Mexiletine is an antiarrhythmic agent. It is used to treat ventricular arrhythmias (irregular heart beats associated with the ventricles of the heart). It is often used in conjunction with other heart medications.
- The most common side effects are related to the GI tract including nausea and vomiting. Giving food with mexiletine has been shown to decrease the incidence of GI side effects.
- Other possible side effects include central nervous system signs such as dizziness, loss of balance and trembling, shortness of breath, and cardiac signs including PVCs or chest pain.
- Rare side effects reported in humans include seizures, and bone marrow suppression.
- Mexiletine should be used with extreme caution in animals with the following conditions: 2nd or 3rd degree AV heart block, intraventricular conduction abnormality, sinus node function abnormality, cardiogenic shock, congestive heart failure, myocardial infarction, liver dysfunction, hypotension, or seizure disorders.
- Concurrent use with lidocaine increases the likelihood of adverse effects.
- There are a number of drugs that may cause drug interactions either through changing the rate of absorption or changing the rate of metabolism of mexiletine. This list includes: antacids, atropine, opiates, cimetidine, griseofulvin, metoclopramide, phenobarbital, phenytoin, primidone, rifampin, theophylline.
- Drugs which change urinary acidity may affect the renal excretion of mexiletine. These drugs include methionine, ammonium chloride, potassium phosphate, sodium phosphate, citrates, sodium bicarbonate, and carbonic anhydrase inhibitors.
Overdose with mexiletine carries a significant risk of toxicity. It is reported in the human literature that central nervous system signs precede cardiovascular signs. In experimental work in dogs, a four fold overdose consistently produced CNS signs within 10 minutes of oral administration. If recognized in time, GI emptying protocol should be attempted in conjunction with urinary acidification and supportive care.