Forty-two studies met the inclusion criteria; 12 RCTs reported data on chronic severe pain and 42 RCTs reported data on chronic moderate-to-severe pain.
Severe chronic pain: Overall, the methodological quality of these trials was considered to be good.
Compared to oxycodone, tapentadol was found to significantly reduce pain intensity (MD -2.64, 95% CI -4.84 to -0.44; four RCTs). A significant difference in pain relief of 30% and 50% at the end of treatment in favour of tapentadol was also found. No significant between group difference was found for the incidence of serious adverse events (four RCTs), but tapentadol was found to significantly reduce the risk of constipation, nausea, and vomiting (seven RCTs).
Compared to placebo, tapentadol was found to significantly reduce pain intensity (MD -6.33, 95% CI -8.55 to -4.11; five RCTs). A significant difference in favour of tapentadol in pain relief of 30% and 50% was also found. No significant between group difference was found for the incidence of serious adverse events (three RCTs), but tapentadol was found to significantly increase the risk of constipation, nausea, vomiting, somnolence, and dizziness (six RCTs).
Moderate-to-severe chronic pain: Overall, the methodological quality of these trials was considered to be poor, although the tapentadol trials were of good quality.
Compared with oxycodone, a significant difference in favour of tapentadol was found for pain intensity (MD -2.45, 95% CI -4.04 to -0.86; seven RCTs), and incidence of serious adverse events (RR 0.53, 95% CI 0.28 to 1.00). A significant difference was also found for, pain relief 30% and 50%.Tapentadol was also found to increase quality of life (five RCTs) and reduce the incidence of constipation, nausea, and vomiting (seven RCTs).
Compared with placebo, tapentadol reduced pain intensity (MD -6.91, 95% CI -9.80 to -4.02; six RCTs). A significant difference in favour of tapentadol in pain relief 30% and 50% was also found. No significant between group difference was found for the incidence of serious adverse events (six RCTs). Tapentadol was found to improve quality of sleep (four RCTs), quality of life (five RCTs), and scores on the Patients' Global Impression of Change scale (six RCTs), but increase the incidence of constipation, nausea, vomiting, somnolence, dizziness, and discontinuation rates for all causes and serious adverse events (six RCTs).
Indirect comparisons were also reported (see paper for more complete details); in general these results supported the head-to-head trials.