Lidocaine Patches and PHN

Postherpetic neuralgia is a complication of shingles, which occurs when the virus that causes chicken pox remains in the body, dormant in nerve cells. Shingles manifests as rash and blisters accompanied by pain, but sometimes the pain remains even after the skin condition has disappeared. This is postherpetic neuralgia. Although there are a number of treatments, including steroids, painkillers, and even antidepressants, lidocaine skin patches offer one easy-to-use alternative with (usually) no side effects.

In a 1999 blind study conducted by the Education and Research in Pain Medicine and Palliative Care (Beth Israel Medical Centre, New York), researchers found that 78% of the subjects preferred the lidocaine patch treatment over that of a placebo. Simply put, lidocaine patches are small patches (much like band-aids) that contain lidocaine, which can be applied directly to the skin to numb the areas experiencing pain.

Dermaflex and Lidoderm are two leading providers of lidocaine patches, with Dermaflex offering 2% lidocaine patches and Lidoderm offering 5%. Although PHN can be treated as effectively with pills (taken orally), which are absorbed internally, the patch has the positive feature of not requiring an increase in dosage. Another positive aspect of the patch is that it requires less attention: a patient can wear up to three patches at a time, for twelve hours without interruption (followed by twelve hours without the patch). Additionally, because the patch is not absorbed internally but through the skin, it carries an even smaller risk of interacting negatively with other medications. Side effects are minimal and rare; they include: Mild redness, swelling, burning, blisters, bruising, irritation, change in skin color, or numbness at the application site. Risk of cardiac arrest is increased for those on antiarrhythmic medications. Of course, if you experience any effects more serious than these (confusion, dizziness, allergic reaction), consult your doctor immediately.

On the other hand, the negative aspect of the treatment is that the patch needs to cover the skin where there is pain. If the region of pain is larger than the patch, it can still be effective (assuming size difference is not extreme and the lidocaine is applied to the most painful region), but the patch cannot be worn on the face, and many patients find it inconvenient to use the patch if the affected skin is not under clothing.

Lidocaine works by blocking sodium channels in the neuron (nerve cell) cell membrane. These sodium channels are responsible for nerve signal movement among nerve cells, and when blocked, the sodium cannot move in and out of the cell to amplify the sensory signals as they travel through the body. Thus, the action potential of the nerves is decreased and the lidocaine produces anaesthetic effects. The lidocaine patch, because it focuses the area being treated, can selectively treat postherpetic neuralgia.