Mexiletine

Indications
 Oral
Ventricular arrhythmias
Adult: As hydrochloride: 400 mg as loading dose followed after 2 hr by 200-250 mg 3-4 times daily. Maintenance: 600-900 mg daily in divided doses. Max dose: 1200 mg daily. Patient with MI: Higher loading dose e.g. 600 mg may be needed, especially if opioid analgesics were also given.
Renal impairment: Dose reduction may be needed.
Hepatic impairment: Dose reduction may be needed.
Intravenous
Ventricular arrhythmias
Adult: As hydrochloride: 100-250 mg slow inj at 25 mg/min followed by 250 mg infusion over 1 hr, 250 mg for the next 2 hr and then 0.5 mg/min for maintenance, according to response. Transfer to oral dose of 200-250 mg 3-4 times daily when possible. Alternatively, 200 mg at 25 mg/min followed by 400 mg orally upon completion of inj, with subsequent oral dose of 200-250 mg 3-4 times daily.
Renal impairment: Dose reduction may be needed.
Hepatic impairment: Dose reduction may be needed.
Contraindications
 Cardiogenic shock, 2nd- or 3rd-degree AV block (unless the patient has a pacemaker).
Warnings / 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.
Adverse Reactions
 Nausea, vomiting, diarrhoea, constipation, oesophageal ulceration, confusion, lightheadedness, blurred vision, sleep disturbances, speech difficulties, exacerbated arrhythmias, hepatotoxicity, dizziness, tremor, nervousness, ataxia, sinus bradycardia, AV dissociation and atrial fibrillation.
Potentially Fatal: Cardiogenic shock, hepatic necrosis, Stevens-Johnson syndrome, heart block, sinus arrest.
Overdose Reactions
 With narrow therapeutic index; acute ingestion of twice the daily therapeutic dose may be life-threatening. Symptoms: Sedation, confusion, coma, seizures, respiratory arrest, sinus arrest, AV block, asystole, hypotension, dizziness, paraesthesia, tremor, ataxia, GI disturbance. Prolonged QRS and QT intervals (massive overdose). Management: Symptomatic and supportive.
Drug 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.
See Below for More mexiletine Drug Interactions
Food Interactions
 Food may reduce rate but not the extent of oral absorption. Avoid dietary changes that alter urine pH since these may increase or decrease excretion of mexiletine.
Mechanism of Actions
 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).
Absorption: Readily and almost completely absorbed from the GI tract (oral); may be delayed after MI.
Distribution: Distributed widely; crosses the placenta and enters breast milk. Protein-binding: 50-70%.
Metabolism: Hepatic via cytochrome P450 isoenzymes CYP1A2, CYP2D6, CYP3A4.
Excretion: Via urine (mainly as metabolites and 10% unchanged drug). Clearance increased in acid urine. Elimination half-life: 10 hr; may be prolonged in heart disease, hepatic impairment and severe renal impairment.
Administration
 Should be taken with food.
ATC Classification
 C01BB02 - mexiletine ; Belongs to class Ib antiarrhythmics.
Available As
  • Mexiletine 150 mg
  • Mexiletine 250 mg
  • Mexiletine 50 mg

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