Effects of the OPRM1 A118G Polymorphism (rs1799971) on Opioid Analgesia in Cancer Pain: A Systematic Review and Meta-Analysis

Objectives: Although previous studies have demonstrated that the OPRM1 A118G polymorphism may influence the analgesia response to cancer pain, the results are inconsistent. In this article we aimed to fully examine the association between OPRM1 A118G (rs1799971) polymorphism and opioid analgesia by analyzing published information. This will provide information for better cancer pain management.

Materials And Methods: A systematic search of the literature dating to August 31, 2017 was conducted using PubMed, EMBase, Sinomed, and the Cochrane Library databases. The standardized mean difference (SMD) of required amounts of opioids between AA homozygotes and the G-allele was calculated. Subgroup analyses for race and opioid use was performed. In addition, drug sensitivity analysis, heterogeneity description, and publication bias assessment were performed.

Results: Of the 467 screened studies, 12 including 2118 participants were eligible to be included in our analysis. The meta-analysis results indicated that G-allele carriers (AG+GG) of the OPRM1 A118G polymorphism required higher opioid doses for pain management than those with the AA homozygotes (SMD=-0.3; 95% confidence interval [CI], -0.45 to -0.15; P<0.001). In subgroup analysis, we did not find statistically significant correlation between OPRM1 A118G polymorphism and opioid pain relief among Caucasian patients (SMD=-0.15; 95% CI, -0.29 to -0.00; P=0.04), as well as among morphine users (SMD =-0.20; 95% CI, -0.40 to 0.00, P=0.05), except for Asian patients (SMD=-0.42; 95% CI, -0.62 to -0.23; P<0.001).

Discussion: Our meta-analysis indicates that G allele (AG+GG) carriers of OPRM1 A118G polymorphism required more opioid analgesia in cancer pain management. The OPRM1 A118G polymorphism may help predict individuals' response to analgesia and achieve satisfactory cancer pain control.