A118G single nucleotide polymorphism of human mu-opioid receptor gene influences pain perception and patient-controlled intravenous morphine consumption after intrathecal morphine for postcesarean analgesia.
BACKGROUND
Previous studies have shown that genetic variability at position 118 of the human mu-opioid receptor gene altered patients' response to intravenous morphine. The purpose of this study was to investigate whether this polymorphism contributes to the variability in response to morphine for postcesarean analgesia.


METHODS
After investigators obtained informed consent, 588 healthy women received 0.1 mg intrathecal morphine for postcesarean analgesia. Their blood samples were genotyped for the A118G polymorphism-A118 homozygous (AA), heterozygous (AG), or homozygous for the G allele (GG). Pain scores, the severity of nausea and vomiting, the incidence of pruritus, and the total self-administered intravenous morphine were recorded for the first 24 postoperative hours.


RESULTS
Two hundred seventy women (46%) were AA, 234 (40%) were AG, and 82 (14%) were GG. The 24-h self-administered intravenous morphine consumption was lowest in the AA group (P = 0.001; mean, 5.9; 95% confidence interval, 5.1-6.8) versus the AG (8.0; 6.9-9.1) and GG groups (9.4; 7.3-11.5). Pain scores were lowest in the AA group and highest in the GG group, with a statistically significant difference detected between AA, AG, and GG (P = 0.049). Total morphine consumption was also influenced by patients' age and paying status. AA group was associated with the highest incidence of nausea (26 of 272 [9.6%]; P = 0.02) versus the other two groups (13 of 234 [5.6%] and 1 of 82 [1.2%] for AG and GG, respectively).


CONCLUSIONS
Genetic variation at position 118 of the mu-opioid receptor is associated with interindividual differences in pain scores, self-administered intravenous morphine, and the incidence of nausea postoperatively.
Sia
Alex T
AT
Department of Women's Anaesthesia, KK Women's and Children's Hospital, 100 Bukit Timah Road, Singapore. alex.sia.th@kkh.com.sg
Lim
Yvonne
Y
Lim
Eileen C P
EC
Goh
Rachelle W C
RW
Law
Hai Yang
HY
Landau
Ruth
R
Teo
Yik-Ying
YY
Tan
Ene Choo
EC
D000328:Adult; D000367:Age Factors; D016362:Analgesia, Obstetrical; D016058:Analgesia, Patient-Controlled / Q000379:methods / Q000706:statistics & numerical data*; D000701:Analgesics, Opioid / Q000008:administration & dosage*; D002585:Cesarean Section / Q000009:adverse effects; D005260:Female; D006801:Humans; D007278:Injections, Spinal; D009020:Morphine / Q000008:administration & dosage*; D010147:Pain Measurement; D010149:Postoperative Pain / Q000188:drug therapy / Q000235:genetics*; D010465:Perception / Q000187:drug effects; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D020250:Postoperative Nausea and Vomiting / Q000235:genetics; D011247:Pregnancy; D011537:Pruritus / Q000235:genetics; D017450:Receptors, Opioid, mu / Q000235:genetics*; D012720:Severity of Illness Index
D000701:Analgesics, Opioid; D017450:Receptors, Opioid, mu; D009020:Morphine