March 12, 2010
   
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Pain Free: Modern Drugs and Neuropathic Pain
 

Dr. Fields is Professor of Neurology and Physiology, and Director, Wheeler Center for the Neurobiology of Addiction, University of California, San Francisco.

In the past three years, Dr. Fields has served as a consultant for Neurogen and Endo Pharmaceuticals, and has served on the Speakers' Bureau for Pfizer, Abbott and Merck.

During the last millenium, mankind made revolutionary advances in relieving pain. Treatment progressed from non-treatments, such as "biting the bullet," to alcohol and crude opium-based drugs, to the development of safe modern opioids, or narcotic-based painkillers, and a wide range of general and local anesthetics. At least in the developed world, most everyone has found pain relief, at one time or another, from one of these drugs.

Yet despite all our advances, there is one type of pain which, until recently, could not effectively be controlled by modern medicine — neuropathic pain.

Usually chronic and often devastating, neuropathic pain is the result of damage to the body's nervous system. The two most common causes are diabetes ("diabetic neuropathy") and herpes zoster ("postherpetic neuralgia" or "shingles"), an infection of the nerves by the same virus that causes chickenpox. Both cause excruciating pain.

What Does Neuropathic Pain Feel Like?
Although neuropathic pain is highly variable and is felt very differently by different people, doctors can easily distinguish it from other causes of pain. There is usually some abnormality of skin sensation in the painful area and sufferers usually describe neuropathic pain as strange, unfamiliar, often as a burning sensation. It can have a sharpness or a brief shooting quality, as well as a sensation that is described as tingling, crawling, electrical.

Frequently, there is a long delay between the actual nerve injury and the appearance of pain; in fact, it is not unusual for the pain to begin at about the time a person is beginning to recover physically.

Treating Neuropathic Pain
The main problem with treating neuropathic pain is that the standard array of non-narcotic analgesics [acetaminophen, aspirin, non-steroidal anti-inflammatory agents (NSAIDs and cyclooxygenase 2 inhibitors)] have little effect on neuropathic pain. Recently, however, several different classes of drugs have been developed that do help people suffering from neuropathic pain. These are:

Antidepressants

TCAs
Tricyclic antidepressant drugs, or TCAs, are the most extensively studied treatments for neuropathic pain.(22) The most commonly prescribed TCA is amitriptyline. While effective, this drug does have significant side effects,(17) including a type of low blood pressure called orthostatic hypotension. Other side effects include urinary retention, memory loss, heart problems and drowsiness. Because of these significant and potentially serious side effects, doctors normally start patients on a very low dose and increase the dosage slowly.

Desipramine, another TCA, appears to be almost as effective as amitriptyline in most studies,(13)(15) but with fewer side effects and significantly less drowsiness.

SSRIs
For most types of neuropathic pain, selective serotonin reuptake inhibitors (SSRIs) are significantly less effective than TCAs, although the SSRI, paroxetine, has been reported to help pain caused by diabetic neuropathy.(21) On the other hand, SSRIs have virtually none of the side effects of desipramine or amitriptyline, and are non-sedating, that is, they don't cause drowsiness. An added benefit of SSRIs is that they are very effective at treating the depression and anxiety that sometimes afflict those with chronic pain.

Newer Drugs
Though still under study, one of the newer generation antidepressants, venlafaxine (sold under the brand name Effexor®), is a promising drug for neuropathic pain control. Like the SSRIs, venlafaxine is safer than TCAs but acts in a similar way to TCAs and, thus, seems to be more effective than other SSRIs for pain relief.(12)(16)

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Readers Comments

Comment by: Salman Ahmed Thu., Feb. 11, 2010 at 10:54 am EST
Very informative site. Learned a lot about this disease and treatment options.


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