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.

Your doctor may have suggested this medication for conditions other than the ones listed in these drug information articles. As well, some forms of this medication may not be used for all of the conditions discussed here. 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?

100 mg
Each opaque, scarlet cap and opaque-orange body, hard gelatin capsule, with "N" and "100" imprinted on opposing cap and body portions of the capsule, contains mexiletine HCl 100 mg. Nonmedicinal ingredients: colloidal silicon dioxide, D&C Red No. 33, FD&C Blue No. 1, FD&C Red No. 3, FD&C Red No. 40, gelatin, magnesium stearate, parabens, pregelatinized starch, silicon dioxide, sodium lauryl sulfate, talc, titanium dioxide, and Yellow No. 6. Gluten- and tartrazine-free.

200 mg
Each scarlet, hard gelatin capsule, with "N" and "200" imprinted on opposing cap and body portions of the capsule, contains mexiletine HCl 200 mg. Nonmedicinal ingredients: colloidal silicon dioxide, D&C Red No. 33, FD&C Blue No. 1, FD&C Red No. 40, gelatin, magnesium stearate, parabens, pregelatinized starch, silicon dioxide, sodium lauryl sulfate, talc, and titanium dioxide. Gluten- and tartrazine-free.

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 divided doses. Most people will respond at a daily dose of 400 mg to 800 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?

Mexiletine should not be used by anyone who:

  • is allergic to mexiletine or to any of the ingredients of the medication
  • has a low heart rate
  • has cardiogenic shock
  • has 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.

  • constipation
  • diarrhea
  • dry mouth
  • fatigue
  • headache
  • heartburn
  • nausea
  • nervousness
  • rash
  • trouble sleeping
  • 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 check with your doctor or seek medical attention.

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

  • changes in thoughts or behaviour
  • chest pain
  • confusion
  • coordination problems
  • lightheadedness
  • new abnormal heart rhythms (fast, pounding heartbeat)
  • "ringing in the ears"
  • shortness of breath, swelling of the hands and feet
  • symptoms of depression (e.g., loss of interest in activities, appetite changes, sleep changes, feeling hopeless)
  • 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)

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 your 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 of any signs that your blood is not clotting as quickly. 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.

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: 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 worsen low blood pressure. People with low blood pressure 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.

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 a breast-feeding mother and are 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?

There may be an interaction between mexiletine and any of the following:

  • acetazolamide
  • ammonium chloride
  • bromazepine
  • bupropion
  • caffeine
  • clozapine
  • clomipramine
  • cyclobenzaprine
  • dacarbazine
  • delavirdine
  • flutamide
  • ketoconazole
  • lidocaine
  • narcotic medications
  • olanzepine
  • other medications used to treat abnormal heart rhythms (e.g., quinidine, procainamide, disopyramide)
  • phenytoin
  • pimozide
  • quinolone antibiotics (e.g., ciprofloxacin, norfloxacin, ofloxacin)
  • rifampin
  • ritonavir
  • selective serotonin reuptake inhibitors (SSRIs; e.g., fluvoxamine, fluoxetine, paroxetine, citalopram, escitalopram)
  • sodium bicarbonate
  • terbinafine
  • theophylline
  • thioridazine

If you are taking any of these 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.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that 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.