Association Of OPRM1 And CYP3A Gene Polymorphisms With Fentanyl Analgesic Effect

Background and ObjectiveFentanyl is a synthetic opioid widely used for analgesia.The analgesia effect of fentanyl varies in different individuals,which makes it difficult to know the appropriate dose for a particular patient.Recent advances in genetic research indicated that genetic polymorphisms may also contribute to the patient's variability in response to opioid treatment.This study was performed to observe the impact ofμ-opioid receptor gene A118G,CYP3A4~*1G and CYP3A5~*3 polymorphisms on fentanyl effect for intravenous analgesia.The present study provides an important foundation and theoretical evidence for the gene-directed rationalization and individualization of medication in the pain treatment.Materials and Methods1.SubjectsTotal two hundred and four subjects,aged 20-50 yr,within±20%of ideal body weight,and having an American Society of Anesthesiologists(ASA) physical status ofⅠorⅡ,undergoing selective abdominal total hysterectomy or myomectomy with general anesthesia were included.Exclusion criteria included the following:known history of psychiatric disease,significant cardiovascular disease,hepatic or renal dysfunction,diabetes mellitus,alcohol or drug abuse,chronic analgesic use, pregnancy or nursing.Subjects who have consumed drugs known to inhibit or induce the expression of CYP3A enzymes in two weeks were also excluded.The study design was approved by Institutional Ethics Committee of Zhengzhou University.The subjects were divided into three groups according to the genotypes.2.Anesthetic Technique and AnalgesiaPreoperatively,the pain threshold and pain tolerance threshold were measured using electrical stimulation.To familiarize the subjects with the assessment method,a training session was given in the preoperative holding area.The pain threshold(PT) and pain tolerance threshold(PTT) for each patient was obtained by the mean of three successive measurements,with a time interval of 5 min.A standardized,general anesthesia technique was used for all subjects.General anesthesia was induced with 0.1mg/kg midazolam,0.5 mg/kg propofol,2μg/kg remifentanyl and 1 mg/kg succinylcholine.Atracurium 0.6 mg/kg was administered intravenously as an initial dosage immediately after tracheal intubation was confirmed and then 0.1-0.2 mg/kg was administered as repeated boluses.During the operation,remifentanyl(0.1-0.2μg/kg/min) and propofol(6-8 mg/kg/h) were used for maintenance of anesthesia. Intravenous fentanyl patient-controlled analgesia(PCA) was provided postoperatively for satisfactory analgesia.The degrees of pain during PCA treatment were assessed with visual analog scale(VAS).The fentanyl consumption and occurrence of any adverse effects in the first 24 h postoperatively were recorded.The analgesic solution in the PCA pump(6300 CADD-Legacy,USA) contained 100 ml normal saline and 1 mg fentanyl,5 mg droperidol.The PCA pump was programmed to give a 2ml bolus of fentanyl solution with 5 min lockout time,0.5 ml/h background infusion and maximum 145μg per hour.3.Genotyping assaysVenous blood samples(2 ml) were collected from all subjects in this study.DNA was extracted from leukocytes using a standard phenol/chloroform procedure. Genotyping of OPRM1 A118G and CYP3A4~*1G,CYP3A5~*3alleles was conducted by polymerase chain reaction-restriction fragment length polymorphism(PCR-RFLP).4.Evaluation of CYP3A activityCYP3A activity was measured by plasma 1'-hydroxymidazolam:midazolam (1'-OHMDZ:MDZ) ratio at 60 min after intravenous administration of 0.1 mg/kg midazolam for induction of anesthesia.Midazolam and 1'-hydroxymidazolam concentrations were determined using liquid chromatography-mass spectrometry method(LC-MS).5.Statistical analysisSPSS 13.0 software was used for statistical analyses.The allele frequencies were estimated from the observed numbers of each specific allele.Chi-square test was used to verify Hardy-Weinberg equilibrium.One-way analysis of variance was used to assess whether significant differences exist between the three genotypes.Data for the fentanyl consumption were compared among the genotype group using one-way analysis of variance with post hoc Bonferroni correction for multiple comparisons was performed before and after adjusted for age,weight and remifentanil consumption in the operation.The incidences of any adverse effects were analyzed using Chi-square test or Fisher exact test.Theαwas set at 0.05.Results1.General informationAmong the 204 subjects,the preoperative pain threshold was 2.0±0.6 mA,and the pain tolerance threshold was 5.1±2.0 mA.The VAS pain score immediately after surgery was 5.7±1.4.At 24 h after surgery,it was 2.2±0.8.The fentanyl consumption was 396.2±210.0μg and 190.9±43.2μg in the postoperative first and second 24 h, respectively.The incidence of PONV within 24 h in our study was 28.92%.2.Frequencies of OPRM1 A118G,CYP3A4~*1G and CYP3A5~*3 allelesThe frequencies of OPRM1 118G,CYP3A4~*1G and CYP3A5~*3 alleles in Chinese gynecologic patients were 0.320,0.299 and 0.694,respectively.The allele frequencies were in Hardy-Weinberg equilibrium(P＞0.05).3.Association of OPRM1 A118G gene polymorphism with preoperative pain tolerance and fentanyl analgesic effectThere were no significant differences in general information among the three genotype groups(P＞0.05).PTT was statistical different between A/A(5.6±2.4 mA) and A/G(4.9±1.3 mA) groups,between A/G and G/G(3.8±1.0 mA) groups and between A/A and A/G groups(P＜0.05).However,PT did not show a significant difference among the three genotypes(P＞0.05).Subjects in G/G group(507.9±290.2μg) consumed significantly more fentanyl than subjects in A/A(363.6±198.8μg) and A/G(412.0±189.8μg) groups in the first 24 h postoperatively(P＜0.05).Fentanyl consumption increased in accordance with the number of OPRM1 118G alleles (P＜0.05 for linear trend).There was no significant difference in incidences of adverse events among the different genotype groups(P＞0.05).4.Association of CYP3A4~*1G gene polymorphism with CYP3A activity and fentanyl analgesic effectThere were no significant differences in general information among the three genotype groups(P＞0.05).The subjects with the CYP3A4~*1G/~*1G genotype (260.0±101.1μg) need less fentanyl to achieve pain control than subjects carrying the CYP3A4~*1/~*1(407.4±187.4μg) and CYP3A4~*1/~*1G(414.1±238.5μg) genotypes (P＜0.05).Fentanyl consumption increased in accordance with the number of ~*1G alleles(P＜0.05 for linear trend).The activity of CYP3A in ~*1G/~*1G group(0.34±0.15) was lower than in ~*1/~*1(0.46±0.14) and ~*1/~*1G(0.46±0.12) groups(P＜0.05).There was no significant difference in incidences of adverse events among the different genotype groups(P＞0.05).5.Association of CYP3A5~*3 gene polymorphism with CYP3A activity and fentanyl analgesic effectThere were no significant differences in general information among the three genotype groups(P＞0.05).There were no significant differences in postoperative fentanyl consumptions or in CYP3A activity among the three genotype groups (P＞0.05).There was no significant difference in incidences of adverse events among the different genotype groups(P＞0.05).6.Effect of CYP3A4/CYP3A5 haplotype on fentanyl analgesic effectFor CYP3A4/CYP3A5 haplotype,the subjects possessing CYP3A4~*1G/CYP3A5~*3 haplotype(CYP3A4~*1G/~*1G and CYP3A5~*1/~*3 or CYP3A5~*1/~*3) need less fentanyl to achieve pain control than subjects possessing CYP3A4~*1/CYP3A5~*1 haplotype(CYP3A4~*1/~*1 and CYP3A5~*1/~*1)(P＜0.05).7.Joint effects of OPRM1 A118G and CYP3A4~*1G gene polymorphisms on fentanyl analgesic effectTo explore the joint effects of genes and the clinical efficacy of fentanyl,we created four groups:(1) ~*1G/~*1G but not G/G;(2) neither G/G nor ~*1G/~*1G;(3) G/G and ~*1G/~*1G;(4) G/G but not ~*1G/~*1G.There was significant difference in fentanyl consumption among the four genotype groups.Carriers of the OPRM1 118G/G and the CYP3A4~*1 genotypes required the most fentanyl dose(P＜0.05).There was no significant difference in incidence of adverse events among the different genotype groups(P＞0.05).Conclusions1.The preoperative pain tolerance threshold is lower in OPRM1 118G homozygotes. The OPRM1 A118G polymorphism has a gene-dose-dependent effect on the pain tolerance threshold.Postoperative fentanyl consumption increase in accordance with the number of 118G alleles.This is the first report on the association of OPRM1 A118G polymorphism with the effect of fentanyl for intravenous analgesia.2.Carrying CYP3A4~*1G decrease the activity of CYP3A4 and patient-controlled intravenous fentanyl consumption.CYP3A5~*3 polymorphism may have no significant impact on fentanyl analgesic effect.For CYP3A4/CYP3A5 haplotype, CYP3A4~*1G/CYP3A5~*3 decrease the consumption of fentanyl for intravenous analgesia.This is the first report on the association of CYP3A4~*1G polymorphism with the effect of fentanyl.3.Carriers of the OPRM1 118G/G and the CYP3A4~*1 genotypes require the most fentanyl dose when explored for joint effects of OPRM1 and CYP3A4 genes.