Morphine is the analgesic of choice for moderate to severe cancer pain; however, 10-30% of patients do not tolerate morphine. This study evaluated genetic variation in the m-opioid receptor, barrestin2, stat6 and uridine diphosphate-glucuronysltransferase 2B7 (UGT2B7) genes, in patients who responded to morphine vs those who were switched to alternative opioids. We prospectively recruited and genotyped 162 Caucasian patients (117 controls, 39 switchers). Switchers, were more likely to carry the common allele at 1182 G/A, 5864 G/A, 8622T/C and 11143 G/A in the barrestin2 gene (P ¼ 0.021, 0.043, 0.013, 0.043, respectively). Switchers had increased carriage of the T allele (À1714 C/T) and a significant difference in the allelic frequency at 9065 C/T (w 2 ¼ 3.86, P ¼ 0.049) in the stat6 gene. No differences were seen in genotype or allele frequencies of SNPs in the mopioid receptor gene or UGT2B7 gene. This study presents novel data suggesting that variation in genes involved in m-opioid receptor signalling influence clinical response to morphine.

We conclude that gabapentin is an effective treatment for cancer-related neuropathic pain.

This study has shown that proactive clinical identification and management of patients that require opioid switching is reproducible in different clinical settings and significantly improves pain control. Further studies are required to develop and test the predictive model.