Background: Morphine consumption after a given surgical procedure can vary considerably. Studies show that single nucleotide polymorphism involving the nucleotide position 118 at exon 1 of the m-opioid receptor gene (OPRM1) may play a role in mediating the effects of opioids. This study was performed to correlate the A118G polymorphism at OPRM1 with morphine consumption in patients undergoing total knee arthroplasty. Methods: Post-operative pain was relieved by patient-controlled analgesia (PCA). The analgesic effect was evaluated using a visual analogue scale. Side-effects, such as sedation, nausea and vomiting, and pruritus, were recorded systematically. The genotypes were determined by sequencing polymerase chain reactionamplified DNA. The differences in demographics and consumed morphine from the PCA device between the different genotypes were tested using one-way analysis of variance. The prevalence of side-effects from morphine and sex distribution were compared using the Kruskal-Wallis test. Results: One hundred and forty-seven patients were included in the study. Twenty-seven patients who required rescue analgesia were excluded; these patients did not differ demographically or

SummaryOne hundred and seventy-four Chinese gynaecology patients were studied for the impact of A118G polymorphism in the l-opioid receptor gene (OPRM1) on pain sensitivity and postoperative fentanyl consumption. Pre-operatively, the pain threshold and pain tolerance threshold were measured using electrical stimulation. A118G polymorphism was genotyped using the polymerase chain reaction-restriction fragment length polymorphism method. Intravenous fentanyl patient-controlled analgesia provided postoperative pain management, assessed using a visual analogue scale and fentanyl consumed in the first 24 h after surgery was noted. We found the prevalence of G118 allele was 31.3%. The A118G polymorphism had a gene-dose-dependent effect on electrical pain tolerance threshold. Fentanyl consumption was also significantly different in patients with different OPRM1 genotypes (homozygotes for 118G consumed more than did heterozygotes or homozygotes for 118A). Fentanyl consumption increased in accordance with the number of 118G alleles. We conclude that OPRM1 gene analysis may help predict individual opioid sensitivity and so optimise postoperative pain control.

No abstract