Effect Of PXR~*1B Haplotype Genetic Polymorphism On Postoperative Analgesia With Fentanyl

Background and ObjectiveFentanyl is the most usually used opioid of all clinically post-operative intravenous analgesics. But the effect of fentanyl intravenous analgesia shows significant inter-individual variations. Recent research advance indicated that genetic factors contributed to the variability of pharmacokinetics and pharmacodynamics by changing the expression level and enzyme activity of enzyme, metabolizing opioids. Fentanyl is mostly metabolized by cytochrome P4503A4. The inter-individual differences of CYP3A4activity or protein content, influencing drug response and toxicity, is one of the main reasons. Our previous research indicated that the genetic polymorphism of CYP3A4*1G could affect the influence of postoperative analgesia with fentanyl. But the mechanism is unclear, and the results of different studies are contradictive. So, the variants of CYP3A4can not completely explain the phenomenon. Pregnane X receptor (PXR) is a key regulator of the expression of CYP3A4in response to endogenous substances and xenobiotics. The polymorphism of PXR*1B haplotype can influence the expression and enzyme activity of CYP3A4. There were no reports about the effect of PXR*1B haplotype(combined with PXR11193T>C and8055C>T) on the enzyme activity of CYP3A4in vivo and postoperative analgesia with fentanyl. We, therefore, investigated PXR*1B haplotype in relation to CYP3A4enzyme activity in vivo and the effect of post-operative analgesia with fentanyl in Chinese patients undergoing gynecologic surgery. Materials and Methods1Patients ProfileA total of102females, of Han nationality, aged20-50yrs, of ASA I or II, and scheduled for abdominal total hysterectomy or myomectomy under general anesthesia were screened. The polymorphic sites of PXR11193T>C,8055C>T were analyzed by the polymerase chain reaction(PCR), direct sequencing. The genotype of PXR*1B were analyzed by PHASE V.2.1software. The patients were assigned to three groups according to the genotypes of PXR11193T>C,8055C>T:wild homozygote group(w/w), mutation heterozygote group(m/w) and mutation homozygote group(m/m). Patients were also divided into three groups by the genotype of PXR*1B haplotype cluster analyzed by PHASE V.2.1software:non-PXR*1B haplotype cluster group, PXR*1B haplotype cluster group and PXR*1B/*1B group.2Anesthetic Procedure and Postoperative Pain AssessmentPatients did not take premedication. Every patient was given standard monitor, including heart rate, blood pressure, pulse, saturation of pulse oxygen, electrocardiography. During the induction of anesthesia, O.lmg/kg midazolam,0.5mg/kg propofol,2μg/kg remifentanil and lmg/kg succinylcholine were injected intravenously. Atracurium0.6mg/kg, as an initial dosage, was administered intravenously immediately after tracheal intubation. Then atracurium was intermittently injected0.1to0.2mg/kg and remifentanil were infused0.1to0.2μg/kg/min and propofol was infused6to8mg/kg/h for maintenance of anesthesia. All patients received PCIA with fentanyl as soon as they were stable and awake. The dose of fentanyl was deliverly recorded. The patients’ pain was assessed with visual analog scale(VAS) as soon as patients were conscious and able to talk. If VAS score>3, the patients were given fentanyl20μg every5min until VAS score≤3,and PCIA with fentanyl was then started. VAS score was maintained less than3. The amount of fentanyl consumed within24hours during PCIA were recorded.PCIA, including1mg fentanyl and5mg droperidol in100ml normal saline, was administered using a computer controlled infusion pump (CADD-Legacy6300), which was programmed to give a2ml bolus of fentanyl solution with a5min lockout time,0.5ml/h background infusion and a maximum of145μg per hour.3Genotyping for PXR polymorphismsPeripheral venous blood samples were taken2ml from all patients. Genomic DNA was extracted using a conventional phenol-chloroform procedure. Genotyping of PXR11196T>C,8055C>T allele was conducted by polymerase chain reaction(PCR), direct sequencing. PXR*1B haplotype was genotyped by PHASE V.2.1software.4Evaluation of CYP3A4activityThe CYP3A4activity was determined by the plasma ratio of1’-hydroxymidazolam(1’-MDZ) to midazolam(MDZ), at the time of1h after intravenous injection of0.1mg/kg midazolam for induction. Liquid chromatography mass spectrometry(LC/MS) was used to measure the level of1’-MDZ and MDZ.5Statistical analysisSPSS17.0software was used for statistical analyses. Values were reported as x±s. Chi-square test was used to verify Hardy-Weinberg equilibrium. Data for the fentanyl consumption were compared using one-way analysis of variance with post hoc Bonferroni correction, Between-group comparisons such as for the VAS score involved the Mann-Whitney test U test. 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. The a was set0.05.Results1General informationAll of102women were included. The VAS pain score immediately postoperatively was(6.0±1.3). At24h after surgery, it was(2.3±0.8). At48h after surgery, it was(1.3±0.3). No one needed rescue management for inadequate pain control. The fentanyl consumption was (370.7±170.9) μg and (190.6±102.6)μg in the first and second24h postoperatively, respectively. The incidence of postoperative nausea and vomiting was7.8%.The incidence of mild sedation and dizzy in our study was2.8%and5.9%, respectively. 2Frequency of PXR111193T>C、PXR8055C>T and PXR*1B haplotypeThe frequency of PXR11193T>C allele in gynecologic patients was48%; The frequency of PXR8055C>T allele was45.6%; The frequency of PXR*1B haplotype was34.8%. Allele frequency was in Hardy-Weinberg equilibrium (P>0.05).3Effect of PXR gene polymorphism on CYP3A4activity and fentanyl analgesic effectThere were no statistical difference in general information, VAS pain scale immediately surgery and at24h,48h after surgery among different groups(P>0.05). There were no significantly statistical difference in the amount of fentanyl consumed within24hours during PCIA among different groups(P>0.05); the enzyme activity of CYP3A4had no significantly statistical variation.There was statistical difference in incidence of dizzy among groups(P<0.05), the incidence of dizzy in PXR*1B group was5.9%, while other groups did not have anyone.Conclusions1The frequency of PXR11193T>C, PXR8055C>T and PXR*1B haplotype were respectively48%,45.6%and34.8%;2The polymorphisms of PXR11193T>C, PXR8055C>T and PXR*1B haplotype have no significant effect on postoperative analgesia with fentanyl.