ABCB1 encodes MRP1, a transporter that regulates absorption of and central nervous system exposure to drugs. The rs1045642 variant has been associated with a reduced expression of MRP1 mRNA levels and/or a reduction in protein expression in some tissues (Hoffmeyer et al., 2000; Wang et al., 2005). Lower levels of MRP1 may increase access of opioids to the CNS.
Negative results: Despite several positive association studies, a 2015 literature review and meta-analysis found no evidence for association of rs1045642 with opioid use for acute postoperative pain (Ren et al., 2015). In another review (Somogyi et al., 2015), the authors conclude there are no consistent findings for ABCB1 in the pharmacogenetics of opioid response. In addition, a large study of 2,294 cancer patients found no association of any of eight ABCB1 SNPs (rs4437575, rs2235013, rs2235033, rs1128503, rs1202170, rs7802773, rs13229143, and rs1045642) with opioid dose for cancer pain (Klepstad et al., 2011).
Other negative results: