Mexiletine Drug Handout

What is Mexiletine?

Mexiletine is an oral medication belonging to a group of medications known as antiarrhythmics. Its job is to slow electrical impulses through the heart and to make the heart cells less sensitive to stimulation. Mexiletine has less effect on overall heart rate and heart muscle strength in comparison to some of the other commonly used antiarrhythmics.


  • Treats ventricular arrhythmias (ventricular premature complexes/VPCs or ventricular tachycardia) most commonly associated with Dilated Cardiomyopathy or Arrhythmogenic Right Ventricular Cardiomyopathy
  • Less commonly used in the control of rapid heart rates caused by a congenital accessory pathway

Adverse Effects

Please contact CVCA should any of these symptoms be noted

  • Decreased appetite, vomiting and diarrhea are the most commonly associated side effect
  • Trembling, shivering, dizziness or depression occur much less frequently

Client Information

  • Best given with food to avoid stomach upset
  • Most commonly given three times a day (every 8 hours), however dosing 1-2 hours early/late should be fine to fit into your schedule
  • Please do not abruptly stop the medication, skip or lower the dose without veterinary approval
  • Most commonly given in capsule Can be reformulated into appropriately sized capsules or liquid for small dogs
  • Not a medication normally used in cats due to their increased sensitivity and risk for seizures
  • Monitoring by auscultation, ECG and Holter monitor will help to determine if the medication is controlling the abnormal heart rhythm
  • Potassium levels may need to be monitored, as Mexiletine is more effective in the face of normal blood potassium levels
  • Often used in combination with other antiarrhythmic drugs in cases of difficult to control arrhythmias (Sotalol, Atenolol)
  • Certain breeds may be more sensitive to the drugs effects (herding type breeds/ MDR1 defect)

Interaction with Other Drugs

Standard Dosage Forms

Synonyms: (Mexiletine, Mexitil)