Association Of Cyp3a4~*1g Polymorphism With Fentanyl Intravenous Analgesic Effect

Background and ObjectiveFentanyl is a synthetic opioid that has been widely used in clinical practice and it is especially effective for induction and maintenance of anesthesia or control of analgesia.However,the effective dose of fentanyl for pain control varies greatly among individuals.Fentanyl is metabolized in the liver predominantly by the cytochrome P450 3A4(CYP3A4).CYP3A4 protein expression in the liver may vary up to 40-fold,leading to variations in drug metabolism and contributing to differences in individual response to the drug.Genetic variation within the CYP3A4 gene may contribute to interindividual variability in drug metabolism.Single nucleotide polymorphisms(SNPs) are the most common form of genetic variation in the CYP3A4.CYP3A4~*1G is a high-frequency allele in Chinese,the alteration of function remains unclear in vitro and in vivo.The influence of CYP3A4~*1G on fentanyl analgesic effect has not been reported.Due to the importance of CYP3A4 in the metabolism of fentanyl,we conducted this study to observe the impact of CYP3A4~*1G polymorphism on fentanyl effect for intravenous analgesia.The present study provides an important foundation and theoretical evidence for individualization of medication in the pain treatment.Materials and Methods1.SubjectsTotal one hundred and ninety patients,having an American Society of Anesthesiologists(ASA) physical status ofⅠorⅡ,aged 20-50 yr,within±20%of ideal body weight,who were admitted into our medical institution for elective abdominal total hysterectomy or myomectomy,were enrolled in the current study. Patients with a known history of significant cardiovascular disease,diabetes mellitus, alcohol or drug abuse,hepatic or renal dysfunction,pregnancy or nursing,and chronic analgesic use were excluded from the study.Patients who had consumed drugs known to inhibit or induce the expression of CYP3A4 enzymes one month prior to surgery were also excluded.The patients were divided into three groups according to the genotypes.2.Anesthetic Technique and AnalgesiaAll patients gave written informed consent for participating in the study and the study protocol was approved by the Institution Review Board at Zhengzhou University.A standardized general anesthesia protocol was used for all patients.We administered 0.1mg/kg midazolam,0.5 mg/kg propofol,2μg/kg remifentanil and 1 mg/kg succinylcholine for induction of anesthesia.Atracurium 0.6 mg/kg was administered intravenously as an initial dosage immediately after tracheal intubation was confirmed and then 0.1 to 0.2 mg/kg was administered by repeated boluses and 0.1 to 0.2μg/kg/min remifentanil and 6 to 8 mg/kg/h propofol were infused for maintenance of anesthesia.Postoperative PCA(1 mg fentanyl and 5 mg droperidol in 100 ml normal saline) was administered using a computer controlled infusion pump (CADD-Legacy 6300) which was programmed to give a 2 ml bolus of fentanyl solution with a 5 min lockout time,0.5 ml/h background infusion and a maximum of 145μg per hour.All patients received intravenous PCA with fentanyl once they were stable and awake.The delivered dose of fentanyl was recorded.VAS was used for assessing pain at rest during PCA.Successful analgesia was defined as a VAS score≤3.The VAS score and incidence of any adverse effects such as nausea,vomiting, respiratory depression and sedation were recorded.3.Genotyping assaysVenous blood samples were collected from all patients.DNA was extracted using a standard phenol/chloroform procedure.Genotyping of CYP3A4~*1G allele was conducted by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).The results for each genotype were confirmed in randomly selected individuals by direct sequence analysis.4.Evaluation of CYP3A4 activityPeripheral blood sample(5 ml) was collected from each patient.CYP3A4 activity was measured by determining the plasma ratio of 1'-hydroxymidazolam to midazolam 1 h after intravenous administration of 0.1 mg/kg midazolam for induction of anesthesia.Midazolam and 1'-hydroxymidazolam concentrations were determined using a liquid chromatography-mass spectrometry.5.Statistical analysisSPSS 11.0 software was used for statistical analyses.Values were reported as (?)+s.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 using one-way analysis of variance with post hoc Bonferroni correction,multiple comparisons was performed before and after adjusted for age,weight of the patients and remifentanil consumption in the operation.The incidences of any adverse effects were analyzed using Chi-square test or Fisher exact test.A two tailed P-value of＜0.05 was considered statistically significant.Results1.General informationAmong the 190 patients,the VAS pain score immediately postoperatively was 5.7±1.4.At 24 h after surgery,it was 2.2±0.8.No one needed rescue management for inadequate pain control.The fentanyl consumption was 391.5±201.7μg and 191.2±43.5μg in the first and second 24 h postoperatively,respectively.The incidence of postoperative nausea and vomiting was 28.9%.The incidence of mild sedation and pruritus in our study was 1.6%and 0.5%,respectively.2.Frequency of CYP3A4~*1G alleleThe frequency of CYP3A4~*1G allele in gynecologic patients was 29.7%.The allele frequency was in Hardy-Weinberg equilibrium(P＞0.05).The allelic frequency of CYP3A4~*1G in our study was similar to that reported in Japanese(24.9%) and Chinese hyperlipidemic patients(27.6%)(P＞0.05).3.Association of CYP3A4~*1G gene polymorphism with CYP3A4 activity and fentanyl analgesic effectThere were no significant differences in general information among the three genotype groups(P＞0.05).No statistical difference in postoperative VAS pain scores was detected across genotypes.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(406.7±186.6μg) and CYP3A4~*1/~*1G(396.8±222.6μg) genotypes (P＜0.05).Fentanyl consumption increased in accordance with the number of ~*1G alleles(r=-0.14,P＜0.05 for linear trend).The activity of CYP3A4 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).Conclusions1.The frequency of CYP3A4~*1G allele in Chinese gynecologic patients is 29.7%.2.Carrying CYP3A4~*1G decrease the activity of CYP3A4 and patient-controlled intravenous fentanyl consumption.