Gabapentin (Neurontin)是用於治療seizure disorder (癲癇)、神經病變引起的疼痛(neuropathic pain、post-herpetic pain等)、major depressive disorder (憂鬱症)等的藥物。劑量通常是300 mg，一天四次左右。它是GABA之類，抑制腦細胞間聯繫(synaptic impulse)的化合物質。(下面引用的文章是討論長效型藥物，新批准使用於restless leg syndrome=RLS，服用法不一樣)
Gabapentin還有改善皮膚刺癢(paresthesia-dysesthesia，俗稱pins-and-needles)症狀的作用。劑量不必要高，100-200 mg，一天兩三次就可能有效。這是少有人討論的藥效，不過，對有此症狀的病患是很重要。
皮膚刺癢是真性多血症(polycythemia vera，PV)病患常見(40%)的症狀。因為這是非致命的症狀，很少研究。但是症狀非常惱人，可以使病人極為難受，無法工作、無法入眠。因為PV病人不知道 "刺癢" 和 "癢" 不一樣，常常稱為是皮膚癢(pruritus)，而使用antihistamine治療(無效) [我相信教科書上描寫PV的皮膚症狀為 pruritus是錯誤，應該是paresthesia-dysesthesia。兩者發生機轉不一樣: Paresthesia-dysesthesia是neuropathic pain的一種，撫擦皮膚就會舒服。Pruritus的機轉尚不明，有可能是和pain不同的神經傳導，會引起反射性搔抓，一般使用antihistamine可以抑制pruritus]。
真性多血症的皮膚刺癢一般典型的是熱水澡之後出現，不過很有可能開始時是由某些食物刺激引起(food intolerance: http://tw.myblog.yahoo.com/ccshsu-clement/article?mid=5982)，以後PV病情可能有某些變化，而成為常態性症狀。[這是筆者的疾病自身觀察的結果，因此會有後續情報。]
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April 11, 2011 — The US Food and Drug Administration (FDA) has approved gabapentin enacarbil extended-release tablets (Horizant; GlaxoSmithKline and XenoPort Inc) for the treatment of moderate-to-severe primary restless legs syndrome (RLS) in adults.
Gabapentin is the first medication in its class to be approved for the treatment of moderate-to-severe primary RLS, a statement from the companies notes. The drug's efficacy in the treatment of moderate-to-severe primary RLS was confirmed in two 12-week clinical trials in adults.
"Our experience has shown that patients with moderate-to-severe primary RLS can suffer from a range of disruptive symptoms and may benefit from a new treatment option," said Richard K. Bogan, MD, chairman and chief medical officer of SleepMed of South Carolina in Columbia, a clinical trial investigator, in the company release.
Gabapentin enacarbil extended-release tablets are absorbed via the body's nutrient transport mechanisms. The drug is then converted into gabapentin, which binds to a specific type of calcium channel receptor, with no known affinity for other receptors. However, the exact mechanism of action of this agent in treating RLS is unknown.
Gabapentin enacarbil extended-release tablets are not interchangeable with other forms of gabapentin because of differing pharmacokinetics. The same doses of this and other gabapentin products result in different plasma concentrations of gabapentin.
The newly approved drug may cause significant driving impairment, the statement notes. In three 12-week clinical trials, the 2 most commonly observed adverse reactions for the 600 mg per day (n = 163) and 1200 mg per day (n = 269) doses were lethargy (20%, 27%) and dizziness (13%, 22%), compared with 6% and 4%, respectively, with placebo (n = 245).
The recommended dosage is 600 mg once daily taken with food at about 5:00 pm. In addition, the new formulation is contraindicated for patients who need to sleep during the day and remain awake at night.
Gabapentin is an antiepileptic drug. This class of drugs has been associated with an increased risk for suicidal thoughts, depression, and mood changes.
The prevalence for RLS in adults with medically significant symptoms ranges from 1.5% to 2.7% in the United States and/or Western Europe. Diagnostic criteria for RLS include an urge to move the legs usually accompanied or caused by uncomfortable leg sensations, symptoms begin or worsen during periods of inactivity and are partially or totally relieved by movement at least as long as the activity continues, and symptoms are worse or occur only in the evening or night. Potential genetic variants of RLS may exist.
Full prescribing information is available on the GlaxoSmithKline Web site.
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