We experience individual differences in
pain and sensitivity to
analgesics clinically. Genetic factors are known to influence individual difference. Polymorphisms in the human OPRM1 gene, which encodes the μ-
opioid receptors, may be associated with the clinical effects of
opioid analgesics. The purpose of this study was to determine whether any of the 5 common single-nucleotide polymorphisms (SNPs) of the OPRM1 gene could affect the antinociceptive effect of
fentanyl.
Fentanyl was less effective in subjects with the G allele of the OPRM1 A118G SNP than in those with the A allele, and subjects with the G allele required more
fentanyl for adequate
postoperative pain control than those with the A allele. In the future, identifying SNPs might give us information to modulate the
analgesic dosage of
opioid individually for better
pain control. Factors underlying individual differences in sensitivity to
pain other than genetic factors may include environmental and psychological factors. We therefore examined the effects of preoperative anxiety on the
analgesic efficacy of
fentanyl in patients undergoing sagittal split
mandibular osteotomy (SSMO). From among the patients enrolled in the study, 60 patients (male/female: 18/42, age: 24.6 ± 6.7 years) who gave informed consent were examined for correlations between preoperative trait/state anxiety, as measured by the state-trait anxiety inventory (STAI) on the day before surgery, and postoperative consumption of
patient-controlled analgesia (PCA)
fentanyl and visual analog scale (VAS) assessment by patients. Levels of trait and state anxieties measured by the STAI were correlated with neither the consumption of PCA
fentanyl nor postoperative VAS assessment. These findings suggest that psychological factors are unlikely to affect
postoperative pain or the use of
analgesics.