Drug Action
Mexiletine is a sodium channel blocker which reduces the delay of muscle relaxation thereby decreasing muscle stiffness.
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Drug reference
Mexiletine is a sodium channel blocker which reduces the delay of muscle relaxation thereby decreasing muscle stiffness.
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Myotonia in non-dystrophic myotonic disorders ▶BY MOUTH ▶Adult: 167 mg once daily for at least 1 week, then increased if necessary to 333 mg daily in divided doses for at least 1 week, then increased if necessary to 500 mg daily in divided doses; maintenance 167–500 mg daily; maximum 500 mg per day
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Abnormal Q-waves. atrial tachyarrhythmia, fibrillation or flutter. complete heart block or any heart block susceptible to evolve to complete heart block. heart failure (with ejection fraction less than 50%). history of myocardial infarction. sinus node dysfunction. symptomatic coronary artery disease. ventricular tachyarrhythmia
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Cardiac disorders other than those contra- indicated. epilepsy (increased risk of seizures)
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Manufacturer advises avoid if hypersensitivity to any local anaesthetic.
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The manufacturer of Namuscla ® has provided a Guide for Healthcare Professionals.
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Scottish Medicines Consortium (SMC) decisions SMC No. SMC2241 The Scottish Medicines Consortium has advised (March 2020) that mexiletine (Namuscla ®) is not recommended for use within NHS Scotland for the symptomatic treatment of myotonia in adults with non-dystrophic myotonic disorders, as the economic case was not demonstrated.
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→Appendix 1: mexiletine
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▶Common or very common Abdominal pain. arrhythmias. asthenia. chest discomfort. drowsiness. headache. hypotension. insomnia. malaise. nausea. pain in extremity. paraesthesia. skin reactions. vasodilation. vertigo. vision disorders ▶Uncommon Seizure. speech disorder ▶Rare or very rare Hepatic disorders. severe cutaneous Musculoskeletal system adverse reactions (SCARs) ▶Frequency not known Atrioventricular block. circulatory collapse. confusion. diarrhoea. gastrointestinal disorders . hallucination. leucopenia. lupus-like syndrome. pulmonary fibrosis. taste altered. thrombocytopenia. vomiting SIDE-EFFECTS, FURTHER INFORMATION Manufacturer advises evaluation and correction of electrolytes prior to therapy initiation, with monitoring continued throughout treatment with mexiletine, due to possible proarrhythmic effects.
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Manufacturer advises avoid—limited information available.
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Manufacturer advises avoid—present in human milk and insufficient information on the effects in infants.
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Manufacturer advises caution in mild or moderate impairment; avoid in severe impairment (limited information available). Dose adjustments Manufacturer advises any dose increase should only be made after at least 2 weeks of treatment in mild or moderate impairment.
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Manufacturer advises avoid in severe impairment (limited information available).
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▶Manufacturer advises cardiac evaluation before starting treatment, within 48 hours of starting treatment, and during treatment (consult product literature). ▶Manufacturer advises monitor electrolytes before starting treatment and during treatment—imbalances should be corrected.
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Manufacturer advises capsules should be swallowed whole with water, while in an upright position. If digestive intolerance occurs, capsules should be taken during a meal.
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There can be variation in the licensing of different medicines containing the same drug. Capsule ▶Namuscla (Lupin Healthcare (UK) Ltd) Mexiletine (as Mexiletine hydrochloride) 167 mg Namuscla 167mg capsules | 100 capsule P £5,000.00 DT = £5,000.00 Musculoskeletal system 3.4 Nocturnal leg cramps Nocturnal leg cramps Quinine salts Quinine salts p. 655, such as quinine sulfate are effective in reducing the frequency of nocturnal leg cramps by about 25% in ambulatory patients; however, because of potential toxicity, quinine is not recommended for routine treatment and should not be used unless cramps cause regular disruption to sleep. Quinine should only be considered when cramps are very painful or frequent; when other treatable causes of cramp have been excluded; and when non- pharmacological treatments have not worked (e.g. passive stretching exercises). It may take up to 4 weeks for improvement to become apparent; if there is benefit, quinine treatment can be continued. Treatment should be interrupted at intervals of approximately 3 months to assess the need for further quinine treatment. In patients taking quinine long term, a trial discontinuation may be considered. Quinine is toxic in overdosage and accidental fatalities have occurred. 3.5 Spasticity Other drugs used for Spasticity Dantrolene sodium, p. 1417 . Diazepam, p. 360 CANNABINOIDS
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Manufacturer advises patients and carers should be informed about the presenting symptoms of arrhythmias (e.g. fainting, palpitation, chest pain, shortness of breath, light- headedness, lipothymia, and syncope) and advised to seek immediate medical attention if symptoms develop. Alert card An alert card should be provided. Driving and skilled tasks Manufacturer advises patients and carers should be counselled on the effects on driving and performance of skilled tasks—increased risk of fatigue, confusion, and blurred vision.
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167 mg once daily for at least 1 week, then
First-line fragment. Read the complete Indications and Dose section above.
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