Mexiletine 250mg 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
Oct 1985
DEA Schedule
Not Controlled
Overview
What is this medicine?
Mexiletine is a medication used to treat certain types of irregular heartbeats (ventricular arrhythmias). It works by affecting the electrical signals in your heart to help it beat more regularly. It can also be used off-label for certain muscle conditions like myotonia.
How to Use This Medicine
Taking Your Medication
To use this medication correctly, follow your doctor's instructions and read all the information provided. Take this medication with food or an antacid to help your body absorb it properly. Continue taking the medication as directed by your doctor or healthcare provider, even if you start to feel better.
Storing and Disposing of Your Medication
Store this medication at room temperature, away from light and moisture. Keep it in a dry place, such as a closet or cupboard, and avoid storing it in the bathroom. Keep all medications out of the reach of children and pets to ensure their safety. When you no longer need this medication or it has expired, dispose of it properly. Do not flush it down the toilet or pour it down the drain unless instructed to do so by your pharmacist. If you have questions about disposing of your medication, ask your pharmacist for guidance. You may also want to check if there are any drug take-back programs in your area.
Missing 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 continue with your regular dosing schedule. Do not take two doses at the same time or take extra doses to make up for a missed one.
To use this medication correctly, follow your doctor's instructions and read all the information provided. Take this medication with food or an antacid to help your body absorb it properly. Continue taking the medication as directed by your doctor or healthcare provider, even if you start to feel better.
Storing and Disposing of Your Medication
Store this medication at room temperature, away from light and moisture. Keep it in a dry place, such as a closet or cupboard, and avoid storing it in the bathroom. Keep all medications out of the reach of children and pets to ensure their safety. When you no longer need this medication or it has expired, dispose of it properly. Do not flush it down the toilet or pour it down the drain unless instructed to do so by your pharmacist. If you have questions about disposing of your medication, ask your pharmacist for guidance. You may also want to check if there are any drug take-back programs in your area.
Missing 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 continue with your regular dosing schedule. Do not take two doses at the same time or take extra doses to make up for a missed one.
Lifestyle & Tips
- Take mexiletine exactly as prescribed, usually with food or antacids to reduce stomach upset.
- Do not stop taking this medication suddenly without consulting your doctor, as it can worsen your heart condition.
- Avoid grapefruit juice as it may affect how your body processes the medication.
- Limit or avoid alcohol consumption, as it can worsen side effects.
- Report any new or worsening symptoms to your doctor immediately.
Available Forms & Alternatives
Available Strengths:
Dosing & Administration
Adult Dosing
Standard Dose:
Initial: 200 mg every 8 hours. May be initiated with a 400 mg loading dose, followed by 200 mg 8 hours later, then 200 mg 8 hours later. Maintenance: 200-300 mg every 8 hours.
Dose Range:
600 - 1200 mg
Condition-Specific Dosing:
ventricularArrhythmias:
Initial: 200 mg every 8 hours. May be initiated with a 400 mg loading dose, followed by 200 mg 8 hours later, then 200 mg 8 hours later. Maintenance: 200-300 mg every 8 hours. Max 1200 mg/day.
myotoniaCongenita (off-label):
150-200 mg three times daily, titrated to effect. Max 600 mg/day.
Pediatric Dosing
Neonatal:
Not established for arrhythmias. Used off-label for myotonia: 1-2 mg/kg/dose every 8 hours, titrate to effect (max 10 mg/kg/day or 400 mg/day).
Infant:
Not established for arrhythmias. Used off-label for myotonia: 1-2 mg/kg/dose every 8 hours, titrate to effect (max 10 mg/kg/day or 400 mg/day).
Child:
Not established for arrhythmias. Used off-label for myotonia: 1-2 mg/kg/dose every 8 hours, titrate to effect (max 10 mg/kg/day or 400 mg/day).
Adolescent:
Not established for arrhythmias. Used off-label for myotonia: 1-2 mg/kg/dose every 8 hours, titrate to effect (max 10 mg/kg/day or 400 mg/day).
Dose Adjustments
Renal Impairment:
Mild:
No specific adjustment, monitor closely.
Moderate:
No specific adjustment, monitor closely.
Severe:
Consider reducing dose by 30-50% or extending dosing interval. Monitor serum levels.
Dialysis:
Not significantly dialyzable. No supplemental dose needed post-dialysis. Monitor closely.
Hepatic Impairment:
Mild:
Consider reducing dose by 25%.
Moderate:
Reduce dose by 30-50%. Monitor serum levels closely.
Severe:
Reduce dose by 50% or more. Monitor serum levels closely. Avoid if possible.
Confidence:
Medium
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 reduces the maximum rate of depolarization (Vmax) of the cardiac action potential, particularly in ischemic or damaged tissue, without significantly affecting repolarization. It shortens the effective refractory period and action potential duration in Purkinje fibers and ventricular muscle. It has little or no effect on atrial tissue or AV nodal conduction.
Pharmacokinetics
Absorption:
Bioavailability:
90%
Tmax:
2-3 hours
FoodEffect:
Food may delay the rate of absorption but does not significantly affect the extent of absorption. Administration with food or antacids may reduce gastrointestinal upset.
Distribution:
Vd:
5-7 L/kg
ProteinBinding:
50-60%
CnssPenetration:
Yes
Elimination:
HalfLife:
10-12 hours (can range from 6-17 hours; prolonged in hepatic impairment)
Clearance:
Not available (primarily hepatic metabolism)
ExcretionRoute:
Primarily hepatic metabolism with subsequent renal excretion of metabolites. Less than 10% excreted unchanged in urine.
Unchanged:
<10%
Pharmacodynamics
OnsetOfAction:
30 minutes to 2 hours (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 myocardial infarction more than 6 days previously, an excess mortality and nonfatal cardiac arrest rate was seen in patients treated with encainide or flecainide (Class IC antiarrhythmics) compared with that seen in patients in the placebo group. The findings of the CAST study are applicable to mexiletine, a Class IB antiarrhythmic, due to similar electrophysiologic effects. The risk of proarrhythmia with mexiletine should be weighed against the potential benefits.
Side Effects
Urgent Side Effects: Seek Medical Help Right Away
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor or seek immediate medical attention:
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 (difficulty starting or stopping urination, 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. Discuss this with your doctor and seek medical help right away if you experience:
Shortness of breath
Sudden weight gain
Swelling in the arms or legs
Other Possible Side Effects
Most people taking this medication do not experience severe side effects, and some may not have any side effects at all. However, if you notice any of the following symptoms, 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 an exhaustive list of 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, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor or seek immediate medical attention:
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 (difficulty starting or stopping urination, 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. Discuss this with your doctor and seek medical help right away if you experience:
Shortness of breath
Sudden weight gain
Swelling in the arms or legs
Other Possible Side Effects
Most people taking this medication do not experience severe side effects, and some may not have any side effects at all. However, if you notice any of the following symptoms, 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 an exhaustive list of 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, fainting)
- Severe dizziness, lightheadedness, or fainting
- Tremor, unsteadiness, or difficulty with coordination (ataxia)
- Blurred vision or double vision
- Numbness or tingling in hands or feet (paresthesias)
- Seizures
- Severe nausea, vomiting, or stomach pain
- Yellowing of skin or eyes (jaundice), dark urine, unusual tiredness (signs of liver problems)
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 allergic reaction you experienced, including any symptoms that occurred.
If you have heart block, a condition where the electrical signals between the chambers of your heart are partially or completely 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 change the dose 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 allergic reaction you experienced, including any symptoms that occurred.
If you have heart block, a condition where the electrical signals between the chambers of your heart are partially or completely 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 change the dose 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 may occur, 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.
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.
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 may occur, 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.
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.
Overdose Information
Overdose Symptoms:
- Severe nausea and vomiting
- Drowsiness, confusion, disorientation
- Seizures
- Hypotension (low blood pressure)
- Bradycardia (slow heart rate)
- Asystole (cardiac arrest)
- Coma
What to Do:
Seek immediate medical attention. Call 911 or your local emergency number. For poison control, call 1-800-222-1222. Management may include gastric lavage, activated charcoal, supportive care, and treatment of seizures (e.g., IV diazepam or phenytoin), hypotension (e.g., IV fluids, vasopressors), and arrhythmias (e.g., atropine for bradycardia, pacing).
Drug Interactions
Major Interactions
- CYP2D6 inhibitors (e.g., quinidine, fluoxetine, paroxetine): May significantly increase mexiletine plasma concentrations, increasing risk of toxicity. Dose reduction of mexiletine may be required.
- CYP2D6 inducers (e.g., rifampin, phenytoin, phenobarbital): May significantly decrease mexiletine plasma concentrations, reducing efficacy. Dose increase of mexiletine may be required.
- Theophylline: Mexiletine inhibits the metabolism of theophylline, leading to increased theophylline levels and potential toxicity. Monitor theophylline levels closely.
- Caffeine: Mexiletine inhibits caffeine metabolism, leading to increased caffeine levels and potential toxicity.
Moderate Interactions
- Drugs that prolong QT interval (e.g., amiodarone, sotalol, tricyclic antidepressants, some antipsychotics): Although mexiletine itself has minimal effect on QT, caution is advised with other QT-prolonging drugs due to potential additive effects in susceptible individuals.
- Antacids (e.g., aluminum hydroxide, magnesium hydroxide): May decrease the rate and extent of mexiletine absorption. Separate administration times.
- Opioids (e.g., morphine): May delay gastric emptying, potentially delaying mexiletine absorption.
- Metoclopramide: May increase the rate of mexiletine absorption.
- Cimetidine: May increase mexiletine levels due to inhibition of hepatic metabolism (less significant than CYP2D6 inhibitors).
Minor Interactions
- Urinary acidifiers (e.g., ammonium chloride): May increase renal excretion of mexiletine.
- Urinary alkalinizers (e.g., sodium bicarbonate): May decrease renal excretion of mexiletine.
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.
Serum Electrolytes (Potassium, Magnesium)
Rationale: Electrolyte imbalances (especially hypokalemia, hypomagnesemia) can exacerbate arrhythmias and reduce antiarrhythmic efficacy. Correct imbalances before starting therapy.
Timing: Prior to initiation of therapy.
Liver Function Tests (LFTs)
Rationale: Mexiletine is extensively metabolized by the liver; baseline assessment is crucial, especially in patients with suspected hepatic impairment.
Timing: Prior to initiation of therapy.
Renal Function Tests (Creatinine, BUN)
Rationale: Although primarily hepatically metabolized, a small percentage is renally excreted unchanged. Renal impairment can affect metabolite excretion.
Timing: Prior to initiation of therapy.
Routine Monitoring
Electrocardiogram (ECG)
Frequency: Periodically, or with dose adjustments, or if new arrhythmias/symptoms develop.
Target: Stable PR, QRS, and QT intervals; absence of proarrhythmia.
Action Threshold: Significant widening of QRS (>25% of baseline), new conduction blocks, or proarrhythmia warrants dose reduction or discontinuation.
Serum Mexiletine Levels
Frequency: Initially after reaching steady state (3-5 half-lives), then periodically or with dose changes/suspected toxicity/lack of efficacy.
Target: 0.5-2.0 mcg/mL (therapeutic range)
Action Threshold: Levels >2.0 mcg/mL increase risk of CNS and GI side effects; levels <0.5 mcg/mL may indicate subtherapeutic dosing. Adjust dose accordingly.
Serum Electrolytes (Potassium, Magnesium)
Frequency: Periodically, especially if on diuretics or with GI disturbances.
Target: Within normal limits (K: 3.5-5.0 mEq/L, Mg: 1.7-2.2 mg/dL)
Action Threshold: Correct hypokalemia or hypomagnesemia promptly.
Liver Function Tests (LFTs)
Frequency: Periodically, especially in patients with pre-existing hepatic impairment or if symptoms of liver dysfunction develop.
Target: Within normal limits.
Action Threshold: Significant elevation of liver enzymes warrants investigation and potential dose adjustment or discontinuation.
Symptom Monitoring
- Worsening of arrhythmias (e.g., increased palpitations, dizziness, syncope)
- Central nervous system effects (e.g., dizziness, tremor, ataxia, confusion, nystagmus, blurred vision, paresthesias, seizures)
- Gastrointestinal effects (e.g., nausea, vomiting, heartburn, dyspepsia, abdominal pain)
- Cardiovascular effects (e.g., bradycardia, hypotension, chest pain)
- Signs of liver dysfunction (e.g., jaundice, dark urine, persistent nausea/vomiting)
Special Patient Groups
Pregnancy
Mexiletine is classified as Pregnancy Category C. Animal studies have shown adverse effects on the fetus, but 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; human data limited.
Second Trimester:
Potential for fetal exposure and effects on cardiac development; human data limited.
Third Trimester:
Potential for fetal exposure and effects on cardiac function; human data limited.
Lactation
Mexiletine is excreted into breast milk. The amount of mexiletine excreted is relatively low, but potential for adverse effects in the infant exists (e.g., bradycardia, CNS depression). The American Academy of Pediatrics considers mexiletine to be a drug for which the effect on the nursing infant is unknown but may be of concern. Use with caution; monitor infant for adverse effects.
Infant Risk:
L3 (Moderately Safe) - Monitor infant for bradycardia, CNS depression, feeding difficulties.
Pediatric Use
Safety and efficacy for the treatment of ventricular arrhythmias in pediatric patients have not been established. Mexiletine is used off-label for the treatment of myotonia in pediatric patients, with dosing based on weight and titrated to effect. Close monitoring for adverse effects is crucial.
Geriatric Use
Elderly patients may have reduced hepatic and/or renal function, leading to decreased clearance and increased plasma concentrations of mexiletine. Start with lower doses and titrate slowly, monitoring for adverse effects and serum levels. Increased sensitivity to CNS and GI side effects may occur.
Clinical Information
Clinical Pearls
- Mexiletine is a Class IB antiarrhythmic, similar to lidocaine, but orally active.
- It is primarily used for ventricular arrhythmias, especially those associated with myocardial infarction or digitalis toxicity.
- Always administer with food or antacids to minimize GI side effects (nausea, vomiting, heartburn), which are common.
- Therapeutic drug monitoring (TDM) is recommended due to narrow therapeutic index and significant inter-patient variability in metabolism.
- Be aware of the black box warning regarding increased mortality in post-MI patients with non-life-threatening arrhythmias.
- Significant drug interactions exist, particularly with CYP2D6 inhibitors/inducers and theophylline. Review patient's medication list carefully.
- While primarily used for arrhythmias, its off-label use for myotonia is well-established and often effective.
Alternative Therapies
- Other Class I antiarrhythmics (e.g., flecainide, propafenone, quinidine, procainamide, disopyramide - note different subclasses and side effect profiles)
- Class II antiarrhythmics (beta-blockers, e.g., metoprolol, carvedilol)
- Class III antiarrhythmics (e.g., amiodarone, sotalol, dofetilide)
- Class IV antiarrhythmics (calcium channel blockers, e.g., verapamil, diltiazem - for supraventricular arrhythmias, less for ventricular)
- Catheter ablation (for refractory arrhythmias)
- Implantable cardioverter-defibrillator (ICD) (for high-risk patients with life-threatening arrhythmias)
Cost & Coverage
Average Cost:
Varies widely, typically $50-$300+ per 30 capsules
Generic Available:
Yes
Insurance Coverage:
Tier 2 or Tier 3 (generic)
General Drug Facts
If your symptoms or health issues persist or worsen, it is essential to contact your doctor promptly. To ensure safe and effective treatment, 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 reporting the incident, be prepared to provide details about the medication taken, the amount, and the time it occurred.