What medications should be avoided in patients with Myotonia Congenita (a genetic muscle disorder)?

From the Guidelines

Patients with Myotonia Congenita should avoid medications that can exacerbate muscle stiffness and myotonic symptoms, including sodium channel blockers, potassium-sparing diuretics, depolarizing muscle relaxants, and beta-blockers. These medications can worsen symptoms by disrupting ion channel function or muscle excitability in patients with abnormal chloride or sodium ion channels in muscle cell membranes. When considering the management of patients with Myotonia Congenita, it is essential to tailor treatment decisions to the unique clinical circumstances of each patient, taking into account any coexisting conditions, as suggested by the American Heart Association 1. Key medications to avoid include:

• Sodium channel blockers such as mexiletine, phenytoin, and procainamide
• Potassium-sparing diuretics like spironolactone
• Depolarizing muscle relaxants such as succinylcholine
• Beta-blockers including propranolol and metoprolol Additionally, statins (like simvastatin and atorvastatin) should be used cautiously, and cold medications containing pseudoephedrine and other sympathomimetics should be avoided. It is crucial for patients to inform their anesthesiologist about their condition before surgery, as certain anesthetics require special consideration. Monitoring potassium intake is also vital, as both high and low levels can trigger symptoms in different types of myotonia congenita. Consultation with a neurologist experienced in neuromuscular disorders is recommended before starting or stopping any medication.

From the Research

Medications to Avoid in Myotonia Congenita

• Suxamethonium, as it can cause life-threatening muscle spasms and secondary ventilation difficulties in patients with Myotonia Congenita 2
• Tocainide, due to the risk of hematologic problems 3

Medications that May be Beneficial

• Lamotrigine, a sodium channel blocker that has been shown to effectively reduce myotonia in patients with non-dystrophic myotonias, including Myotonia Congenita 4
• Mexiletine, which has been found to be a potent antimyotonic agent and can reduce the severity of myotonia in patients with Myotonia Congenita 3, 5
• Imipramine and clomipramine, which have been shown to have a short-term beneficial effect on myotonia in small studies 6
• Taurine, which has been found to have a long-term beneficial effect on myotonia in small studies 6

Considerations for Treatment

• The benefits of myotonia control with pharmacological agents must be weighed against the risk of therapy in the individual patient 3
• The frequency and severity of side effects should be considered when selecting a medication for treatment 4, 6