(FDA approved in bold)

• Cardiac arrhythmias
  
• Symptomatic myotonia (myotonia congenita, myotonic dystrophy)
  
• Pain in peripheral neuropathy
  
• Intractable headache

• Class 1B antiarrhythmic agent that depresses phase 0 (reduces the rate of rise of the action potential). An oral analogue of lidocaine. It has actions on surfaces and membranes of skeletal muscle and neuronal sodium-channel blocking properties. It also reduces the effective refractory period in Purkinje fibers

• Antiarrhythmic effect will occur within hours, although it may take time to find optimal dose. May take more time (days or weeks) to see relief and determine most effective dose in myotonia or pain disorders

• Continue to use with appropriate monitoring

• Check serum levels and if not effective change to an alternative agent

• Myotonia: Quinine and other anticonvulsants are occasionally used. Phenytoin is also effective but has similar antiarrhythmic properties and may interact with mexiletine
  
• Neuropathic pain: other anticonvulsants and antidepressants can be used

• Monitor hepatic enzymes and CBC during therapy. Obtain ECG at baseline and for any new symptoms. Check a serum mexiletine level to guide therapy and for any AEs