In
neuropathic pain it has been suggested that
pain phenotype based on putative
pain mechanisms may predict response to treatment. This was a randomised, double-blind, placebo-controlled, and phenotype-stratified study with 2 6-week treatment periods of
oxcarbazepine (1800-2400mg) and placebo. The primary efficacy measure was change in median
pain intensity between baseline and the last week of treatment measured on an 11-point numeric rating scale, and the primary objective was to compare the effect of
oxcarbazepine in patients with and without the irritable nociceptor phenotype as defined by
hypersensitivity and preserved small nerve fibre function determined by detailed quantitative sensory testing. Ninety-seven patients with peripheral
neuropathic pain due to
polyneuropathy, surgical or traumatic nerve injury, or
postherpetic neuralgia were randomised. The intention-to-treat population comprised 83 patients: 31 with the irritable and 52 with the nonirritable nociceptor phenotype. In the total sample,
oxcarbazepine relieved
pain of 0.7 points (on a numeric rating scale 0-10; 95% confidence interval [CI] 0.4-1.4) more than placebo (P=0.015) and there was a significant interaction between treatment and phenotype of 0.7 (95% CI 0.01-1.4, P=0.047). The number needed to treat to obtain one patient with more than 50%
pain relief was 6.9 (95% CI 4.2-22) in the total sample, 3.9 (95% CI 2.3-12) in the irritable, and 13 (95% CI 5.3-∞) in the nonirritable nociceptor phenotype. In conclusion,
oxcarbazepine is more efficacious for relief of peripheral
neuropathic pain in patients with the irritable vs the nonirritable nociceptor phenotype.