Effect of interleukin 6 –174G>C gene polymorphism on opioid requirements after total hip replacement

The analysis of analgesic treatment was conducted in a group of 196 patients after THR (126 women, 61.2 %), aged from 32 to 86 years (mean 65.1 ± 10.7 years), during the planned 7 days of postoperative hospitalization. The mean body weight in the study group was 77.01 ± 14.56 kg, and the mean body mass index (BMI: kg/m²) was 27.1 ± 4.1. Of 196 study participants, 153 were non-smokers (78.1 %) and 43 (21.9 %) were smokers. The THR procedures were performed by three experienced orthopedic surgeons, via a standardized anterolateral approach using the same non-cemented implant system (Rimcup, Exception, Biomet), and medicated according to multimodal therapy in compliance with postsurgical analgesic treatment recommendations involving oral and/or parenteral analgesics with different mechanisms of action, i.e. opioid analgesics (OP) (morphine, pethidine and tramadol), non-opioid analgesics (acetaminophen and metamizole) and NSAIDs (ketoprofen and diclofenac) [6].

All patients were assessed by a consultant anaesthetist 24 h prior to the operation. To eliminate the impact of pharmacological treatment before the surgery on the results of the present study, all patients received the same type of premedication, 7.5 mg midazolam. Other analgesic administrations in 48 h before THR constituted one of the exclusion criteria. The THR procedure was performed using spinal anaesthesia after implementing routine peri-operative monitoring. Spinal anaesthesia was performed by an experienced consultant anaesthetist, after applying local anaesthetic to skin (2–5 ml of 1 % lidocaine), using the midline approach, with a pencil-point 27G spinal needle. After administration of 2–4 ml of 0.5 % heavy bupivacaine (Marcaine Spinal 0.5 % Heavy) without the use of any adjuvant, the level of the block was established prior to skin incision. The conduct of the spinal anaesthesia was recorded in the anaesthetic chart and was performed at the discretion of the anaesthetist. After the procedure patients were transferred to the postoperative ward and monitored according to local protocol. Each patient was individually observed, and the patient-specific chart of dynamic changes in pain perception was recorded, using the five-level Verbal Rating Scale (VRS). All patients, in the timeframe of 3–6 h after the surgery, were intravenously administered one of two (based on drug-related indications and contraindications) non-opioid analgesics, viz. 1.0 g metamizole or 1.0 g acetaminophen, as recommended by the Polish Association for the Study of Pain [7]. Patients were transferred to the orthopaedic ward immediately after successful pain control, i.e. no pain or mild pain assessed by VRS. The multimodal analgesic treatment after THR was defined by the operating surgeons after considering indications and contraindications to the use of the two groups of drugs (opioid and non-opioid analgesics). Postoperative pain was controlled by the patient-controlled analgesia (PCA) method and VRS during day-time, as well as night-time nurse-controlled analgesia (NCA). The pain intensity was recorded several times a day by a managing physician (at least during morning and evening check visits) or night-shift physician, complemented by recorded patients’ claims of increased pain intensity. In our study, rehabilitation started on the day of surgery, after discharge from the recovery room. To assess pain intensity, the five-level (VRS) was used, where a score of 3–4 was classified as a moderate intensity of pain, and score 5 as severe pain. The selection of opioids and non-opioids was based on the VRS score. In the case of moderate pain intensity (VRS 3–4), a patient was administered a non-opioid analgesic drug, and for high-intensity pain an opioid. All medication adjustments were recorded in the individual patient files. The dose of injectable opioids was converted to injectable morphine dose according to the conversion factors given in the literature: tramadol 10:1 and pethidine 10:1 [8]. For analysis of non-opioid and/or NSAID use, the 0/1 system was applied. The term 1 indicates a day on which non-opioids and/or NSAIDs were taken, whereas a day without medication with those drugs was described as 0. The simplified system was applied, since different drugs were administered (ketoprofen, diclofenac, acetaminophen, metamizole) and no reliable data is available to date for dose equivalence calculations. The above-mentioned medications were administered parenterally (opioids) or orally (non-opioid analgesics and NSAIDs). The analysis of pain relief therapy included information on the drugs applied, mode of dosing (single or multiple), daily dose, route of administration, and drug refusal due to the absence of pain recorded each study day. i.e. on the day of surgery and recovery in postoperative room (day 0), and then daily from day 1 to day 6. The protocol of the study was approved by the Ethics Committee at Pomeranian Medical University (BN-001/6/07), and all patients gave written informed consent.

Genomic DNA was extracted from 200 μL of whole blood samples using Gene-MATRIX Quick Blood DNA Purification Kit (EURx, Poland). Polymorphism rs1800795:G>C in the promoter region of the IL6 gene (–174G>C) was determined using the PCR–RFLP method, as described previously [9], with minor modifications. Briefly, a 299-bp fragment of the IL6 gene was amplified during 35 cycles of PCR (initial denaturation at 95° for 5 min, then 95 °C/59 °C/72 °C, each step for 30 s) with the primer pair: sense primer: 5′-TGT CAA GAC ATG CCA AGT GCT-3′ and antisense: 5′-GCC TCA GAG ACA TCT CCA GT CC-3′. Amplification reactions were performed in a total volume of 12 μL using Mastercycler ep Gradient S (Eppendorf, Germany). The amplification mix contained 0.3 pmol/μL of each primer, 20 ng of genomic DNA, 0.6 U of RedTaq Polymerase (Sigma-Aldrich, Germany) in 1× enzyme-specific buffer (containing magnesium chloride at a final concentration of 1.5 mMol) and deoxynucleoside triphosphates (Sigma-Aldrich), 200 μmol of each. Subsequently, the PCR product was digested with Hin1II endonuclease (ThermoFisher Scientific, Lithuania) at 37 °C and separated on a 4 % agarose gel to distinguish between allele G (227 + 50 + 13 bp) and allele C (118 + 109 + 50 + 13 bp).

The Mann–Whitney test was used to compare opioid doses between genotype groups. The χ ² test and Fisher exact test were used to analyze associations between genotypes or alleles and administration of opioids. Multiple logistic regression was performed to find independent variables associated with the administration of opioids. p < 0.05 was considered significant. Statistica 10 was used for statistical calculations.