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    Has all of the relevant evidence been taken into account?
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    Are the summaries of clinical and and cost effectiveness reasonable interpretations of the evidence?
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    Are the recommendations sound and a suitable basis for guidance to the NHS?
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1 Recommendations

1.1 Mexiletine (Namuscla) is not recommended, within its marketing authorisation, for treating the symptoms of myotonia in adults with non-dystrophic myotonic disorders.

1.2 This guidance does not require that patients having treatment with mexiletine (Namuscla) that was started in the NHS through the interim agreement for use as a 'pass through' drug for patients within specialised neurosciences centres, which came into effect on 1st April 2019, should continue to receive treatment with Namuscla. Commissioners are not required to continue to fund that treatment. This is a departure from NICE's usual practice that negative guidance ought not to affect NHS treatment started before the guidance is published.

Why the committee made these recommendations

Treatments for the symptoms of myotonia in adults with non-dystrophic myotonic disorders already include imported mexiletine (that is not licensed in the UK). Other sodium channel blockers are used if mexiletine is not suitable. NICE's remit for this appraisal to appraise mexiletine (Namuscla) because it is the only product with a UK marketing authorisation.

Clinical trial evidence suggests that mexiletine is better than placebo at reducing the symptoms of myotonia. But the trial did not compare mexiletine with other sodium channel blockers and a higher dose of mexiletine was used in the clinical trial than people would normally have in the NHS.

The main problem with the economic model is that it does not compare mexiletine with other sodium channel blockers that are used in the NHS. The size of the clinical benefit is also uncertain. The cost-effectiveness estimates for mexiletine are much higher than what NICE considers a cost-effective use of NHS resources and would potentially be higher if compared with other sodium channel blockers rather than best supportive care. Therefore, mexiletine cannot be recommended.