Most of the anticonvulsants affect nerves by changing the way ions (potassium, sodium, calcium) work on the membranes of the nerves to chemically induce a signal.
(Some cardiac drugs like Mexetil, and Tambocor also affect membrane potentials, but have little if any antiseizure effects)

This is an explanation of how this works:
http://en.wikipedia.org/wiki/Voltage-gated_ion_channel

Historically anti-seizure drugs were found to affect pain perception over time postmarketing. The first was Tegretol, which was initially used for trigeminal neuralgia. It was never a first line drug for seizures, because it has some long term toxic effects. But over time Dilantin was used for cardiac conduction problems the same way.

I would encourage anyone here taking an anti-seizure drug to look it up on www.rxlist.com and read the precautions and side effects carefully. I won't be going into detail here because of space considerations.

All of the anti-seizure drugs are slightly different in the way they work for chronic pain. Here is a good overview of the subject:
http://pain.about.com/od/treatment/a...onvulsants.htm

Some of them are more commonly used for PN, and I think that is based on some studies that various drug companies have done, or that doctors have seen in their CME classes. (continuing medical education for relicensure).

All of the anti-seizure medications typically have long term potentially serious side effects. So I will point those out, in case your doctor is not monitoring you closely.

Tegretol/Trileptal have potential to cause a sodium imbalance
which is called hyponatremia and lowering of white cells.
http://en.wikipedia.org/wiki/Carbamazepine
Trileptal was designed to have fewer liver metabolic complications, but Tegretol interacts with many other drugs' metabolism in the body. A good drug checker to test your specific combinations can be found here:
http://www.drugs.com/drug_interactions.html
As you can see there are MANY potentials for getting into difficulties taking Tegretol!

Topamax is another often used to prevent migraine.
It can also be used for chronic pain management and sometimes helps to lower the need for opiates. It too, has many serious potentially damaging qualities. Doctors were sent warning letters over the years about them, but still today some do not test for bicarbonate depletion-- which leads to metabolic acidosis in about 30-40% of patients. Also kidney stones and glaucoma are possible. Typically Topamax is started at a low dose and slowly increased. Keeping at the lowest possible level is a very good idea. This drug does affect cognitive abilities and has been nicknamed Dopamax as a result. If your doctor is NOT monitoring you and you feel ill taking this, demand a test for bicarbonate levels.

The others listed at the About.com link all have potential to help. This seems to be very personally unique to individuals, and there is no way really to predict who will respond to which unless you try them.

The two cardiac drugs, Mexetil and Tambocor are used infrequently. Mexetil is sometimes called "oral Lidocaine" because it works on sodium channels. It is not commonly given unless patients don't respond to other drugs, because it can be very upsetting to the stomach, may cause ulceration, or damage to the esophagus. So staying upright after taking may minimize reflux and burning this causes. But many people discontinue it because of GI side effects.

Tambocor can be problematic mixed with other drugs:
http://en.wikipedia.org/wiki/Flecainide

So use the drug checker, to test out your combinations for your own safety. Some online or pharmacy databases may not have all of them listed equally, so checking yourself is important.
Both of these heart drugs have a narrow therapeutic index, meaning errors in administration, or taking too much can be dangerous or fatal. So strict adherence to directions is a MUST for them.

Here are some other links about using these medications for chronic pain. I found these interesting and they may be helpful for some here:

http://www.mayoclinic.com/health/pai...SECTIONGROUP=2

http://en.wikipedia.org/wiki/Sodium_channel_blocker

http://www.bayareapainmedical.com/sodiumchnlblk.html

http://www.cvpharmacology.com/antiar...m-blockers.htm

Many of the anti-seizure drugs interfere with nutrients in the body. Most commonly calcium, Vit D, and folate.
The newer ones like Lamictal, Zonegran, Keppra don't have studies yet on this. But often doctors lump them into the family category and you may be counseled to have a Vit D test, and or use a calcium supplement.

Valproate (Depakote), is rarely used for PN, but may be tried when others fail. It specifically blocks folic acid and carnitine.
It also is suspected of affecting zinc because it causes hair loss in some patients.
Tegretol can cause low folic acid too.

I have not run across anyone using Gabitril on this forum yet. I suspect the side effects for this limits its use.

Discontinuing these drugs suddenly can have serious consequences.
If you need to discontinue any of them, they should be tapered off carefully, with doctor supervision.

edit: A new article has appeared in Science News this week. 6-2012:
It discusses a specific sodium channel target in the peripheral nervous system to block pain:

http://www.sciencenews.org/view/feat...e/Hurt_Blocker

We may see drugs developed to target this area, eventually.