Adult: In patients with non-dystrophic myotonic disorders: Initially, 167 mg once daily. Doses may be increased based on the clinical response to 333 mg daily after at least 1 week, then may further increase to 500 mg daily after at least 1 further week of treatment. Maintenance: 167-500 mg daily. Max: 500 mg daily.
Oral Ventricular arrhythmias
Adult: For rapid control of life-threatening cases: 400 mg loading dose, followed by 200 mg 8 hourly. When rapid control of life-threatening cases is not essential: Initially, 200 mg 8 hourly. Doses may be adjusted in increments or decrements of 50 or 100 mg at intervals of at least 2-3 days. Usual dose: 200-300 mg 8 hourly. Max: 400 mg 8 hourly. Treatment-responsive patients may be transferred to 12 hourly dosage schedule; if necessary, doses may be adjusted up to Max 450 mg 12 hourly.
Dosage adjustment may be needed. Myotonia:
Mild to moderate: Dose may be increased only after at least 2 weeks of treatment.
Should be taken with food.
Cardiogenic shock, 2nd- or 3rd-degree atrioventricular (AV) block (without the presence of pacemaker).
Patient with 1st-degree AV block, sinus node dysfunction, intraventricular conduction disturbances, CHF, hypotension, seizure disorders, and electrolyte imbalance (e.g. hypo- or hyperkalaemia, hypomagnesaemia); MI, abnormal Q-waves, symptomatic coronary artery disease, ventricular or atrial tachyarrhythmia, atrial flutter or fibrillation (for use in myotonia). Concomitant use with agents known to induce torsades de pointes. Treatment guidelines may vary among individual products (refer to product-specific recommendations). Hepatic impairment. Pregnancy and lactation.
Significant: Proarrhythmic effects (e.g. proarrhythmia, aggravation of arrhythmia), blood dyscrasias (e.g. leucopenia, agranulocytosis, thrombocytopenia), abnormal LFTs (e.g. markedly raised AST), drug reactions with eosinophilia and systemic symptoms (DRESS), seizures. Rarely, severe liver injury, hepatic necrosis. Cardiac disorders: Tachycardia, palpitations, chest pain. Ear and labyrinth disorders: Vertigo, tinnitus. Eye disorders: Blurred vision, nystagmus. Gastrointestinal disorders: Abdominal pain, nausea, vomiting, diarrhoea, constipation, heartburn. General disorders and administration site conditions: Fatigue, malaise, asthenia, ataxia. Musculoskeletal and connective tissue disorders: Tremors, arthralgia, pain in extremity. Nervous system disorders: Headache, lightheadedness, dizziness, paraesthesia. Psychiatric disorders: Insomnia, somnolence, confusion, depression, nervousness. Respiratory, thoracic and mediastinal disorders: Dyspnoea. Skin and subcutaneous tissue disorders: Acne, rash. Vascular disorders: Flushing, hypotension.
This drug may cause blurred vision, confusion, and fatigue, if affected, do not drive or operate machinery.
Evaluate cardiac status (e.g. ECG, 24-48 hours Holter monitoring, echocardiography) before starting and periodically during treatment. Monitor and correct electrolyte disturbances prior to treatment initiation. Routinely check LFTs and blood pressure during treatment.
Symptoms: Paraesthesia, confusion, hallucination, drowsiness, seizure; nausea; sinus bradycardia, hypotension, CV collapse, and cardiac arrest (in extreme cases). Management: Supportive and symptomatic treatment. Give IV atropine to treat bradycardia with hypotension. Administer benzodiazepines for seizures.
Increased exposure and risk of toxic effects with inhibitors of CYP1A2 (e.g. ciprofloxacin, fluvoxamine) or CYP2D6 (e.g. propafenone, quinidine). Decreased plasma concentrations with inducers of CYP1A2 (e.g. omeprazole) or CYP2D6 (e.g. phenytoin, rifampicin, phenobarbital). May increase, decrease, or unchange the plasma concentrations with cimetidine. May increase the plasma concentrations of caffeine and theophylline. Potentially Fatal: Increased risk of torsades de pointes with class Ia (e.g. procainamide, disopyramide), class Ic (e.g. flecainide, propafenone), and class III antiarrhythmics (e.g. amiodarone, sotalol).
May decrease the rate but not the extent of absorption with food. Avoid dietary changes which may markedly alter the urinary pH as it may increase or decrease the excretion of mexiletine.
Description: Mexiletine, a class 1B antiarrhythmic agent structurally similar to lidocaine, acts as a Na channel blocker by decreasing the rate of depolarisation of phase 0 of the action potential. It also increases the effective refractory period (ERP)/action potential duration (APD) ratio. Onset: 30-120 minutes (loading dose regimen). Pharmacokinetics: Absorption: Rapidly and almost completely absorbed from the gastrointestinal tract. Bioavailability: Approx 90%. Time to peak plasma concentration: 2-3 hours. Distribution: Widely and rapidly distributed in the body. Crosses the placenta and enters breast milk. Volume of distribution: 5-9 L/kg. Plasma protein binding: Approx 50-70%. Metabolism: Metabolised in the liver primarily by CYP2D6 and to a lesser extent by CYP1A2 isoenzyme into inactive metabolites (approx 90%) and major metabolites (e.g. p-hydroxymexiletine, hydroxy-methylmexiletine, and N-hydroxy-mexiletine). Excretion: Via urine (10% as unchanged drug). Increased excretion with urinary acidification. Elimination half-life: Approx 10-12 hours.
C01BB02 - mexiletine ; Belongs to class Ib antiarrhythmics.
Anon. Mexiletine. AHFS Clinical Drug Information [online]. Bethesda, MD. American Society of Health-System Pharmacists, Inc. https://www.ahfscdi.com. Accessed 15/09/2020.Anon. Mexiletine. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 15/09/2020.Buckingham R (ed). Mexiletine. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 15/09/2020.Joint Formulary Committee. Mexiletine. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 15/09/2020.Mexiletine Hydrochloride Capsule (Lannett Company, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 15/09/2020.Namuscla 167 mg Hard Capsules (Lupin Europe GmbH). European Medicines Agency [online]. Accessed 15/10/2020.