The quality of evidence is downgraded by study limitations (unclear blinding), and by imprecise results (few patients and outcome events).
A Cochrane review [Abstract] 1 included 5 studies with a total of 687 subjects. Four studies (n=637) included patients with painful diabetic neuropathy and 1 study (n=50) patients with postherpetic neuralgia. All studies used a placebo comparator, although one study used an active placebo (benztropine). Modified-release oxycodone (oxycodone MR) was titrated to effect and tolerability. One study used a fixed dose combination of oxycodone MR and naloxone. Two studies added oxycodone therapy to ongoing, stable treatment with either pregabalin or gabapentin.
Three studies in painful diabetic neuropathy reported outcomes equivalent to 'moderate benefit' (at least 30% pain relief or who were much or very much improved), which was experienced by 44% of participants with oxycodone and 27% with placebo (RR 1.7, 95% CI 1.3 to 2.1; 3 studies, n=587; NNB 5.7).One study on patients with postherpetic neuralgia reported that 58% of participants treated with oxycodone MR and 18% treated with placebo experienced at least moderate pain relief (at least 3 on a scale of 0 to 5). Group mean data showed a statistically significant improvement in pain relief, steady pain, allodynia, and paroxysmal spontaneous pain with oxycodone MR, and global effectiveness and disability were better with oxycodone MR.
All studies reported group mean pain scores at the end of treatment. Three studies reported a greater pain intensity reduction and better patient satisfaction with oxycodone MR alone than with placebo. There was a similar result in the study adding oxycodone MR to stable, ongoing gabapentin, but adding oxycodone MR plus naloxone to stable, ongoing pregabalin did not show any additional effect.
More participants experienced adverse events with oxycodone MR alone than with placebo (86% vs. 63%, RR 1.4, 95% CI 1.2 to 1.5, statistical heterogeneity I2 =65%; 3 studies, n=349; NNH 4.3). Serious adverse events (oxycodone 3.4%, placebo 7.0%) and adverse event withdrawals (oxycodone 11%, placebo 6.4%) were not significantly different between groups. Withdrawals due to lack of efficacy were less frequent with oxycodone MR than placebo (1.1% vs. 11%, RR 0.12, 95% CI 0.03 to 0.45; 3 studies, n=349, number needed to treat to prevent one withdrawal = 10). The add-on studies reported similar results, except for adverse event withdrawals which were more common in add-on oxycodone compared to placebo (14% vs. 4.2%, RR 3.26, 95% CI 1.62 to 6.56; 2 studies, n=426; NNH 10).Constipation, nausea, dizziness, and somnolence, which are typical opioid adverse events, were all more frequent with oxycodone MR than with placebo.
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