, the incidence of new or worsened heart failure ranges from 0.4% to 26% of participants, depending on the heart condition being treated and whether the patient has pre-existing heart failure. It is important for people taking flecainide to be familiar with the symptoms of heart failure and immediately report them to the prescriber or other healthcare professional.

Increased risk of death after a heart attack

According to results from the National Heart Lung and Blood Institute’s Cardiac Arrhythmia Suppression Trial (CAST), the use of flecainide may cause an increased risk of death or cardiac arrest in certain patients. An increased risk of death was observed in patients who experienced a recent heart attack. Consult a healthcare provider for appropriate treatment options before taking flecainide after a recent heart attack. 

How soon do flecainide side effects start?

Flecainide begins affecting the heart after the very first dose. Many of flecainide’s most common side effects, such as dizziness, headache, fatigue, stomach pain, and tremor, occur early in treatment. Heart rhythm problems have mostly occurred during the first two weeks of treatment for sustained ventricular tachycardia. However, rapid or slow heartbeats may occur after taking the first dose. Other serious side effects, including liver problems, lung problems, and blood cell problems, may develop within a few days, a few weeks, or longer.

How long do flecainide side effects last?

Mild side effects generally subside over time as the body gets used to the medication. Those that don’t typically resolve once the medicine is stopped. However, flecainide is often taken with other heart medicines. Some of the problems caused by flecainide may persist while continuing or switching to similar medications. Heart problems may require that flecainide be stopped.

What are the long-term side effects of flecainide?

Flecainide treatment is usually long-term and can last for months. While flecainide is not linked to serious long-term side effects, worsening heart failure symptoms, for example, may be more likely to develop in people with pre-existing heart failure. Some clinical studies have suggested that long-term use may cause various types of lung diseases, including inflammation in the lungs (pneumonitis) and scarring (fibrosis). However, other clinical studies have found that lung problems can start early in flecainide treatment.

Flecainide contraindications

Flecainide should be avoided in people with:

• Second- or third-degree heart block (also known as AV block)
• Right bundle branch block when associated with left hemiblock (bifascicular block) except in people with a pacemaker
• Cardiogenic shock (an acute, life-threatening condition in which the heart is unable to pump enough blood to the body)
• A known allergic reaction to flecainide

Pregnancy

Flecainide is only used during pregnancy if the benefits outweigh the risks. Flecainide has been shown to cause birth defects in animal studies, but there are no sufficient studies on the use of flecainide in pregnant women. It is not known if flecainide affects newborns if taken near the end of pregnancy.

Breastfeeding

Flecainide has been shown to pass into human breast milk. Nursing infants may receive a small dose. Studies suggest that there is a low risk of side effects in a nursing infant, especially if it is older than two months.

Children

The FDA has approved flecainide as safe and effective for use in children and infants. Because of potential problems, it is recommended that flecainide be started in the hospital under the supervision of a cardiologist who has expertise in child arrhythmias.

Seniors

Flecainide can be used safely in older adults. However, because people older than 65 are more likely to have liver or kidney problems than other people, the risk of adverse effects may be higher in elderly adults. Close monitoring may be required in seniors taking flecainide.

Flecainide warnings

The label of flecainide highlights several warnings, including those of proarrhythmic effects. It is important to take flecainide only as prescribed at the appropriate dosage determined by a healthcare provider. Close supervision and monitoring are generally recommended to avoid serious problems with flecainide. 

Black box warning

The FDA adds black box warnings to a drug if there is a high risk of serious problems. Black box warnings are not severe enough to ban the drug but severe enough to warn healthcare providers and patients about potential problems. Flecainide carries a warning about possible side effects on the heart:

• Flecainide may increase the risk of death or nonfatal cardiac arrest in people who have had a heart attack within two years of the start of flecainide treatment.
• Because of its proarrhythmic effects, flecainide is only appropriate for life-threatening heart rhythm problems. It should be avoided in people with chronic atrial fibrillation. 

Cautions

Because flecainide can cause serious heart problems, pre-existing heart conditions may be worsened by the drug. In these cases, extra caution and monitoring may be required. Patients with the following conditions should consult their healthcare provider before taking flecainide:

• Structural heart disease (such as heart valve defects or heart muscle disease)
• Congestive heart failure
• QT prolongation
• Electrolyte disturbances
• An implanted pacemaker
• Liver or kidney problems

Electrolyte imbalances can increase the risk of heartbeat abnormalities. In particular, low potassium or low magnesium must be corrected before flecainide can be safely taken.

People with liver dysfunction or moderate to severe kidney disease may need reduced doses. Otherwise, the drug could build up in the body, causing an increased risk of side effects.

Abuse and dependence

Flecainide is not linked to physical dependence, nor is it associated with drug abuse or misuse. 

Overdose

Call a poison control center or seek medical help if too much flecainide is taken. The maximum daily dosage is 300 mg per day for patients with paroxysmal supraventricular arrhythmias and 400 mg per day for patients with sustained ventricular tachycardia. The most appropriate dosage will depend on the condition being treated. In general, the lowest effective dose is recommended to prevent side effects. 

The most common symptoms of a flecainide overdose are nausea, vomiting, low blood pressure (hypotension), slow heartbeat (bradycardia), fainting (syncope), convulsions, and heart rhythm changes. Severe and even life-threatening heart rhythm problems and heart attacks are possible after an overdose.

Flecainide interactions

Flecainide should be used with caution with certain drugs. Some drug combinations involving flecainide should be avoided entirely. Consult a healthcare provider if you are taking other medications, including prescription drugs, over-the-counter medicine, or herbal supplements, before taking flecainide. Drugs that interact with flecainide include:

• Other antiarrhythmic drugs, such as amiodarone and quinidine
• Certain antipsychotic medications, such as thioridazine and pimozide
• Beta blockers, such as sotalol and propranolol 
• Calcium channel blockers, such as verapamil
• Cardiac glycosides, such as digoxin
• Certain antibiotics, such as clarithromycin and erythromycin
• Certain antifungals, such as fluconazole and voriconazole
• Selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine, paroxetine, and citalopram
• Certain anticonvulsants, such as phenytoin, phenobarbital, and carbamazepine
• Certain antiviral drugs, such as ritonavir and saquinavir
• Certain stomach acid reducers, such as cimetidine

Other drug interactions are possible, as this is not a complete list. Talk to your healthcare provider about other possible drug interactions. Your healthcare provider may recommend adjusting doses or monitoring for increased side effects when taking specific medications with flecainide. 

How to avoid flecainide side effects

Flecainide is generally reserved for serious heart problems because of the risk of serious side effects. For some people, the risks of taking flecainide outweigh its benefits. However, for many people, the side effects of flecainide are avoidable with the right guidance. 

1. Follow all instructions 

The most important rule is to use flecainide as directed. Your prescriber will advise you on how much to take and when to take each dose of flecainide. Your healthcare provider may also provide other instructions to ensure the drug is taken safely and effectively. Always consult your healthcare provider if you have any concerns about taking the medication correctly.

2. Set dose reminders

Missing a dose or taking too much flecainide can be a problem. Ask your pharmacist for tools that can help you keep track of the dosing schedule. These tools may include diaries, calendars, smartphone apps, or pill-bottle alarms. 

3. Don’t take a double dose

The risk of possible side effects, including serious ones, is higher if too much medicine is taken. Don’t take a double dose to make up for a missed dose. If you miss a dose, you can take it when you remember. However, if it’s almost time for the next dose, skip the missed dose. Keep to the schedule and take the next dose when it’s due.

4. Get support from a loved one

If you have trouble taking or remembering to take your medicine, ask a family member or friend for support. They may be able to help remind you when and how to take your medication.

5. Tell the prescriber about all medical conditions you have

Before you start treatment, you should tell your healthcare provider your complete medical history. In most cases, flecainide will be prescribed by a cardiologist who is skilled in treating arrhythmias and has ordered any necessary tests, such as an electrocardiogram (ECG). You should tell your healthcare provider about any pre-existing medical conditions you have, such as:

• Heart rhythm problems
• Chronic atrial fibrillation
• A heart attack in the last two years
• Heart failure
• Electrolyte imbalances
• Liver disease
• Pregnancy or any plans to become pregnant
• Breastfeeding or plans to breastfeed

6. Tell the prescriber about other medication you take

Drug interactions are another source of flecainide adverse effects, so the prescriber should have a complete picture of all the prescription drugs, over-the-counter medicines, and dietary supplements that you take. Some medications or doses may need to be changed or adjusted.

8. Don’t skip follow-up visits

Regular ECGs, blood tests, or other monitoring tests are often necessary to make sure flecainide is working and not causing any problems. Stick with your follow-up appointments with your doctor to ensure you’re taking the medication safely and correctly. 

9. Don’t stop taking flecainide

Don’t stop taking flecainide unless told to do so by your healthcare provider. 

How to treat side effects of flecainide

Minor side effects usually resolve on their own, but it is important that the prescriber knows about any side effects you experience when taking flecainide. Even though a side effect may seem trivial, it might be a sign of a more serious problem. Report any side effects you’ve experienced at each follow-up visit. If you experience persistent or serious side effects, contact the prescriber immediately or get emergency medical help.

Dizziness or lightheadedness

If you feel dizzy or unsteady, you can sit down until it stops. Stand up slowly when the spinning stops. You can report dizziness or feeling faint to the prescriber, especially if it comes on suddenly or doesn’t seem to go away.

Heart problems

Contact the prescriber immediately or get emergency medical help if you experience a fast, pounding heartbeat (palpitations), slow heartbeat, chest pain, sudden or unexplained dizziness, weak pulse, or shortness of breath.

Heart failure

New or worsening heart failure symptoms can develop while taking flecainide. You should tell your healthcare provider about any symptoms of heart failure you experience. The most prominent symptoms of heart failure are swelling in the arms or legs, rapid weight gain, and trouble breathing. Symptoms of heart failure can appear within a few hours to a few months after starting treatment.

Liver dysfunction

Contact your healthcare provider if you experience signs or symptoms of liver problems, such as:

• Upper right abdominal pain
• Dark-colored urine
• Yellowing of the skin or eyes 

Sources

• Drug-induced acute pneumonitis following initiation of flecainide therapy after pulmonary vein isolation ablation in a patient with mitral stenosis and previous chronic amiodarone use, Heart Rhythm Case Reports
• Flecainide, Epocrates
• Flecainide, Drugs and Lactation Database
• Flecainide, StatPearls
• Flecainide drug summary, Prescriber’s Digital Reference
• Flecainide acetate tablet prescribing information, U.S. National Library of Medicine