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Anticonvulsants for Pain

Anticonvulsant (anti-epileptic) drugs are another group of drugs that are commonly used in the management of Pain, but which are primarily designed for other conditions.  They work by decreasing the excitability of nerves which may be firing too much, either due to stimulation or on their own, resulting in pain.  Essentially, what happens in this situation is that the nerves are often developing their own epileptic type activity and it is for this reason that the antiepileptics can be helpful.

The drugs in this class work on different chemical parts of the nervous system, and have varying benefits in pain – ones which work best for pain tend to be those affecting the flow of electrically charged sodium and calcium ions in and out of the nerve.  (For more details on this see the “How do we feel pain?”  section). 

Among the anticonvulsants which are often used for pain are older ones such as carbamazepine and sodium valproate, and newer ones such as gabapentin and pregabalin, though a number of other drugs are also used.  For more details see the medical professionals’ page  on this topic.

Sometimes combinations of different anticonvulsants or combinations with antidepressants or other drugs may be useful for difficult pains: this allows combinations of different mechanisms of action to be used.

Unlike antidepressants, which give benefit often at tiny doses, anticonvulsants generally need to be taken at their full dose for benefit for pain, though we would always still advise to "start low and go slow" with their doses since this may help to limit side effects. 

They are not addictive, though we would advise that if you are taking more than a tiny dose you make a stepwise reduction in their dose before stopping.  You shoud discuss this with your consultant or GP.  We are finalising a recommended guideline for the review and possible reduction of anticonvulsants which will be posted via the medical professionals' page on this topic.

The Faculty of Pain Medicine of the Royal College of Anaesthetists has recently produced information sheets for patients, that you may find helpful, on gabapentin and pregabalin.

For the overall pathway that is suggested for nerve pain treatment, and how the anticonvulsants fit into this, follow this link.  The British Pain Society / Map of Medicine Neuropathic Pain pathway will also give useful information.

Side effects

Unfortunately the chemical messengers involved in Pain also have effects at various other parts of the brain and nervous system (this is a problem for all drugs working on pain) and so side effects are often a problem; certain side effects are common to all of the anticonvulsant drugs.  These include dizziness, sedation, unsteadiness, nausea, weight gain and ankle swelling, and feeling “spaced out”. 

These side effects can be minimised by starting at a low dose and then slowly increasing, and if necessary stopping at a lower dose for a while before continuing to increase. 

As anticonvulsants do have side effects which may alter your ability to drive, you should not drive when you first take them.  You should wait and see what effect the drug has on you before driving.  Like almost all drugs acting on the central nervous system, anticonvulsants can also interact with alcohol, so you need to be cautious about this.  These drugs can have other side effects, which are listed in the data sheet which comes with the medications.  Extremely rarely, in some patients, gabapentin or pregabalin can be associated with decreased mood and sometimes suicidal thoughts.  If this happens it should be discussed with your doctor.

Some anticonvulsants could make the oral contraceptive pill less effective, so you should discuss this with your doctor and consider using other forms of birth control.

 

 Links

Gloucestershire Joint Formulary website

  

 

 

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Pain Service Website, Gloucestershire Hospitals NHS Foundation Trust
Webmaster Dr J G de Courcy, Consultant in Pain Medicine and Anaesthesia
email: pain.webmaster[at]glos.nhs.uk

Page updated 22/6/2016