mexiletine

• Risk factor: Recent heart attack

According to a clinical trial known as The Cardiac Arrhythmia Suppression Trial (CAST), people who had recent history of heart attack and took antiarrhythmic medications similar to mexiletine were at greater risk of sudden death or sudden heart stop (cardiac arrest). If you've had a heart attack within the last 2 years, this medication might not be safe for you. Talk to your provider about what is the best medication for your heart. Your provider will decide which medication is best for you based on your symptoms and electrocardiogram (EKG) results.

• Risk factors: Heart failure | Heart attack | Receiving blood transfusion | Not enough blood flow to the heart | First few weeks of treatment

Though rare, there have been reports of people who developed serious liver problems while taking mexiletine. Most of the time, it happened within the first few weeks of treatment and to people who also had other heart problems, such as heart failure or blood vessel problems. It's unclear whether the liver problems can be linked to mexiletine. To be safe, your provider might ask you to get blood tests done regularly while you take mexiletine so your provider can check your liver health. If you experience signs and symptoms of liver damage, such as feeling sleepy, upper right stomach pain, yellowing of the skin or eyes, or dark urine, please talk with your provider right away.

In some rare cases, mexiletine can cause severe allergic reactions, such as drug reaction with eosinophilia and systemic symptoms (DRESS). These reactions can happen with or without a rash and can sometimes lead to organ failure or blood problems. Make sure to get medical help right away if you have signs like sudden rash, mouth sores, fever, chills, body aches, or swollen lymph nodes.

Antiarrhythmic medications like mexiletine can sometimes worsen abnormal heart rhythms. This is because the medication slows down the electrical activity in certain parts of the heart, which can lead to life-threatening arrhythmias. As a result, your first dose is often given in the hospital, so that your provider can monitor your heart's electrical activity using an EKG. Make sure to follow up with your provider regularly after starting treatment so they can make sure this medication is safe for you. If you notice an abnormally slow or fast pulse, chest pain or discomfort, weakness, dizziness, or fainting while taking mexiletine, get medical help right away.

• Risk factors: Existing low blood pressure | Severe congestive heart failure

If you already have heart failure or low blood pressure, taking mexiletine might make your condition worse. Make sure your provider knows your medical history so they can make sure it's safe for you to take mexiletine. Let your provider know right away if you have symptoms of low blood pressure (e.g, dizziness, lightheadedness, fainting) or heart failure (e.g., shortness of breath, swelling of feet or ankles). You might need to stop taking mexiletine.

• Risk factors: Serious illness | Taking medications that lower blood cell counts

Though extremely rare, some people developed lower white blood cell (WBC) count and platelet count while taking mexiletine. This can put you at higher risk for infections and bleeds. Your blood cell counts typically return to the normal range within a month of stopping mexiletine. Let your provider know if you've symptoms of infection (e.g., fever, chills, diarrhea, sore throat) or bleeding (e.g., abnormal bruising)

Some medications can interfere with how your body gets rid of mexiletine from your system. This can affect the amount of mexiletine in your body, how well it works, and the risk of side effects.

When taken with mexiletine, certain medications can lower the amount of mexiletine in your body and cause it to not work as well. Because of this effect, your provider might ask you to avoid taking mexiletine with certain medications, such as phenytoin (Dilantin) or rifampin (Rifadin).

Mexiletine can also affect how your body absorbs other medications. For example, mexiletine can cause your body to absorb more theophylline, a medication for certain lung problems (e.g., asthma). This can lead to more theophylline side effects, such as nausea, vomiting, and trouble sleeping. Make sure your provider and pharmacist have a full list of medications and supplements you're taking before starting mexiletine.