Mexiletine 150mg Capsules
WARNING: This drug is only to be used to treat certain types of abnormal heartbeats that may be deadly. It may cause severe and sometimes deadly side effects. If you have questions, talk with the doctor.Rarely, liver problems have happened with this drug. Sometimes these problems happened within the first few weeks of taking it. Most of the time, they happened in people with heart failure or certain other heart problems. It is not known if this drug led to these cases of liver problems. If you have any questions, talk with the doctor. @ COMMON USES: It is used to treat certain types of abnormal heartbeats.This drug may need to be started in a hospital where you will be closely watched. Talk with your doctor.
Drug Class
Antiarrhythmic
Pharmacologic Class
Class IB Antiarrhythmic; Sodium Channel Blocker
Pregnancy Category
Category C
FDA Approved
Jan 1985
DEA Schedule
Not Controlled
Overview
What is this medicine?
Mexiletine is a medication used to treat certain types of irregular heartbeats, specifically those that start in the lower chambers of the heart (ventricles). It works by affecting the electrical signals in your heart to help it beat more regularly.
How to Use This Medicine
Taking Your Medication Correctly
To get the most benefit from your medication, take it exactly as directed by your doctor. Carefully read all the information provided with your prescription, and follow the instructions closely. It's recommended to take this medication with food or an antacid to help minimize potential stomach upset.
Continue taking your medication as prescribed by your doctor or healthcare provider, even if you start feeling better. This will help ensure that you receive the full benefits of the treatment.
Storing and Disposing of Your Medication
To maintain the effectiveness and safety of your medication, store it at room temperature, protected from light, and in a dry place. Avoid storing it in a bathroom, as the moisture and humidity can affect the medication's potency.
Keep all medications in a secure location, out of the reach of children and pets, to prevent accidental ingestion or exposure. When disposing of unused or expired medications, do not flush them down the toilet or pour them down the drain unless specifically instructed to do so by your pharmacist or healthcare provider.
Instead, check with your pharmacist for guidance on the best way to dispose of your medication. You may also want to inquire about drug take-back programs in your area, which can provide a safe and environmentally responsible way to dispose of unwanted medications.
What to Do If You Miss a Dose
If you miss a dose, take it as soon as you remember. However, if it's close to the time for your next scheduled dose, skip the missed dose and resume your regular dosing schedule. Do not take two doses at the same time or take extra doses, as this can increase the risk of side effects or other complications.
To get the most benefit from your medication, take it exactly as directed by your doctor. Carefully read all the information provided with your prescription, and follow the instructions closely. It's recommended to take this medication with food or an antacid to help minimize potential stomach upset.
Continue taking your medication as prescribed by your doctor or healthcare provider, even if you start feeling better. This will help ensure that you receive the full benefits of the treatment.
Storing and Disposing of Your Medication
To maintain the effectiveness and safety of your medication, store it at room temperature, protected from light, and in a dry place. Avoid storing it in a bathroom, as the moisture and humidity can affect the medication's potency.
Keep all medications in a secure location, out of the reach of children and pets, to prevent accidental ingestion or exposure. When disposing of unused or expired medications, do not flush them down the toilet or pour them down the drain unless specifically instructed to do so by your pharmacist or healthcare provider.
Instead, check with your pharmacist for guidance on the best way to dispose of your medication. You may also want to inquire about drug take-back programs in your area, which can provide a safe and environmentally responsible way to dispose of unwanted medications.
What to Do If You Miss a Dose
If you miss a dose, take it as soon as you remember. However, if it's close to the time for your next scheduled dose, skip the missed dose and resume your regular dosing schedule. Do not take two doses at the same time or take extra doses, as this can increase the risk of side effects or other complications.
Lifestyle & Tips
- Take mexiletine exactly as prescribed by your doctor. Do not stop taking it without consulting your doctor.
- Take with food or a snack to reduce stomach upset.
- Avoid antacids containing aluminum or magnesium within 2 hours of taking mexiletine, as they can reduce its absorption.
- Report any new or worsening symptoms to your doctor immediately.
- Avoid sudden changes in body position to prevent dizziness.
- Limit or avoid alcohol, as it can worsen side effects.
Available Forms & Alternatives
Available Strengths:
Dosing & Administration
Adult Dosing
Standard Dose:
Initial: 200 mg every 8 hours. May be increased or decreased by 50-100 mg increments every 2-3 days. Maintenance: 150-300 mg every 8 hours.
Dose Range:
450 - 1200 mg
Condition-Specific Dosing:
loadingDose:
400 mg once, then 200 mg 8 hours later, then 200 mg 8 hours later, then begin maintenance.
Pediatric Dosing
Neonatal:
Not established
Infant:
Not established
Child:
Not established
Adolescent:
Not established
Dose Adjustments
Renal Impairment:
Mild:
No specific adjustment recommended.
Moderate:
No specific adjustment recommended.
Severe:
Consider lower doses and careful monitoring due to potential accumulation of active metabolites. Monitor for adverse effects.
Dialysis:
Mexiletine is not significantly removed by hemodialysis. No specific supplemental dose needed, but monitor for adverse effects.
Hepatic Impairment:
Mild:
Consider lower doses and careful monitoring.
Moderate:
Reduce dose by 25-50% and monitor closely. Consider therapeutic drug monitoring if available.
Severe:
Reduce dose by 50% or more and monitor closely. Avoid if possible. Consider therapeutic drug monitoring if available.
Pharmacology
Mechanism of Action
Mexiletine is a Class IB antiarrhythmic agent that exerts its electrophysiologic effect by blocking the fast inward sodium current in myocardial cells. This action results in a reduction of the maximum rate of depolarization (Vmax) of the cardiac action potential, particularly in diseased or ischemic tissue. It shortens the action potential duration and effective refractory period, especially in Purkinje fibers and ventricular muscle. It has little or no effect on atrial tissue or AV nodal conduction.
Pharmacokinetics
Absorption:
Bioavailability:
90-95%
Tmax:
2-3 hours
FoodEffect:
Food may delay the rate but not the extent of absorption. Antacids may decrease absorption.
Distribution:
Vd:
5.5-7.0 L/kg
ProteinBinding:
50-60%
CnssPenetration:
Yes
Elimination:
HalfLife:
10-12 hours (range 6-17 hours)
Clearance:
Not available
ExcretionRoute:
Renal (primarily metabolites), Fecal (minor)
Unchanged:
Approximately 10% (increased to 30-40% with acidic urine)
Pharmacodynamics
OnsetOfAction:
30-120 minutes (oral)
PeakEffect:
2-3 hours
DurationOfAction:
8-12 hours
Safety & Warnings
BLACK BOX WARNING
In the National Heart, Lung, and Blood Institute's Cardiac Arrhythmia Suppression Trial (CAST), a long-term, multicenter, randomized, double-blind study in patients with asymptomatic non-life-threatening ventricular arrhythmias who had a myocardial infarction more than 6 days but less than 2 years previously, an excess mortality or nonfatal cardiac arrest rate was seen in patients treated with encainide or flecainide (Class IC antiarrhythmics) compared with that seen in patients assigned to placebo. The findings of the CAST study are applicable to Class I antiarrhythmic drugs. At present, it is prudent to consider that the risks of Class I antiarrhythmics may apply to mexiletine.
Side Effects
Serious Side Effects: Seek Medical Attention Immediately
Although rare, this medication can cause severe and potentially life-threatening side effects. If you experience any of the following symptoms, contact your doctor or seek medical help right away:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Signs of liver problems, including:
+ Dark urine
+ Tiredness
+ Decreased appetite
+ Upset stomach or stomach pain
+ Light-colored stools
+ Vomiting
+ Yellow skin or eyes
Shakiness
Changes in eyesight
Chest pain
Severe dizziness or fainting
Abnormal heartbeat (new or worsening)
Seizures
Changes in balance
Swollen glands
Urination problems (inability to pass urine or changes in urine output)
Muscle pain or weakness
Unexplained bruising or bleeding
Signs of infection, such as fever, chills, or sore throat
Feeling extremely tired or weak
Rarely, this medication can cause low blood cell counts. If you experience any of the above symptoms, contact your doctor immediately.
If you have heart failure, be aware that this medication can worsen your condition. Contact your doctor if you experience:
Shortness of breath
Sudden weight gain
Swelling in the arms or legs
Other Side Effects
Most people taking this medication do not experience serious side effects, and some may not have any side effects at all. However, if you experience any of the following side effects, contact your doctor or seek medical help if they bother you or do not go away:
Feeling nervous or excitable
Dizziness, tiredness, or weakness
Heartburn
Upset stomach or vomiting
Headache
Trouble sleeping
This is not a comprehensive list of all possible side effects. If you have questions or concerns about side effects, contact your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Although rare, this medication can cause severe and potentially life-threatening side effects. If you experience any of the following symptoms, contact your doctor or seek medical help right away:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Signs of liver problems, including:
+ Dark urine
+ Tiredness
+ Decreased appetite
+ Upset stomach or stomach pain
+ Light-colored stools
+ Vomiting
+ Yellow skin or eyes
Shakiness
Changes in eyesight
Chest pain
Severe dizziness or fainting
Abnormal heartbeat (new or worsening)
Seizures
Changes in balance
Swollen glands
Urination problems (inability to pass urine or changes in urine output)
Muscle pain or weakness
Unexplained bruising or bleeding
Signs of infection, such as fever, chills, or sore throat
Feeling extremely tired or weak
Rarely, this medication can cause low blood cell counts. If you experience any of the above symptoms, contact your doctor immediately.
If you have heart failure, be aware that this medication can worsen your condition. Contact your doctor if you experience:
Shortness of breath
Sudden weight gain
Swelling in the arms or legs
Other Side Effects
Most people taking this medication do not experience serious side effects, and some may not have any side effects at all. However, if you experience any of the following side effects, contact your doctor or seek medical help if they bother you or do not go away:
Feeling nervous or excitable
Dizziness, tiredness, or weakness
Heartburn
Upset stomach or vomiting
Headache
Trouble sleeping
This is not a comprehensive list of all possible side effects. If you have questions or concerns about side effects, contact your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- New or worsening irregular heartbeats (palpitations)
- Dizziness or lightheadedness
- Fainting spells
- Severe nausea or vomiting
- Tremors or shaking that is new or worse
- Difficulty with coordination or walking (ataxia)
- Blurred vision or other vision changes
- Signs of liver problems (e.g., yellowing of skin/eyes, dark urine, persistent nausea/vomiting, unusual tiredness)
- Signs of allergic reaction (e.g., rash, itching, swelling, severe dizziness, trouble breathing)
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the symptoms you experienced as a result of the allergy.
If you have heart block, a condition where the electrical signals between your heart's chambers are delayed or blocked.
This list is not exhaustive, and it is crucial to discuss all your medications, including prescription and over-the-counter drugs, natural products, and vitamins, with your doctor and pharmacist. They will help you determine if it is safe to take this medication in combination with your other medications and health conditions.
Remember, do not start, stop, or adjust the dosage of any medication without first consulting your doctor to ensure your safety.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the symptoms you experienced as a result of the allergy.
If you have heart block, a condition where the electrical signals between your heart's chambers are delayed or blocked.
This list is not exhaustive, and it is crucial to discuss all your medications, including prescription and over-the-counter drugs, natural products, and vitamins, with your doctor and pharmacist. They will help you determine if it is safe to take this medication in combination with your other medications and health conditions.
Remember, do not start, stop, or adjust the dosage of any medication without first consulting your doctor to ensure your safety.
Precautions & Cautions
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication. Regular blood work and laboratory tests should be conducted as directed by your doctor to monitor your condition.
A severe and potentially life-threatening reaction can occur, often characterized by symptoms such as fever, rash, or swollen glands, accompanied by problems in various organs, including the liver, kidney, blood, heart, muscles and joints, or lungs. If you have any questions or concerns, consult your doctor for guidance.
If you are pregnant, planning to become pregnant, or are breastfeeding, notify your doctor. You and your doctor will need to discuss the potential benefits and risks of this medication to both you and your baby to make an informed decision.
A severe and potentially life-threatening reaction can occur, often characterized by symptoms such as fever, rash, or swollen glands, accompanied by problems in various organs, including the liver, kidney, blood, heart, muscles and joints, or lungs. If you have any questions or concerns, consult your doctor for guidance.
If you are pregnant, planning to become pregnant, or are breastfeeding, notify your doctor. You and your doctor will need to discuss the potential benefits and risks of this medication to both you and your baby to make an informed decision.
Overdose Information
Overdose Symptoms:
- Severe dizziness or lightheadedness
- Seizures
- Nausea and vomiting
- Slow or irregular heartbeat
- Low blood pressure
- Coma
- Respiratory depression
What to Do:
Seek immediate medical attention or call 911. For poison control, call 1-800-222-1222. Treatment is supportive and may include gastric lavage, activated charcoal, vasopressors for hypotension, and antiarrhythmics for severe arrhythmias.
Drug Interactions
Major Interactions
- CYP2D6 inhibitors (e.g., quinidine, fluoxetine, paroxetine): May significantly increase mexiletine plasma concentrations, increasing risk of toxicity.
- CYP2D6 inducers (e.g., rifampin, phenytoin): May significantly decrease mexiletine plasma concentrations, reducing efficacy.
- Other antiarrhythmics (e.g., amiodarone, quinidine, procainamide): Increased risk of proarrhythmia or additive cardiac effects.
- Drugs that prolong QT interval: Increased risk of Torsades de Pointes (though mexiletine itself has minimal QT effect, caution with other QT prolonging drugs).
Moderate Interactions
- Cimetidine: May increase mexiletine levels.
- Phenobarbital: May decrease mexiletine levels.
- Theophylline: Mexiletine may increase theophylline levels.
- Caffeine: Mexiletine may increase caffeine levels.
- Urinary acidifiers (e.g., ammonium chloride, ascorbic acid): May increase renal excretion of mexiletine, decreasing levels.
- Urinary alkalinizers (e.g., sodium bicarbonate, acetazolamide): May decrease renal excretion of mexiletine, increasing levels.
Minor Interactions
- Antacids (containing aluminum or magnesium): May decrease mexiletine absorption.
Monitoring
Baseline Monitoring
Electrocardiogram (ECG)
Rationale: To assess baseline cardiac rhythm, PR, QRS, and QT intervals, and identify pre-existing conduction abnormalities.
Timing: Prior to initiation of therapy.
Liver Function Tests (LFTs)
Rationale: Mexiletine is extensively metabolized by the liver; to assess baseline hepatic function.
Timing: Prior to initiation of therapy.
Renal Function Tests (BUN, Creatinine)
Rationale: To assess baseline renal function, as a small portion is renally excreted and metabolites may accumulate in severe impairment.
Timing: Prior to initiation of therapy.
Electrolytes (Potassium, Magnesium)
Rationale: Electrolyte imbalances (especially hypokalemia/hypomagnesemia) can exacerbate arrhythmias and reduce antiarrhythmic efficacy.
Timing: Prior to initiation of therapy and correction if abnormal.
Routine Monitoring
Electrocardiogram (ECG)
Frequency: Periodically, or with dose changes/symptom changes.
Target: Stable rhythm, no significant QRS widening (>25% of baseline) or new conduction abnormalities.
Action Threshold: New or worsening arrhythmias, significant QRS widening, new conduction blocks. Consider dose adjustment or discontinuation.
Liver Function Tests (LFTs)
Frequency: Periodically (e.g., every 6-12 months or as clinically indicated).
Target: Within normal limits.
Action Threshold: Significant elevation (e.g., >3x ULN). Consider dose reduction or discontinuation.
Renal Function Tests
Frequency: Periodically (e.g., every 6-12 months or as clinically indicated).
Target: Stable, within normal limits.
Action Threshold: Significant decline in renal function. Consider dose adjustment.
Electrolytes (Potassium, Magnesium)
Frequency: Periodically, especially if on diuretics or with GI upset.
Target: Potassium 4.0-5.0 mEq/L, Magnesium 1.8-2.5 mg/dL.
Action Threshold: Hypokalemia or hypomagnesemia. Correct imbalances promptly.
Mexiletine Plasma Concentrations (Therapeutic Drug Monitoring)
Frequency: Consider for patients with renal/hepatic impairment, suspected toxicity, or lack of efficacy. Not routinely recommended for all patients.
Target: 0.5-2.0 mcg/mL (some sources suggest 0.7-2.0 mcg/mL).
Action Threshold: Levels >2.0 mcg/mL (increased risk of CNS and GI side effects, proarrhythmia). Levels <0.5 mcg/mL (potential for subtherapeutic effect).
Symptom Monitoring
- Dizziness
- Tremor
- Ataxia
- Nausea
- Vomiting
- Heart palpitations
- Chest pain
- Shortness of breath
- Lightheadedness
- Syncope
- Blurred vision
- Numbness or tingling
Special Patient Groups
Pregnancy
Category C. Animal studies have shown adverse effects on the fetus. There are no adequate and well-controlled studies in pregnant women. Mexiletine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Trimester-Specific Risks:
First Trimester:
Potential for teratogenicity based on animal data. Use only if clearly needed.
Second Trimester:
Potential for fetal adverse effects. Monitor fetal heart rate and growth.
Third Trimester:
Potential for fetal adverse effects. Monitor fetal heart rate and growth.
Lactation
L3 (Moderately Safe). Mexiletine is excreted into breast milk. The amount ingested by the infant is generally low, but potential for adverse effects (e.g., bradycardia, CNS depression) exists. Monitor breastfed infant for signs of adverse effects.
Infant Risk:
Low to moderate risk. Monitor for bradycardia, lethargy, feeding difficulties.
Pediatric Use
Safety and efficacy in pediatric patients have not been established. Use is generally not recommended.
Geriatric Use
Use with caution in elderly patients, as they may be more susceptible to adverse effects due to age-related decreases in hepatic and renal function. Start with lower doses and titrate slowly. Monitor closely for CNS and cardiac adverse effects.
Clinical Information
Clinical Pearls
- Mexiletine is primarily used for ventricular arrhythmias, especially in patients with structural heart disease, where other antiarrhythmics might be contraindicated or less effective.
- It is often used off-label for neuropathic pain, particularly painful diabetic neuropathy, but this information is not for the 150mg capsule formulation which is indicated for arrhythmias.
- The black box warning regarding increased mortality in post-MI patients with asymptomatic arrhythmias is a critical consideration, similar to other Class I antiarrhythmics.
- GI side effects (nausea, vomiting, heartburn) are common and can be minimized by taking the medication with food or antacids (non-aluminum/magnesium containing).
- CNS side effects (tremor, dizziness, ataxia) are dose-related and often indicate toxicity; therapeutic drug monitoring can be helpful in these cases.
- Mexiletine's metabolism is highly dependent on CYP2D6, making drug interactions with CYP2D6 inhibitors or inducers clinically significant.
Alternative Therapies
- Other Class I antiarrhythmics (e.g., lidocaine IV, procainamide, quinidine, flecainide, propafenone)
- Class II antiarrhythmics (beta-blockers)
- Class III antiarrhythmics (e.g., amiodarone, sotalol, dofetilide)
- Class IV antiarrhythmics (calcium channel blockers, e.g., verapamil, diltiazem)
- Catheter ablation for ventricular arrhythmias
- Implantable Cardioverter-Defibrillator (ICD)
Cost & Coverage
Average Cost:
$50 - $200+ per 30 capsules (150mg)
Generic Available:
Yes
Insurance Coverage:
Tier 1 or Tier 2 (Generic)
General Drug Facts
If your symptoms or health issues persist or worsen, it is essential to contact your doctor promptly. To ensure your safety, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so it's a good idea to check with your pharmacist. If you have any questions or concerns about this medication, don't hesitate to discuss them with your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek emergency medical attention. When seeking help, be prepared to provide detailed information about the overdose, including the medication taken, the amount, and the time it occurred.