μ-opioid receptor genetic polymorphisms and duration of epidural fentanyl analgesia during early labor

Epidural fentanyl is commonly used for initiation of early labor analgesia. The aim of this prospective study is to test the hypothesis that duration of epidural fentanyl analgesia differs in nulliparous women requesting epidural analgesia in early labor who are variant allele carriers of the OPRM1 SNVs 118A>G rs1799971, IVS2+31G>A rs9479757, and IVS2+691G>C rs2075572.

Two hundred and twenty parturients who received epidural analgesia with fentanyl were included in the 118A>G analysis, and a 196 sub-cohort was included in the IVS2+31G>A and IVS2+691G>C exploratory analysis. Peripheral blood DNA was genotyped using Taqman allele discrimination assays.

One hundred and seventy-four subjects (79%; 95% CI: 74-84) were homozygous for the wild type OPRM1 118A>G SNV (AA), and forty-six subjects (21%; 95% CI: 16-26) were heterozygous AG (N.=40) or homozygous GG (N.=6) for the variant allele. The minor allele frequency (MAF) was hence 12%. The MAFs for the IVS2+31G>A and IVS2+691G>C SNVs in the sub-cohort of 196 participants were 5% and 59% respectively. There was no significant difference in duration of epidural fentanyl analgesia for the three SNVs (161±68 and 143±51 min for wild type and allele carriers of the 118A>G SNV respectively [P=0.08]). Similarly, no significant differences were shown with the visual analog scale scores, side effects, and satisfaction for each of the three SNVs.

OPRM1 SNVs did not affect the duration of epidural fentanyl administered for early labor analgesia in nulliparous women. These results should be confirmed in patients receiving epidural opioids in other clinical settings.