Clinical research study into the effectiveness of mexiletine on non-dystrophic myotonia

11 August 2011
Project Leaders. Dr. Gea Drost, neurologist and Prof. dr. Gert Jan van der Wilt, epidemiologist, UMC St. Radboud, Nijmegen

Request.

At the end of November 2010, dr. Drost approached Cinderella with the request to be helpful in acquiring Mexiletin for the treatment of patients with non-dystrophic myotonias (NDM). Mexiletin is normally prescribed to patients with cardiac arrhythmias and neuropathic pain and might also be effective in patients with NDM. This group of genetic disorders is caused by a specific ion channel defect, selective for sodium or chloride, in skeleton muscles. This leads to a distortion of muscle relaxation, which can be experienced by the patient as a very painful muscle stiffness and even can cause accidents.
The most frequently occurring disease within the NDM family, myotonia congenita, presents itself as a dominant genetic disorder (Thomsen’s disease) or as a recessive disease (Becker ‘s disease). The prevalence of Thomsen’s disease is 1: 400,000, of Becker’s disease 1: 25.000. Treatment is only indicated if the muscle stiffness interferes with daily activities. The evidence that Mexiletin might be effective in the treatment of NDM is based on case reports and small uncontrolled studies.
To scientifically demonstrate the effectiveness of Mexiletin for the treatment of NDM, Drost et al. have planned to initiate a multicentre European study. Based on earlier small studies the preferred dosage would be 3 x 200 mg Mexitelin per day. However, it appeared that Mexiletin is no longer available in the Netherlands as, for inimitable reasons, producer Boehringer Ingelheim recently has decided to stop the supply. Mexiletin is also expensive and non-refundable by health insurance companies for the indication congenital myotonia , because of its ‘unproven effectiveness’ (see: report by the Commission Pharmaceutical Aid 2011 of the College for Health Insurances).
Accomplishments of Cinderella. After some search work and enabling its network in the USA, Cinderella discovered that Mexiletin is available via regular channels in the US and Canada. The pharmacy of the University Medical Center Nijmegen was therefore advised to just ordering Mexiletin in Canada at TEVA Pharmaceuticals.
However, the pharmacy of the UMC could not manage to get from TEVA the essential information about the dosage of Mexitelin capsules, so that the expertise of Cinderella was invoked again. After renewed contact between Cinderella and TEVA in August 2011 it was found that Mexiletin capsules, containing the required preference dosage of 200 mg to be used in the clinical trial, were no longer available. Only capsules in dosages of 150 and 250 mg could be delivered . To meet the desired daily dose of 600 mg, project leader Drost therefore is obliged to prescribe her trial patients 4 times per day a capsule of 150 mg Mexitelin. On the progress of the European study Cinderella will report in due time.
Comments by Cinderella.

NDM is a group of rare and heterogeneous conditions that invalidate part of the patients physically as well as socially. The treatment is ambiguous. In various publications of clinical research Mexiletin is the drug of first choice. The drug complies to one of the two criteria that Cinderella adheres to for adoption as a stepchild: promising. Also the other criterion (feasibility) is met: physicians may prescribe off-label and unregistered drugs if they believe that this is the best option for their patient.
As a result of the small number of patients with NDM it is not clear how effective treatment with Mexiletin will be in terms of response rate, quality of the response and long term effects. That is the conclusion of Drost and her colleagues in their Cochrane Review and on the basis of their own experiences. Their initiative to investigate this scientifically deserves every support. It is irrational that the Commission Pharmaceutical Aid does not support but rather hinders this initiative, by advising health insurers not to reimburse Mexiletin. However, this need not to obstruct the investigation. There are health insurance companies that reimburse interventions for which all rational pharmacotherapy is missing.
Cinderella hopes that her efforts for this project will contribute to a better treatment of patients with non-dystrophic myotonias.

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