Pharmacotherapeutic Options for Managing Neuropathic Pain: A Systematic Review and Meta-Analysis

Table 4

Randomized, double-blind, controlled trials testing the effect of opioids.

Study	Active drug	Control	Sample size	NP condition	Outcome measure	Pain outcome	Adverse events
Gavin et al. [24]	Oxycodone patch 23.6 mg/72 hours	Placebo	28	PHN	0–10 NRS	Negative	Application site irritation (18.5%), infections (7.4%), respiratory disorders (7.4%), gastrointestinal disorders (3.7%), musculoskeletal, and connective tissue disorders (3.7%)
Rigo et al. [25]	Methadone 3 mg; ketamine 30 mg	Methadone 3 mg or ketamine 30 mg	42	Refractory NP	VAS	Negative	Somnolence (46%), nausea (23%), vomiting (15%), and constipation (8%)
Simpson and Wlodarczyk [26]	Buprenorphine patch <40 mg/h	Placebo	93	DPN	0–10 NRS	Negative	Nausea (43.0%) and constipation (31.2%)
Gilron et al. [27]	Morphine 10 mg; nortriptyline 10 mg	Nortriptyline 10 mg or morphine 10 mg	52	Peripheral NP	0–10 NRS	Positive	Dry mouth (57.5%), constipation (42.5%), and somnolence (20%)

NP: neuropathic pain; DPN: diabetic painful neuropathy; PHN: postherpetic neuralgia; NRS: numerical rating scale; VAS: visual analog scale. A significant pain relief was observed in the ketamine alone group compared with both the methadone and methadone/ketamine groups.