Analgesic Effects of Gabapentin Assessed in Chronic Neuropathic Pain
Gabapentin, at doses of 1800mg to 3600mg (1200mg to 3600mg gabapentin encarbil) can provide “good levels of pain relief” to some individuals suffering from postherpetic neuralgia and peripheral diabetic neuropathy, according to a Cochrane Database Systematic Review.
Wiffen et al. analyzed 37 studies (n=5914) which included participants who had some form of neuropathic pain, predominantly postherpetic neuralgia and painful diabetic neuropathy. Most studies used oral gabapentin or gabapentin encarbil at doses of ≥1200mg daily, and study duration was typically 4 to 12 weeks.
Primary outcomes were participants with “substantial” pain relief (≥50% pain relief over baseline, or “very much improved” on Patient Global Impression of Change Scale [PGIC]), or moderate pain relief (≥30% pain relief over baseline or much/very much improved on PGIC). The researchers performed a pooled analysis for any substantial or moderate benefit.
In postherpetic neuralgia, more participants had substantial benefit with gabapentin at ≥1200mg daily than with placebo (32% vs 17% respectively; RR 1.8 [95% CI 1.5 to 2.1]; NNT 6.7 [5.4 to 8.7]). More participants (46%) had moderate benefit with gabapentin at ≥1200mg daily than with placebo (46% vs 25%; RR 1.8 [95% CI 1.6 to 2.0]; NNT 4.8 [4.1 to 6.0]).
In painful diabetic neuropathy, more participants had substantial benefit with gabapentin at ≥1200mg daily than with placebo (38% vs 21% respectively; RR 1.9 [95% CI 1.5 to 2.3]; NNT 5.9 [4.6 to 8.3]). More participants had moderate benefit with gabapentin at 1200mg daily or greater than with placebo (52% vs 37% respectively; RR 1.4 [95% CI 1.3 to 1.6]; NNT 6.6 [4.9 to 9.9]).
For all conditions combined, adverse event withdrawals were more common with gabapentin compared to placebo (11% vs 8.2% respectively; RR 1.4 [95% CI 1.1 to 1.7]; NNH 30 [20 to 65]). Adverse events included dizziness (19%), somnolence (14%), peripheral edema (7%), and gait disturbance (14%).
The researchers noted that the outcome of ≥50% reduction in pain intensity is “regarded as a useful outcome of treatment by patients, and the achievement of this degree of pain relief is associated with important beneficial effects on sleep interference, fatigue, and depression, as well as quality of life, function, and work.”
Their findings demonstrated that 3 or 4 out of 10 participants achieved this degree of pain relief with gabapentin, vs. 1 or 2 out of 10 for placebo; however, they added, “over half of those treated with gabapentin will not have worthwhile pain relief but may experience adverse events.”
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