Rescue and concomitant analgesics in placebo-controlled trials of pharmacotherapy for neuropathic pain and low back pain.

Rescue medication is commonly offered to participants in placebo-controlled trials of analgesic drugs. The use of pain medication in addition to the placebo or experimental drug may complicate the interpretation of effects and tolerability, but this issue has received little methodological attention. This study examined the handling and reporting of rescue and concomitant analgesic use in trials of pharmacotherapy for neuropathic pain and low back pain. We based our review on 265 trials included in two recent systematic reviews, 83 trials of low back pain and 182 of neuropathic pain. In total, 117 (44%) trials permitted rescue medication and 126 (48%) allowed participants to continue all or some of their usual analgesics. The utilization of rescue medication increased over time, occurring in 18% of trials before 2000 compared with 55% after 2000. Forty-one trials (16%) permitted both rescue analgesics and continued use of prestudy analgesics. More than one-third of the trials permitting rescue medication did not report the actual rescue drug consumption, and over half of the trials allowing concomitant analgesics did not report whether intake changed during the trial. Only 22 (19%) of the trials permitting rescue medication included complete information about whether rescue medication was used as an outcome, specified the drugs used, specified how consumption was assessed and measured, and reported and analyzed the use of rescue medication in each trial arm. Our findings suggest that poorly described procedures and incomplete reporting are likely to hinder the interpretation, critical appraisal, and replication of trial results.