Background: Recent studies examining the moderating effects of polymorphic variation in opioid receptor genes have yielded conflicting results. We examined opioid receptor gene polymorphisms as moderators of the therapeutic effects of the opioid antagonist nalmefene.
Methods: Participants (n = 272) were subjects who consented to the pharmacogenetic analysis of a multi-site, randomized, placebo-controlled trial of targeted nalmefene for the reduction of heavy drinking. We genotyped two single nucleotide polymorphisms (SNPs) in OPRM1 (including A118G, a commonly studied SNP that encodes an Asn40Asp amino acid substitution), two SNPs in OPRD1, and one SNP in OPRK1, which encode the mu-, delta-, and kappa-opioid receptors, respectively. Regression analysis served to examine the moderating effects of these SNPs on medication response.
Results: As previously described by Karhuvaara et al. (2007), nalmefene significantly reduced the number of heavy drinking and very heavy drinking days per week, compared with placebo. There were no main or moderating effects of the genotypes examined on these outcomes.
Conclusions: Our finding that the therapeutic effects of targeted nalmefene were not moderated by polymorphic variation in opioid receptor genes is consistent with two recent reports showing that variation in opioid receptor genes does not moderate the response to naltrexone. However, these findings contrast with those from two other studies, in which the Asn40Asp polymorphism in OPRM1 moderated the naltrexone treatment response. Additional research is needed to clarify the role of variation in opioid receptor genes on the response to opioid antagonist treatment of alcoholism.