Genetic Polymorphisms In The MDR1 Gene And The Effects On Analgesia Of Fentanyl

Background and ObjectiveFentanyl is a synthetic opioid widely used for intravenous analgesia. The analgesia effect and the adverse effect of fentanyl varies in different individuals, which makes it difficult to know the appropriate dose for a particular patient. Fentanyl is transported predominantly by P-glycoprotein in the central nervous system after intravenous administration. Interindividual variation of P-glycoprotein expression or activity caused by genetic polymorphisms has been investigated. P-glycoprotein is encoded by MDR1 gene. Genetic variation within the MDR1 gene may contribute to interindividual variability in drug transportation. Single nucleotide polymorphisms (SNPs) are the most common form of genetic variations in the MDRl gene.3435C>T is a high-frequency allele in Chinese, the alteration of function remains unclear in vitro and in vivo. The influence of MDR1C3435T on fentanyl analgesic effect has not been reported. Due to the importance of MDR1 gene in the transportation of fentanyl, we conducted this study to observe the impact of MDR1C3435T 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. Subjects Total one hundred and ninety-six subjects, undergoing selective abdominal total hysterectomy or myomectomy with general anesthesia, aged 20-50 years, within 18.5-24.9 BMI, and having an American Society of Anesthesiologists (ASA) physical status ofⅠorⅡ, were enrolled. Exclusion criteria included the following:known history of psychiatric disease, alcohol or drug abuse, chronic analgesic use, significant cardiovascular disease, hepatic or renal dysfunction, diabetes mellitus, pregnancy or nursing. Subjects who have consumed drugs which are substrates or inhibitors of P-glycoprotein and change fentanyl metabolisms in one month were also excluded. The study design was admitted by Institutional Ethics Committee of Zhengzhou University. The subjects were divided into three groups according to the genotypes.2. Anesthesia and AnalgesiaA standardized, general anesthesia technique was used for all subjects. General anesthesia induction was achieved by 0.1 mg/kg midazolam,0.5 mg/kg propofol,2μg/kg remifentanyl and 1 mg/kg succinylcholine. During the operation, remifentanyl (0.1-0.2μg/kg/min) and propofol (6-8 mg/kg/h) were used for maintenance of anesthesia. 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. The patients'pain was assessed with VAS after consciousness. If VAS score>3, the patients were given fentanyl 20μg every 5 minites until VAS score≤3, and PCIA with fentanyl was then started. The PCIA drug:fentanyl 1.0 mg and droperidol 5 mg in 100 ml saline. The background infusion rate was 0.5 ml/h. The PCIA pump(CADD-Legacy 6300, American) was programmed to allow a 2 ml bolus of fentanyl solution with a 5 minites lockout interval,7 times successful delivery per hour and maximum dosage 145μg per hour. If VAS score>4, the patient was excluded. The fentanyl consumption and occurrence of any adverse effects in the first and second 24 h postoperatively were recorded.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 MDR13435 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 DNA sequence analysis.4. Statistical analysisSPSS 13.0 software was used for statistical analyses, values were reported as x±s. Chi-square test or Fisher exact test was used to verify Hardy-Weinberg equilibrium. One-way analysis of variance was used to assess whether significant differences exist among the three genotypes, after analysis of covariance after justments for BMI, age, remifentanil and propofol consumption in the operation was used to compare the differences among the different genotype groups on the fentanyl consumption; LSD was used to compare the two groups. The incidences of any adverse effects were analyzed using Chi-square test or Fisher exact test.P-values <0.05 were considered statistically significant.Results1. General informationAmong the 196 subjects, the VAS pain score immediately after surgery was 5.6±1.6. It was 2.2±0.8 at 24 h after surgery. The fentanyl consumption was 399.6±214.9μg in the postoperative first 24 h. The incidence of postoperative nausea and vomiting was 25.0%. The incidences of pruritus and mild sedation in our study were 0.5% and 1.5%, respectively.2. Frequency of MDR1C3435T alleleThe frequency of MDR1C3435T allele in gynecologic patients was 36.2%. The allele frequency was in Hardy-Weinberg equilibrium (P>0.05). The allelic frequency of MDR1C3435T in our study was similar to that reported in Chinese healthy volunteers (40.0%) and Han Chinese renal transplant patients (35.8%) (P>0.05).3. MDR1C3435T gene polymorphism and fentanyl analgesic effectAmong the 196 subjects, there were 82 wildtype homozygotes (CC),86 heterozygotes (CT), and 28 mutant homozygotes (TT) for MDR1C3435T. There were no significant differences in general information among the three genotype groups (P>0.05). No statistical difference in postoperative VAS pain scores were detected across genotypes. The amount of fentanyl used within 24 h in CC group is 382.2±214.1μg in CT group is 425.7±222.2μg, and in TT group is 368.6±191.3μg. There was no significant difference in incidences of adverse events among the different genotype groups (P>0.05).Conclusions1. The frequency of MDR1C3435T allele in gynecologic patients is 36.2%;2. MDR1C3435T is a non-functional mutation. MDR1C3435T genetic polymorphism has no effects on the individual variation in patient's responseness to analgesia of fentanyl;3. There is no significant relation between adverse effects of fentanyl and MDR1C3435T polymorphism.