How does this medication work? What will it do for me?

Mexiletine belongs to the class of medications called antiarrhythmics. It is used to treat certain types of abnormal heart rhythms. It works by affecting nerve signals in the cells of the heart, which helps the heart beat more regularly.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

What form(s) does this medication come in?

200 mg
Each hard gelatin capsule with opaque orange cap and opaque orange body, filled with white powder, and imprinted with "A28" on the cap and "200" on the body in black ink, contains 200 mg of mexiletine hydrochloride. Nonmedicinal ingredients: colloidal silicon dioxide, magnesium stearate, and pregelatinized starch; capsule shell: FD&C Yellow 6, gelatin, purified water, and titanium dioxide; imprinting ink: black iron oxide, butyl alcohol, dehydrated alcohol, isopropyl alcohol, propylene glycol, potassium hydroxide, purified water, shellac, and strong ammonia solution.

How should I use this medication?

The usual starting dose of mexiletine is 200 mg 3 times daily. The dose can be increased to a maximum of 1,200 mg daily, given in 3 or 4 divided doses. Most people will respond at a daily dose of 600 mg to 900 mg. The dose varies depending on the person's needs and the way they respond to and tolerate the medication.

Mexiletine should be taken with plenty of liquid, food, or an antacid.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from moisture, and keep it out of the reach of children.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

Who should NOT take this medication?

Do not use this medication if you:

  • are allergic to mexiletine or any ingredients of the medication
  • are allergic to amide anaesthetics
  • have cardiogenic shock
  • have second- or third-degree heart block (without a pacemaker)

What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • appetite changes
  • changed sleep habits
  • changed interest in sexual activity
  • constipation
  • diarrhea
  • dry mouth
  • dry skin
  • fatigue
  • hair loss
  • headache
  • heartburn
  • lightheadedness
  • nausea
  • nervousness
  • rash
  • unusual prickling or burning sensations
  • vomiting
  • weakness

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • abdominal pain
  • changes in thoughts or behaviour
  • chest pain
  • confusion
  • coordination problems
  • excessive sweating
  • fainting
  • hallucinations (e.g., seeing or hearing things that aren’t there)
  • new abnormal heart rhythms (fast, slow, or pounding heartbeat)
  • shortness of breath
  • signs of clotting problems (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don’t stop bleeding)
  • signs of kidney failure (e.g., confusion, itchiness or rash, puffiness in face and hands, decreased urine production, swelling, fatigue, weight gain)
  • signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
  • symptoms of angina (e.g., chest pain or pressure, discomfort in the shoulder, arm, back, throat, jaw, or teeth)
  • symptoms of depression (e.g., loss of interest in activities, appetite changes, sleep changes, feeling hopeless)
  • symptoms of heart failure (e.g., shortness of breath, swelling of the hands and feet, fatigue, cough, lack of appetite, decreased ability to exercise, rapid or irregular heartbeat)
  • symptoms of infection (e.g., fatigue, fever, aches, flu-like symptoms)
  • symptoms of high blood pressure: (e.g., chest pain, blurred vision, dizziness, excessive tiredness, headache, stronger or faster heartbeat)
  • symptoms of low blood pressure (e.g., fainting, dizziness, lightheadedness, blurred vision, increased thirst, nausea)
  • trouble swallowing
  • trembling
  • vision changes

Stop taking the medication and seek immediate medical attention if any of the following occur:

  • seizures
  • signs of a severe allergic reaction (e.g., hives, peeling or blistering skin, difficulty breathing, swelling of the mouth or throat)
  • signs of a severe skin reaction (e.g., blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort)
  • symptoms of heart failure (e.g., shortness of breath, fast breathing or heartbeat, pale skin, sweating, loss of consciousness, swelling of the hands and feet)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Abnormal heart rhythms: Certain medications used to treat abnormal heart rhythms, including mexiletine, may cause new abnormal heart rhythms or worsen existing ones. Your doctor will monitor you closely while you are taking mexiletine. If you experience a fast, slow, or irregular heartbeat; fainting; heart palpitations; or dizziness while taking this medication, contact your doctor immediately.

Blood clotting: This medication can reduce the number of platelet cells in the blood. Platelets help the blood to clot, and a shortage could make you bleed more easily. Tell your doctor about any signs that your blood is not clotting as quickly as usual. Such symptoms may include black and tarry stools, blood in the urine, easy bruising, or cuts that won't stop bleeding.

Dizziness, tremor, and coordination: This medication may cause dizziness, tremor, or changes in coordination. Do not drive or operate machinery until you know how this medication affects you.

Drug Reactions with Eosinophilia and Systemic Symptoms (DRESS): DRESS is a type of allergic reaction that can affect multiple organs. Early symptoms often include fever, rash on the face or upper body, and swelling of the face. In severe cases, organs such as the kidney or liver can become inflamed and function decreases. If you experience unusual symptoms, contact your doctor as soon as possible.

Heart failure: Mexiletine can cause or worsen heart failure. If you have heart failure and are taking this medication, your doctor will monitor you closely during treatment. If you notice shortness of breath; weight gain; or swelling in the hands, feet, or lower legs while taking mexiletine, contact your doctor immediately.

Infection: This medication can reduce the number of cells that fight infection in the body (white blood cells). If possible, avoid contact with people who have contagious infections. Tell your doctor immediately if you begin to notice the signs of an infection such as fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness. Your doctor will do blood tests regularly to monitor the number of specific types of blood cells in your blood.

Liver problems: Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. Mexiletine can cause liver problems. Your doctor will monitor your liver function while you are taking this medication. If you experience nausea, abdominal pain, yellowing of the skin or eyes, pale stools, or dark urine while taking mexiletine, contact your doctor immediately. People with liver problems should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Low blood pressure: Mexiletine may cause or worsen low blood pressure. Tell your doctor if you experience symptoms of severely decreased blood pressure, such as weakness or dizziness, particularly when rising suddenly from a sitting or lying position. If you have low blood pressure, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Seizures: People with a history of seizures should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are breast-feeding and taking mexiletine, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children.

What other drugs could interact with this medication?

For a full list of interactions, use the Drug Interaction Checker available on the website.

If you are taking other medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

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