Opioids for neuropathic pain

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Cochrane Database Syst Rev. 2006 Jul 19;3:CD006146.

Opioids for neuropathic pain.

Eisenberg E, McNicol E, Carr D.

BACKGROUND: The use of opioids for neuropathic pain remains

controversial. Studies have been small, have yielded equivocal

results, and have not established the long-term risk-benefit ratio of

this treatment.

OBJECTIVES: To assess the efficacy and safety of opioid agonists for

the treatment of neuropathic pain.

SEARCH STRATEGY: We searched the Cochrane Central Register of

Controlled Trials (2nd Quarter 2005), MEDLINE (1966 to June 2005),

and EMBASE (1980 to 2005 Week 27) for articles in any language, and

reference lists of reviews and retrieved articles.

SELECTION CRITERIA: Trials were included in which opioid agonists

were given to treat central or peripheral neuropathic pain of any

etiology, pain was assessed using validated instruments, and adverse

events were reported. Studies in which drugs other than opioid

agonists were combined with opioids or opioids were administered

epidurally or intrathecally were excluded.

DATA COLLECTION AND ANALYSIS: Data were extracted by two independent

investigators and included demographic variables, diagnoses,

interventions, efficacy, and adverse effects.

MAIN RESULTS: Twenty-three trials met the inclusion criteria and were

classified as short-term (less than 24 hours; n = 14) or intermediate-

term (median = 28 days; range = eight to 70 days; n = 9). The short-

term trials had contradictory results. In contrast all nine

intermediate-term trials demonstrated opioid efficacy for spontaneous

neuropathic pain. Meta-analysis of seven intermediate-term studies

showed mean post-treatment visual analog scale scores of pain

intensity after opioids to be 13 points lower on a scale from zero to

100 than after placebo (95% confidence interval -16 to -9; P <

0.00001). The most common adverse events were nausea (33% opioid

versus 9% control: number needed to treat to harm (NNH) 4.2) and

constipation (33% opioid versus 10% control: NNH 4.2), followed by

drowsiness (29% opioid versus 12% control: NNH 6.2), dizziness (21%

opioid versus 6% control: NNH 7.1), and vomiting (15% opioid versus

3% control: NNH 8.3). Where reported, 23 (11%) of 212 participants

withdrew because of adverse events during opioid therapy versus nine

(4%) of 202 receiving placebo.

AUTHORS' CONCLUSIONS: Short-term studies provide only equivocal

evidence regarding the efficacy of opioids in reducing the intensity

of neuropathic pain, whereas intermediate-term studies demonstrate

significant efficacy of opioids over placebo, which is likely to be

clinically important. Reported adverse events of opioids are common

but not life threatening. Further randomized controlled trials are

needed to establish long-term efficacy, safety (including addiction

potential), and effects on quality of life.