THERAPEUTICS

Brands

• Mexitil

Generic?

• Yes

Class

• Antiarrhythmic

Commonly Prescribed for

(FDA approved in bold)

• Ventricular arrhythmias

• Symptomatic myotonia (myotonia congenita, myotonic dystrophy)

• Intractable headache

• Trigeminal autonomic cephalalgia

How the Drug Works

• An oral analog of lidocaine. Class 1b antiarrhythmic agent that depresses phase 0; it reduces the rate of rise of the action potential (not the duration) by inhibiting the inward sodium current but not affecting resting membrane potential. It acts more on faster than slower heart rates. 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 in the heart

How Long Until It Works

• 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

If It Works

• Continue to use with appropriate monitoring

If It Doesn't Work

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

Best Augmenting Combos for Partial Response or Treatment-Resistance

• Myotonia: quinine and other AEDs are occasionally used. Phenytoin is also effective but has similar antiarrhythmic properties and may interact with mexiletine

Tests

• 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

ADVERSE EFFECTS (AEs)

How the Drug Causes AEs

• Drug effect blocking sodium channels

Notable AEs

• GI AEs (nausea, vomiting, heartburn) are most common. CNS AEs (tremor, nervousness, coordination difficulties, blurred vision, confusion) are much more common when serum levels exceed 2mcg/mL

Life-Threatening or Dangerous AEs

• New or worsening cardiac arrhythmias

• Acute hepatic injury (usually in the first few weeks of therapy)

• Blood dyscrasias, including leukopenia (rare)