Myotonia in non-dystrophic myotonic disorders

Active Ingredient: Mexiletine

Indication for Mexiletine

Population group: only children (1 year - 12 years old) , adolescents (12 years - 18 years old) , adults (18 years old or older)

Therapeutic intent: Curative procedure

Mexiletine is indicated for the symptomatic treatment of myotonia in children aged 6 to 11 years weighing at least 20 kg, adolescents aged 12 to 17 years and adult patients ≥18 years with non-dystrophic myotonic disorders.

For this indication, competent medicine agencies globally authorize below treatments:

167 mg once daily as starting dose for at least 1 week followed by 167 mg – 500 mg daily as maintenance treatment

For:

Dosage regimens

Oral, 167 milligrams mexiletine, once daily, over the duration of 1 week. Afterwards, oral, 333 milligrams mexiletine, divided 2 times daily, over the duration of 1 week. Afterwards, oral, 500 milligrams mexiletine, divided 3 times daily. The maximum allowed total dose is 500 milligrams mexiletine daily.

Detailed description

Before starting mexiletine treatment,

Detailed and careful cardiac evaluation should be carried out by cardiologist; throughout treatment with mexiletine, cardiac monitoring needs to be continued and adapted as a function of the heart condition of the patient.
Electrolytic evaluation should be done prior to initiating therapy with mexiletine in every patient and any electrolyte imbalance needs to be corrected before administering mexiletine.

The recommended starting dose of mexiletine is 167 mg daily. After at least 1 week of treatment, based on the clinical response, the daily dose can be increased to 333 mg daily. After at least 1 further week of treatment, based on clinical response, dose can be further increased to 500 mg daily.

Maintenance treatment is between 167 mg – 500 mg daily, according to the intensity of symptoms and the clinical response, taken regularly throughout the day as required.

The dose should not exceed 500 mg/day. Regular reassessment should be implemented: discontinue long-term treatment in a patient not responding or not experiencing benefit of the treatment.

Patients with cardiac disorders

In case of modification of the mexiletine dose, or if medicinal products susceptible to affect cardiac conduction are co-administered with mexiletine, patients should be closely monitored by ECG (especially patients with conduction anomalies).

Elderly

Experience with mexiletine in patients with myotonic disorders aged ≥65 years is limited. Based on the pharmacokinetic properties of mexiletine, no dose adjustment is required in patients aged 65 years and over.

62-167 mg once daily as starting dose for at least 1 week, followed by 62-500 mg daily as maintenance treatment, based on body weight

For:

Dosage regimens

Regimen A, in the case that patient weight is ≥ 20 kg and patient weight is < 30 kg :

Oral, 62 milligrams mexiletine, once daily, over the duration of 1 week. Afterwards, oral, 62 milligrams mexiletine, 2 times daily, over the duration of 1 week. Afterwards, oral, 62 milligrams mexiletine, 3 times daily.

Regimen B, in the case that patient weight is ≥ 30 kg and patient weight is < 40 kg :

Oral, 83 milligrams mexiletine, once daily, over the duration of 1 week. Afterwards, oral, 83 milligrams mexiletine, 2 times daily, over the duration of 1 week. Afterwards, oral, 83 milligrams mexiletine, 3 times daily.

Regimen C, in the case that patient weight is ≥ 40 kg and patient weight is < 60 kg :

Oral, 124 milligrams mexiletine, once daily, over the duration of 1 week. Afterwards, oral, 124 milligrams mexiletine, 2 times daily, over the duration of 1 week. Afterwards, oral, 124 milligrams mexiletine, 3 times daily.

Regimen D, in the case that patient weight is ≥ 60 kg :

Oral, 167 milligrams mexiletine, once daily, over the duration of 1 week. Afterwards, oral, 167 milligrams mexiletine, 2 times daily, over the duration of 1 week. Afterwards, oral, 167 milligrams mexiletine, 3 times daily.

Detailed description

Before starting mexiletine treatment,

Detailed and careful cardiac evaluation should be carried out by cardiologist; throughout treatment with mexiletine, cardiac monitoring needs to be continued and adapted as a function of the heart condition of the patient.
Electrolytic evaluation should be done prior to initiating therapy with mexiletine in every patient and any electrolyte imbalance needs to be corrected before administering mexiletine.

Children and adolescents (from 6 to 17 years of age)

In paediatric patients, the recommended dose is dependent on body weight:

Recommended doses in paediatric patients:

Body weight (kg)	Once daily (morning)	Twice daily (morning and evening)	Three times daily (morning, afternoon and evening)	Maximum total dailydose
20-30 kg	62 mg	124 mg	186 mg	≈187 mg/day
30-40 kg	83 mg	166 mg	249 mg	≈250 mg/day
30-40 kg	83 mg	166 mg	Alternative: 248 mg	≈250 mg/day
40-60 kg	124 mg	248 mg	372 mg	≈375 mg/day
≥60 kg	167 mg	334 mg	501 mg	500 mg/day

Active ingredient

Mexiletine
Mexiletine blocks sodium channels with a stronger potency in situations of excessive burst of action potentials (use-dependent block) and/or prolonged depolarization (voltage-dependent block), as occurring in diseased tissues, rather than on physiological excitability (resting or tonic block). Mexiletine is, therefore, mostly active on muscle fibres subject to repeated discharges (such as skeletal muscles). It improves myotonic symptoms by decreasing muscle stiffness through reduction of the delay of muscle relaxation. Read more about Mexiletine

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