Gabapentin in pain management.

G abapentin [1-(aminomethyl)cyclohexane acetic acid] is a structural analog of g-aminobutyric acid (GABA), which was initially introduced in 1994 as an antiepileptic drug (AED), particularly for partial seizures. For a long time, AEDs such as carbamazepine have been recognized as adjunctive drugs for treating certain symptoms of chronic pain syndromes. It is then not surprising that gabapentin was soon found to be promising in treating neuropathic pain associated with postherpetic neuralgia (PHN) (1,2), postpoliomyelitis neuropathy (3), and reflex sympathetic dystrophy (4). Placebo-controlled clinical trials also have indicated a role of gabapentin in treating pain related to diabetic neuropathy (DNP) (5) and PHN (6). A number of animal studies have investigated the effect of gabapentin on signs of neuropathic pain, such as hyperalgesia and allodynia. Data derived from these studies are generally in agreement with clinical observations. More recently, studies on animal models of acute pain have indicated a role of gabapentin in ameliorating pain from incisional injury and arthritis (7,8), implicating even broader use of gabapentin in treating a variety of pain states. Indeed, it is a common experience that gabapentin has been increasingly prescribed by pain specialists, neurologists, primary care physicians, and other physicians for cases in which pain of nonnociceptive origin is suspected. The clinical impression that there are fewer side effects of gabapentin often becomes part of the rationale for initiating gabapentin therapy. However, both the efficacy and indications of gabapentin for pain treatment are yet to be established, and there is a lack of consensus with regard to the dosage, indications for use of gabapentin, and clinical outcome data. In this article, three lines of evidence will be examined regarding the role of gabapentin in pain treatment: 1) clinical evidence (case reports and trials) for a role of gabapentin in pain treatment will be discussed with an attempt to identify pain symptoms that are likely to be responsive to gabapentin; 2) animal studies of gabapentin on neuropathic pain and other pain behaviors will be evaluated; and 3) possible mechanisms of gabapentin actions will be considered in relation to mechanisms of neuropathic pain in particular. Finally, clinical issues of gabapentin treatment will be discussed in the context of its role in neuropathic pain relief.