Mexiletine

INTRODUCTION

Indications

Prophylaxis/treatment of serious ventricular arrhythmias, including ventricular tachycardia (VT) and premature ventricular contractions (PVCs). Unlabeled Use: Management of chronic neuropathic pain.

Action

Decreases the duration of the action potential and effective refractory period in cardiac conduction tissue by altering transport of sodium across myocardial cell membranes. Has little or no effect on heart rate. Therapeutic Effects: Control of ventricular arrhythmias.

Adverse Reactions/Side Effects

CNS: dizziness, nervousness, confusion, fatigue, headache, sleep disorder. EENT: blurred vision, tinnitus. Resp: dyspnea. CV: ARRHYTHMIAS, chest pain, edema, palpitations. GI: HEPATIC NECROSIS, heartburn, nausea, vomiting. Derm: rashes. Hemat: blood dyscrasias. Neuro: tremor, coordination difficulties, paresthesia.

PHYSICAL THERAPY IMPLICATIONS

Examination and Evaluation

• Assess heart rate, ECG, and heart sounds, especially during exercise (See Appendices G, H). Although intended to treat certain arrhythmias, this drug can unmask or precipitate new arrhythmias (proarrhythmic effect). Report any rhythm disturbances or symptoms of increased arrhythmias, including palpitations, chest pain, shortness of breath, fainting, and fatigue/weakness.

• Be alert for signs of liver dysfunction and hepatic necrosis, including anorexia, abdominal pain, severe nausea and vomiting, yellow skin or eyes, fever, sore throat, malaise, weakness, facial edema, lethargy, and unusual bleeding or bruising. Report these signs to the physician immediately.

• Monitor signs of blood dyscrasias including agranulocytosis (fever, sore throat, mucosal lesions, other signs of infection), thrombocytopenia (bruising, nose bleeds, bleeding gums), or anemia (unusual fatigue, shortness of breath, dizziness, headache, coldness in your hands and feet, pale skin, chest pain). Report these signs to the physician.

• Assess peripheral edema using girth measurements, volume displacement, and measurement of pitting edema (See Appendix N). Report increased swelling in feet and ankles or a sudden increase in body weight due to fluid retention.

• Assess signs of parasthesia (numbness, tingling) or tremor. Perform objective tests including electroneuromyography and sensory testing to document any drug-related neuropathic changes.

• If treating neuropathic pain, use visual analogue scales and other appropriate pain scales to assess the patient's pain and help document the effects of drug therapy.

• Monitor nervousness, confusion, or other changes in mood and behavior. Notify physician if these changes become problematic.

• Assess dizziness or incoordination that might affect gait, balance, and other functional activities (See Appendix C). Report balance problems and functional limitations to the physician, and caution the patient and family/caregivers to guard against falls and trauma.

Interventions

• Because of the risk of serious cardiac arrhythmias, use extreme caution during aerobic exercise and other forms of therapeutic exercise. Assess exercise tolerance frequently (blood pressure, heart rate, fatigue levels), and terminate exercise immediately if any untoward responses occur (See Appendix L...