medwireNews: The authors of a meta-analysis report mostly weak evidence, short-term follow-up, and evidence of publication bias in studies of pain relief in patients with diabetic peripheral neuropathy.
The evidence gathered from the 106 randomized, controlled trials broadly supported the drugs currently recommended by the US Food and Drugs Administration: duloxetine; tapentadol; and pregabalin.
However, Julie Waldfogel (The Johns Hopkins Hospital, Baltimore, Maryland, USA) and study co-authors caution that there was evidence of significant publication bias for the anticonvulsant pregabalin. Of the 15 studies of this drug included, five were unpublished, with the data appearing only on ClinicalTrials.gov, and all of these unpublished studies were negative. In addition, there were six further registered studies on ClinicalTrials.gov with no data reported.
Furthermore, the effect size for pregabalin was small, whereas the average effect sizes were moderate or large for other effective agents.
The team graded the strength of evidence for pregabalin and for the atypical opioid tapentadol as low, and for the serotonin–noradrenaline reuptake inhibitor (SNRI) duloxetine as moderate, with the SNRI venlafaxine also having moderate strength of evidence. But all other reportedly effective medications, comprising oxcarbazepine, botulinum toxin, and tricyclic antidepressants, had low strength of evidence.
All comparisons were for the medications versus placebo. “We were unable to draw conclusions for any head-to-head drug comparisons due to insufficient evidence,” write the researchers in Neurology.
A further concern was that most studies lasted for less than 3 months, despite patients with diabetic neuropathy in clinical practice requiring long-term pain relief.
“We could not assess long-term clinical outcomes and harms, including continued effectiveness with progression of [diabetic peripheral neuropathy], long-term side effects, or long-term effect on function or diabetic complications,” say Waldfogel and team.
“This is particularly important for atypical opioids, which we found were effective in short-term studies, as new guidelines and position papers now recommend against the use of opioids for chronic pain conditions given lack of evidence for long-term benefit and increasing evidence of serious risks, particularly abuse, misuse, and overdose.”
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