Neuropathic pain drug therapy

The mechanisms of pain and the ability to control pain may vary in different pain states. This is of particular importance in consideration of a rational basis for the treatment of both inflammatory and neuropathic pain where the damage to tissue and nerve leads to alterations in both the peripheral and central mechanisms of pain signalling. In respect of existing drug therapies, this plasticity, the ability of the system to change in the face of a particular pain syndrome, explains the effectiveness of NSAIDs in inflammatory conditions and yet is also responsible for some of the limitations in the effectiveness of opioids in neuropathic pain. 

There are two major classes of pain medications, nonopioids and opioids. The nonopioids used to treat mild pain include agents such as acetaminophen, both steroid and nonsteroidal antiinflammatory drugs (NSAIDs), and acetylsalicylic acid. Anticonvulsants suppress neuronal firing and are also helpful in neuropathic pain. Antiinflammatory agents (e.g., NSAIDs or corticosteroids) may be particularly helpful when bony involvement occurs and are often used for low-intensity pain. Steroids decrease inflammatory edema and are useful in cases of nerve and spinal cord compression, lymphedema, visceral pain caused by organ enlargement, and bone pain. Finally, short-term corticosteroid therapy may also produce euphoria (thus ameliorating less severe depressions) as well as reverse anorexia. 

Tremont-Lukats, I. W., Megeff, C., Backonja, M. M. Anticonvulsants for neuropathic pain syndromes mechanisms of action and place in therapy, Drugs 2000, 60, 1029-1059. 

II. Drug Therapy of Neuropathic Pain—Effectiveness of Narcotic Analgesics HI. Alternative Neural Changes in Morphine-Resistant Neuropathic Pain States IV. New Drug Therapy for Neuropathic Pain V. Conclusion References... 

II. Drug Therapy of Neuropathic Pain —Effectiveness of Narcotic Analgesics... 

Spasticity is a central feature of multiple sclerosis (MS) and spinal cord injury (SCI). It consists of a velocity-dependent increase in tonic stretch reflexes with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex as one component of the upper motor syndrome (Young 1994). Existing drug therapy is far from satisfactory in terms of efficacy and unwanted effects (Panegyres 1992). Tremor, ataxia and lower urinary tract symptoms are frequently troublesome in MS. Both neuropathic and nociceptive pain (dealt with in Sect. 2.3) are also common in MS and SCI, and dozens of very painful muscle spasms can occur each day. Small wonder that there is also a high incidence of anxiety and depression in these conditions. 

Ferrer-Brechner T (1989) Anesthetic techniques for the management of cancer pain. Cancer 63 [Suppl ll] 2343-2347 Filshie J (1988) The non-drug treatment of neuralgic and neuropathic pain of malignancy. Cancer Surv 7 161-193 Fiore D et al (1985) Upper abdominal pain therapy by CT-guided alcohol block of the celiac-splanchnic region. Rays 10 43-48... 

Sativex has generally been found to be more effective than the currently approved cannabinoid drugs in the management of pain. It has been reported to be useful in chronic non-malignancy pain, intractable cancer pain, and peripheral and central neuropathic pain, including that related to MS. It has already been approved in Canada for the treatment of cancer pain refractory to opioid therapy and central neuropathic pain in MS. Studies have shown it to help patients with brachial plexus root avulsion and rheumatoid arthritis. 

Observational studies The usefulness of gabapentin in combination with opioids in 24 Japanese patients with neuropathic cancer pain has been assessed in an open prospective study [155 ]. Gabapentin was added to opioid therapy in an initial dose of 200 mg/day titrated to a maximum dose of 2400 mg/day over 15 days. Gabapentin reduced the score on a pain scale, but the reduction was of minimal clinical benefit. Four patients withdrew because of adverse events headache, myoclonus, heartburn, and an attack of bronchial asthma). Only a few patients reported somnolence or dizziness, and these symptoms did not require drug withdrawal. 

Identification of the populations at risk patients on long-term opioid therapy for various chronic pain situations (musculoskeletal, neuropathic, sickle cell disease, HIV-related disease, and palliative care), drug abusers, recovering addicts in opioid maintenance programs. 

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