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Lactation Safety Information

Anti-arrhythmic with suitable action
Unlicensed in the UK
Small amounts in breast milk
Limited published evidence of safety
Monitor infant for adverse effects and/or plasma levels
28th September 2016

New Medicines

Namuscla · Myotonic disorders in adults


New formulation

Development and Regulatory status

Phase III Clinical Trials
January 2019
Jan 19 · Launched in UK. List price: 100 capsule pack = £5000. Hospitals are advised to contact the manufacturer for pricing arrangements [7].
Dec 18 · Approved in the EU [6].
Oct 18 · Recommended for EU approval by CHMP - the full indication is "symptomatic treatment of myotonia in adult patients with non-dystrophic myotonic disorders.” It is proposed that Namuscla be prescribed by physicians experienced in the treatment of non-dystrophic myotonic disorders [5].
Sep 17 · Filed in EU via centralised procedure. Has orphan drug status [4].


Works by blocking ion channels for sodium ions in muscle cells. These sodium channels play a role in the contraction and relaxation of muscles and by blocking them, the medicine helps to reduce the rate of contractions as well as the stiffness that occur
Non-dystrophic myotonias are skeletal muscle ion channel disorders traditionally considered to be distinct from myotonic dystrophy because of the absence of progressive weakness and systemic features [1]. Prevalence is less than 1 per 100,000 people [2].
Myotonic disorders in adults

Further information

December 2020

Trial or other data

Mar 11 · PIII study (NCT00832000) completes [3].
Dec 08 · PIII study (NCT00832000) to determine the effectiveness of mexiletine 200mg three times daily in treating people with NDM starts. 59 patients aged 16 years or older will be recruited in the US, Canada, Italy and the UK. Primary outcome is patient-reported stiffness; collection of these data is due to complete Mar 11 [3].

Evidence based evaluations