Mexiletine

Indications

Mexiletine is used for: Ventricular arrhythmias

Adult Dose

Oral Ventricular Arrhythmias (Life-Threatening) Initial: 200 mg PO q8hr; may load with 400 mg followed by 200 mg PO q8hr if necessary for rapid control of ventricular arrhythmia Dose range: 200-300 mg PO q8hr May increase to 400 mg q8hr; not to exceed 1200 mg/day Take with food or antacid Therapeutic range: 0.5-2 mg/L

Child Dose

Renal Dose

Administration

Should be taken with food.

Contra Indications

Cardiogenic shock, 2nd- or 3rd-degree AV block (unless the patient has a pacemaker).

Precautions

Acute MI, sinus node dysfunction, conduction defects, bradycardia, hypotension, heart failure, hepatic impairment. Monitor ECG and BP. Correct electrolyte imbalance prior to and during therapy. Pregnancy.

Pregnancy-Lactation

Pregnancy Category: C Lactation: enters breast milk at concs comparable to maternal plasma (AAP Committee states compatible w/ nursing)

Interactions

Levels/effects may be reduced with CYP1A2 inducers (e.g. aminoglutethimide, carbamazepine, phenobarbital, rifampicin). Levels/effects may be increased with CYP1A2 inhibitors (e.g. ciprofloxacin, ketoconazole, norfloxacin, ofloxacin, rofecoxib), CYP2D6 inhibitors (e.g. chlorpromazine, delavirdine, fluoxetine, miconazole, paroxetine, pergolide, quinidine, quinine, ritonavir, ropinirole) and urinary alkalinisers (e.g. antacids, sodium bicarbonate, acetazolamide). May increase the levels/effects of CYP1A2 substrates e.g. aminophylline, fluvoxamine, mirtazapine, ropinirole, theophylline, trifluoperazine. Clearance reduced with fluvoxamine. Delayed absorption with opioid analgesics. Potentially Fatal: Increased risk of arrhythmias with other antiarrhythmics or arrhythmogenic drugs. May precipitate lidocaine toxicity.

Adverse Effects

Side effects of Mexiletine : >10% Nausea (40%) Vomiting (40%) Heartburn (40%) Ataxia (20%) Dizziness (20-25%%) Lightheadedness (11-25%) Tremor (13%) 1-10% Coordination difficulties (10%) Palpitation (4-7%) Hypotension (4-8%) Angina (2%) Headache (5-7%) Depression (2%) Xerostomia (3%) Proarrythmia (10-15%) Rash (4%) Insomnia (5-7%) Confusion (5-7%) Chest pain (3-8%) Abdominal pain (1%) Dyspnea (3%) Constipation or diarrhea (4-5%) Premature ventricular contractions (1-2%) Blurred vision (5-7%) Nystagmus (6%) Frequency Not Defined Edema Exacerbation of CHF Puilmonary fibrosis Proarrhythmia Convulsions Mouth sores Tinnitus Systemic lupus erythematosus

Mechanism of Action

Mexiletine is a class Ib antiarrhythmic. It inhibits inward sodium current which decreases the rate of depolarisation of phase 0 of the action potential. It also increases effective refractory period (ERP) relative to the action potential duration (ERP/APD).