Gabapentin (Neurontin) in Postherpetic Neuralgia
Abstract & Commentary
Synopsis: This multicenter, randomized, parallel design, double-blind, placebo-controlled clinical trial demonstrates that gabapentin (up to 3600 mg/d) is effective in decreasing the pain of postherpetic neuralgia.
Source: Rowbotham M, et al. For the Gabapentin Postherpetic Neuralgia Study Group. Gabapentin for the treatment of postherpetic neuralgia. A randomized controlled trial. JAMA 1998;280:1837-1842.
Gabapentin (neurontin, parke-davis) is a recently introduced anticonvulsant drug, with apparent efficacy in neuropathic pain states. Rowbotham and colleagues describe their experience testing gabapentin for postherpetic neuralgia in a multicenter, randomized, parallel design, double-blind, placebo-controlled clinical trial. Subjects were included if they had symptoms of postherpetic neuralgia for at least three months, and the pain intensity at the time of screening was at least moderate (score of 4 of 10 on a Likert [visual analog] scale for pain). Subjects received gabapentin (up to 3600 mg/d) or matching placebo in a titration period lasting four weeks, followed by another four weeks at the maximum tolerated gabapentin (or placebo) dosage. Subjects prescribed chronic narcotic analgesics or tricyclic antidepressants were permitted to continue receiving these agents, at fixed dosage, however, no other analgesic agents were permitted. Other inclusion and exclusion criteria appeared to be appropriate. Subjects were seen for three follow-up visits (weeks 2, 4, and 8), where standard rating scales for pain, mood, functioning, and quality of life were performed.
One hundred thirteen subjects were randomized to gabapentin (89 [78.8%] completed the study) and 116 to placebo (95 [81.9%] completed the study). The average age of the subjects was 73 years. Gabapentin performed significantly better than placebo for the main outcome measure of reduction in pain intensity (6.3 to 4.2 and 6.5 to 6.0 on the Likert scale, respectively). Gabapentin also did significantly better than placebo in improving the secondary outcome measures, such as sleep, as well as multiple items from the mood and quality-of-life rating scales. As could be expected, adverse effects such as drowsiness, dizziness, edema, and ataxia were more common in the gabapentin group when compared to placebo. For unclear reasons, the rate of unspecified "infection" was substantially greater in the gabapentin group (8.0% vs 2.6%). However, there was little difference in the rate of drop-outs from adverse effects between the gabapentin and placebo groups, indicating the mild-to-moderate nature of these adverse effects, even in this elderly study population. Rowbotham et al correctly conclude that gabapentin is effective for reducing the pain and suffering of patients with postherpetic neuralgia.
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