Sodium Channel Blockers – Oral Antiarrhythmic drugs

Dimitris Papadopoulos MD Fellow Of Interventional Pain Practice (FIPP)

Updated 30 December, 2010

Intravenous lidocaine has strong sodium-channel blocking properties and is effective in the treatment of neuropathic pain, as shown by non-controlled studies.

Antiarrhythmic drugs with local anaesthetic properties are sometimes used in the treatment of resistant neuropathic pain. In the  same way they stop the premature cardiac muscle fibre contraction, they also reduce ectopic discharges of injured nerves limiting pain stimuli transmitted to the brain.

The only antiarrhytmic drugs taken orally for the treatment of chronic pain syndromes are mexiletine (Mexitil) and flecainide (Tambocor). They are used in cases of post-stroke chronic pain, nerve injury, neuropathic pain of central aetiology, the complex regional pain syndrome, sympathetic dysfunction and peripheral diabetic neuropathy.

Mexiletine is chemically the same substance as lidocaine and is frequently used by dentists as local anaesthetic. Common side-effects that may occur are dizziness, gait instability, nausea and vomiting. The overall daily dose can be taken in three postprandial doses, to avoid stomach irritation. More rare side-effects are sore throat, headache, mental confusion, blurred vision, constipation, diarrhea, numbness and paraesthesia in upper and lower extremities. Overdosing may induce serious adverse events, including spasms, thoracic pain, heart and respiratory disorder, even cardiac arrest.

Flecainide is a drug approved for the treatment of cardiac arrhythmia achieving bradycardia. However, it is also administered to treat neuropathic pain. Although potential side-effects are rare, should they occur they are detrimental. For this reason its use should be avoided by patients suffering from cardiovascular disorders. Common side-effects  occurring during the 2-4 first weeks are nausea, dizziness, constipation, oedema and tremor.