Effects of morphine and tramadol on somatic and visceral sensory function and gastrointestinal motility after abdominal surgery

Neuroimmunological complications arising from chemotherapy-induced gut toxicity and opioid exposure in female dark agouti rats

Cancer patients may experience symptom clusters, including chemotherapy-induced (CI) gut toxicity (CIGT) and cognitive impairment. Analgesic selection for pain associated with CIGT is difficult as opioids induce glial reactivity and unwanted side effects. This study quantified central glial reactivity and proinflammatory effects in rats with CIGT using three mechanistically different analgesics. Regional adaptations were indicative of immune-to-brain signaling routes. Utilizing a 5-fluorouracil-induced GT (5IGT) rat model and analgesic intervention (carprofen (CAR), buprenorphine (BUP), and tramadol (TRAM)), spinal and brain neuroimmune modulation was examined via microglial, astrocyte, and proinflammatory (cluster of differentiation molecule 11b; CD11b, glial fibrillary associated protein; GFAP, and interleukin-1 beta; IL1β) reactivity marker expression changes by western blot analysis. 5IGT significantly increased thoracic GFAP (p < 0.05) and IL-1β (p < 0.0001) expression, CAR and BUP ameliorated these effects. BUP and TRAM with 5-FU synergistically increased hippocampal GFAP expression. CAR administered with 5IGT significantly elevated hippocampal and thoracic CD11b expression levels (p < 0.05). The neuroimmune responses observed in this study suggest activation of peripheral-to-central immune signaling pathways. We speculate that the opioid-induced hippocampal changes inferred a humorally mediated mechanism, whereas thoracic neuroimmune modifications indicated activation of an indirect neural route. Although TRAM ameliorated 5IGT-intestinal inflammation, this opioid presents complications relating to bodyweight and regional glial dysregulation (neuroinflammation) and may not be optimal in the management of pain associated with 5IGT. The chemotherapy-induced gut-derived neuroimmune consequences observed suggest a potential mechanistic contribution to central components of the cancer symptom cluster experience, while the opioid-related glial changes have implications for optimal pain management in this setting warranting further investigation.

Local infiltration of tramadol as an effective strategy to reduce post-operative pain: a systematic review protocol and meta-analysis

OBJECTIVE

The purpose of this review is to evaluate the use and effectiveness of the local administration of tramadol in reducing post-operative pain during surgical interventions.

METHODS

The PubMed, EMBASE and Cochrane Central Register of Controlled Trials (CENTRAL) databases will be searched for this review. This systematic review will include studies evaluating the clinical efficacy of the local infiltration of tramadol, with no study design restrictions. Only studies that present clear descriptions of local tramadol administration are published in peer-reviewed journals in the English, Italian, Spanish, French, Portuguese or German language and are published in full will be taken into consideration. A meta-analysis will be performed when there is sufficient clinical homogeneity among the retrieved studies, and only randomized controlled studies and quasi-randomized controlled studies will be included. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach will be used to assess the certainty in the evidence. If a quantitative analysis cannot be conducted, a qualitative description of the results of the retrieved studies will be provided.

RESULTS

A high-quality synthesis of the current evidence on the local administration of tramadol for managing post-surgical pain will be illustrated using subjective reports and objective measures of performance. The primary outcomes will include the magnitude of post-operative pain intensity improvement, with improvement being as defined by a reduction by at least 2 points in the visual analogue scale (VAS) score or numerical rating scale (NRS) score. The secondary outcomes will be the magnitude of reduction in tramadol rescue doses and in other analgesic drug doses.

CONCLUSION

This protocol will present evidence on the efficacy of tramadol in relieving post-surgical pain.

SYSTEMIC REVIEW REGISTRATION

PROSPERO CRD42018087381.

Association between opioid usage and rectal dysfunction in constipation: A cross-sectional study of 2754 patients

BACKGROUND

Opioid use has reached epidemic proportions. In contrast to the known effect of opioids on gut transit, the effect on rectal sensorimotor function has not been comprehensively investigated.

METHODS

Cross-sectional (hypothesis-generating) study of anorectal physiology studies in 2754 adult patients referred to a tertiary unit (2004-2016) for investigation of functional constipation (defined by "derived" Rome IV core criteria). Statistical associations between opioid usage, symptoms, and anorectal physiological variables were investigated. Opioids were sub-classified as prescriptions for mild-moderate or moderate-severe pain.

KEY RESULTS

A total of 2354 patients (85.5%) were classified as non-opioid users, 162 (5.9%) as opioid users for mild-moderate pain, and 238 (8.6%) for moderate-severe pain. Opioids for moderate-severe pain were associated with increased symptomatic severity (Cleveland Clinic constipation score 18.5 vs 15.1; mean difference 2.9 [95%-CI 2.3-3.6]; P < .001), rectal hyposensitivity (odds ratio 1.74 [95%-CI 1.23-2.46]; P = .002), functional evacuation disorders (odds ratio 1.73 [95%-CI 1.28-2.34]; P < .001), and delayed whole-gut transit (odds ratio 1.68 [95%-CI 1.19-2.37]; P = .003). Differences in anorectal variables between opioid users for mild-moderate pain and non-opioid users were not statistically significant. Hierarchical opioid use (non vs mild-moderate vs moderate-severe) was associated with decreasing proportions of patients with no physiological abnormality on testing (40.2% vs 38.1% vs 29.2%) and increasing proportions with both delayed whole-gut transit and rectal sensorimotor dysfunction (16.6% vs 17.5% vs 28.5%).

CONCLUSIONS AND INFERENCES

Opioid use is over-represented in patients referred for investigation of constipation. Opioids for moderate-severe pain are associated with rectal sensorimotor abnormalities. Further studies are required to determine whether this association indicates causation.

Preoperative versus Postoperative Rectus Sheath Block for Acute Postoperative Pain Relief after Laparoscopic Cholecystectomy: A Randomized Controlled Study

Background: Pain after laparoscopic cholecystectomy (LC) is multifactorial and usually not effectively treated. Rectus sheath block (RSB) has been proven to reduce the pain from midline abdominal incision and laparoscopic surgery. We investigated the preemptive analgesic effect of RSB after LC. Methods: In this prospective, randomized, single-center trial, 200 patients undergoing LC were randomized into preoperative RSB (pre-RSB) or postoperative RSB (post-RSB) group. An ultrasound-guided RSB was performed before skin incision in the pre-RSB group or after skin closure in the post-RSB group. The primary outcome was total rescue analgesic consumption at 24 h post-surgery. The secondary outcomes were cumulated rescue analgesic consumption and postoperative pain measured by numerical rating scale (NRS) at 0, 1, 2, 6, 9, 18, and 24 h post-surgery. Results: Total rescue analgesic consumption at 24 h post-surgery was significantly lower in the pre-RSB group than in the post-RSB group (p = 0.020). The cumulated rescue analgesic consumption was significantly lower in the pre-RSB group than in the post-RSB group at 1 h (p = 0.023), 9 h (p = 0.020) and 18 h (p = 0.002) post-surgery. NRS was significantly lower in the pre-RSB group than in the post-RSB group at 0 h post-surgery (p = 0.023). Conclusion: The pre-RSB reduced the analgesic requirements in patients undergoing LC compared with the post-RSB.

Comparison of different sufentanil-tramadol combinations for pain relief within the first 24 hours after cesarean section: a retrospective study

Introduction

Postcesarean section pain management is important for both the mother and the newborn. This study compared the analgesic effects and incidence of adverse events associated with intravenous patient-controlled analgesia (iv-PCA), using different sufentanil–tramadol combinations for postoperative pain control.

Methods

Parturients (n=5,794) who had been scheduled for cesarean section under neuraxial anesthesia and had received iv-PCA between September 2013 and March 2017 were retrospectively analyzed. These patients were assigned to three groups, based on different sufentanil–tramadol combinations: ST1 (n=1,347), ST2 (n=2,401), and ST3 (n=2,046). The analgesic efficacy, total drug consumption, and incidence of adverse effects within 24 hours after surgery were compared among the three groups.

Results

The ST3 group had lower visual analog scale pain scores at rest and with movement at all time points during the first 24 hours postoperatively than the other two groups (P<0.01, Bonferroni corrected). The sufentanil dosage administered to the ST3 group was lower, and the tramadol dosage was higher than those administered to the other groups within 24 hours after surgery (P<0.01, Bonferroni corrected). Moreover, all parturients scored 2 points on the Ramsay sedation scale. Adverse reactions such as pruritus and respiratory depression were not observed in any group. No significant differences were noted in the incidence of nausea/vomiting, abdominal distension, and dizziness among the three groups (P>0.05).

Conclusion

The visual analog scale scores for postoperative pain decreased as the concentrations of sufentanil and tramadol administered in iv-PCA moderately increased over 24 hours after surgery. This analgesic strategy resulted in a significant reduction in the total sufentanil requirement without increasing the incidence of adverse effects.

Modified dachengqi tang improves decreased gastrointestinal motility in postoperative esophageal cancer patients

OBJECTIVE

To investigate the clinical effects of modified dachengqi tang (DCQT) on promoting gastrointestinal motility in post-operative esophageal cancer patients.

METHODS

Sixty postoperative esophageal cancer patients were enrolled and randomly assigned to the modified treatment group or the control group (30 patients in each group). Patients in the treatment group were given DCQT made from decocted herbs and administered via nasojejunal tube at a dosage of 150 mL. Gastrointestinal motility was assessed by recording time for recovery of bowel sounds, flatus, defecation, and the total amount of gastric drainage during the first three postoperative days. Plasma motilin (MTL) and vasoactive intestinal peptide (VIP) were measured one hour before and three days after surgery.

RESULTS

Compared with the control group, the times to first bowel sound, flatus, and defecation were significantly shorter and there was less gastric drainage in the treatment group (P < 0.01, P < 0.01, P < 0.01, and P < 0.05, respectively). In the treatment group, postoperative plasma MTL was significantly higher (P < 0.01) and VIP was significantly lower than those in the control group (P < 0.05). There was no difference found in either MTL or VIP from before to after operation in the treatment group (P > 0.05). MTL was significantly lower and VIP was higher postoperatively in the control group, compared to before surgery (P < 0.01).

CONCLUSION

Modified DCQT effectively improved decreased gastrointestinal motility in postoperative esophageal cancer patients by increasing MTL and reducing VIP.

Effect of the CYP2D6 gene polymorphism on postoperative analgesia of tramadol in Han nationality nephrectomy patients

OBJECTIVE

Tramadol is a synthetic opioid which has analgesic efficacy in the postoperative pain. It is metabolized by polymorphic enzyme cytochrome P450 (CYP2D6). Patients with different CYP2D6 genotypes would have different responses to tramadol in pain relief. The CYP2D6*10 allele is the most common allele in a Chinese population. The aim of this study was to evaluate whether the different CYP2D6*10 genotypes have an effect on the postoperative tramadol analgesia in the Chinese population after elective nephrectomy.

METHODS

One hundred and twenty patients after performed elective nephrectomy were enrolled in this study after being approved by the local Ethics Committee. The patients were given patient-controlled analgesia (PCA) which included 10 mg/ml tramadol after receiving a loading dose of 100 mg tramadol and 1 mg granisetron intravenously. Blood samples were collected after induction of anesthesia. The CYP2D6*10 polymorphism was analyzed by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). According to the results, the patients were divided into three groups (CYP2D6*1/*1, n = 33; CYP2D6*1/*10, n = 28; CYP2D6*10/*10, n = 50). The total consumption of tramadol, visual analogue scale (VAS) score, and PCA control times among the three genotype groups for 2, 4, 24, 48, and 72 h after operation were compared.

RESULTS

Nine out of 120 patients were dropped out of the study; 111 patients completed the study. The frequency of CYP2D6*10 allele was 57.7%. The demographic data among the three groups were comparable. The consumption of tramadol, patient self-control times of pump, and VAS score in CYP2D6*10/*10 group were significantly higher than that in CYP2D6*1/*1 or CYP2D6*1/*10 group at 2 and 4 h (P < 0.05), while it did not differ between CYP2D6*1/*1 and CYP2D6*1/*10 group (P > 0.05). There was no difference in the incidence of nausea and vomiting among the three groups (P > 0.05). No sever apnea was recorded in these groups.

CONCLUSIONS

Different CYP2D6*10 genotypes have an influence on the analgesic effect of tramadol in Han nationality patients after elective nephrectomy.

Systematic mechanism-orientated approach to chronic pancreatitis pain

Pain in chronic pancreatitis (CP) shows similarities with other visceral pain syndromes (i.e., inflammatory bowel disease and esophagitis), which should thus be managed in a similar fashion. Typical causes of CP pain include increased intrapancreatic pressure, pancreatic inflammation and pancreatic/extrapancreatic complications. Unfortunately, CP pain continues to be a major clinical challenge. It is recognized that ongoing pain may induce altered central pain processing, e.g., central sensitization or pro-nociceptive pain modulation. When this is present conventional pain treatment targeting the nociceptive focus, e.g., opioid analgesia or surgical/endoscopic intervention, often fails even if technically successful. If central nervous system pain processing is altered, specific treatment targeting these changes should be instituted (e.g., gabapentinoids, ketamine or tricyclic antidepressants). Suitable tools are now available to make altered central processing visible, including quantitative sensory testing, electroencephalograpy and (functional) magnetic resonance imaging. These techniques are potentially clinically useful diagnostic tools to analyze central pain processing and thus define optimum management approaches for pain in CP and other visceral pain syndromes. The present review proposes a systematic mechanism-orientated approach to pain management in CP based on a holistic view of the mechanisms involved. Future research should address the circumstances under which central nervous system pain processing changes in CP, and how this is influenced by ongoing nociceptive input and therapies. Thus we hope to predict which patients are at risk for developing chronic pain or not responding to therapy, leading to improved treatment of chronic pain in CP and other visceral pain disorders.

Transcutaneous electrical nerve stimulation attenuates postsurgical allodynia and suppresses spinal substance P and proinflammatory cytokine release in rats

BACKGROUND

Transcutaneous electrical nerve stimulation (TENS) is often used for management of chronic pain.

OBJECTIVE

The purpose of this study was to investigate whether TENS altered postincisional allodynia, substance P, and proinflammatory cytokines in a rat model of skin-muscle incision and retraction (SMIR).

DESIGN

This was an experimental study.

METHODS

High-frequency (100-Hz) TENS therapy began on postoperative day 3 and was administered for 20 minutes daily to SMIR-operated rats by self-adhesive electrodes delivered to skin innervated via the ipsilateral dorsal rami of lumbar spinal nerves L1-L6 for the next 27 days. The expressions of substance P, tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), and interleukin-1beta (IL-1β) in the spinal cord and mechanical sensitivity to von Frey stimuli (4g and 10g) were evaluated.

RESULTS

The SMIR-operated rats displayed a marked hypersensitivity to von Frey stimuli on postoperative day 3. In contrast to the SMIR-operated rats, SMIR-operated rats after TENS administration showed a quick recovery of mechanical hypersensitivity. On postoperative days 3, 16, and 30, SMIR-operated rats exhibited an upregulation of substance P and cytokines (TNF-α, IL-6, and IL-1β) in the spinal cord, whereas SMIR-operated rats after TENS therapy inhibited that upregulation. By contrast, the placebo TENS following SMIR surgery did not alter mechanical hypersensitivity and the levels of spinal substance P, TNF-α, IL-6, and IL-1β.

LIMITATIONS

The experimental data are limited to animal models and cannot be generalized to postoperative pain in humans.

CONCLUSIONS

The results revealed that TENS attenuates prolonged postoperative allodynia following SMIR surgery. Increased levels of spinal substance P and proinflammatory cytokines, activated after SMIR surgery, are important in the processing of persistent postsurgical allodynia. The protective effect of TENS may be related to the suppression of spinal substance P and proinflammatory cytokines in SMIR-operated rats.

The effect of ondansetron on the efficacy of postoperative tramadol: a systematic review and meta-analysis of a drug interaction

Several studies have investigated the presence of a drug interaction between tramadol and ondansetron that reduced the efficacy of tramadol postoperatively. Most of these studies were small and the results inconsistent, so we performed a systematic review and meta-analysis of randomised controlled trials comparing the cumulative dose of tramadol administered by patient-controlled analgesia within the first 24 h after surgery between subjects receiving tramadol alone and those who received tramadol with ondansetron. Six studies, with a total of 340 participants, met the selection criteria and were included in the meta-analysis. There was an increased tramadol requirement in patients receiving ondansetron. The standardised mean difference in tramadol requirements, expressed in terms of standard deviations (95% CI), was 1.03 (0.54-1.53) (p < 0.001) at 4 h, 0.66 (0.06-1.25) (p = 0.03) at 8 h, 0.86 (0.41-1.31) (p < 0.001) at 12 h and 0.45 (0.01-0.90) (p = 0.046) at 24 h postoperatively, where the mean pooled standard deviations were 79.5, 157.7, 238.1 and 289.4 mg at 4, 8, 12 and 24 h, respectively. There was a significant linear time effect over the 24 h, indicating that the effect of ondansetron on tramadol consumption diminished with time. The results support the presence of a drug interaction between tramadol and ondansetron in the early postoperative period that potentially decreases the effectiveness of tramadol.

Pharmacokinetics of tramadol after subcutaneous administration in a critically ill population and in a healthy cohort

Background

Tramadol is an atypical centrally acting analgesic agent available as both oral and parenteral preparations. For patients who are unable to take tramadol orally, the subcutaneous route of administration offers an easy alternative to intravenous or intramuscular routes. This study aimed to characterise the absorption pharmacokinetics of a single subcutaneous dose of tramadol in severely ill patients and in healthy subjects.

Methods/design

Blood samples (5 ml) taken at intervals from 2 minutes to 24 hours after a subcutaneous dose of tramadol (50 mg) in 15 patients (13 male, two female) and eight healthy male subjects were assayed using high performance liquid chromatography. Pharmacokinetic parameters were derived using a non-compartmental approach.

Results

There were no statistically significant differences between the two groups in the following parameters (mean ± SD): maximum venous concentration 0.44 ± 0.18 (patients) vs. 0.47 ± 0.13 (healthy volunteers) mcg/ml (p = 0.67); area under the plasma concentration-time curve 177 ± 109 (patients) vs. 175 ± 75 (healthy volunteers) mcg/ml*min (p = 0.96); time to maximum venous concentration 23.3 ± 2 (patients) vs. 20.6 ± 18.8 (healthy volunteers) minutes (p = 0.73) and mean residence time 463 ± 233 (patients) vs. 466 ± 224 (healthy volunteers) minutes (p = 0.97).

Conclusions

The similar time to maximum venous concentration and mean residence time suggest similar absorption rates between the two groups. These results indicate that the same dosing regimens for subcutaneous tramadol administration may therefore be used in both healthy subjects and severely ill patients.

Trial registration

ACTRN12611001018909

Pharmacokinetics and physiological effects of repeated oral administrations of tramadol in horses

This study evaluated the pharmacokinetics and physiological effects of tramadol during repeated oral administrations in horses. Nine adult healthy horses were administered tramadol at 5 and 10 mg/kg orally every 12 h for 5 days in a randomized, crossover design with a 3-week washout between treatments. Plasma concentrations of tramadol, O- and N-desmethyltramadol (M1 and M2) were measured using Liquid-Chromatography-Mass Spectrometry at predetermined time points following each tramadol administration. Cardiovascular, respiratory and gastrointestinal physiological variables were monitored and adverse events were recorded. Data were analysed with two-way repeated measures anova or Kruskal-Wallis one-way anova on ranks with P < 0.05 considered statistically significant. There were no significant effects of tramadol on the physiological variables. One horse receiving 10 mg/kg tramadol developed mild colic. Following tramadol at 5 and 10 mg/kg, respectively, maximum plasma concentrations (Cmax ) of tramadol ranged from 82-587 and 127-1280 ng/mL, nonconjugated M1 ranged from 2.51-26.7 and 4.88-34.3 ng/mL, and nonconjugated M2 from 12.5-356 and 35.4-486 ng/mL. Corresponding minimum plasma concentrations (Cmin ) of tramadol at 12 h following each dose ranged from 0.8-24 and 3-117 ng/mL. Tramadol accumulated considerably over time, more markedly when given at 10 mg/kg than at 5 mg/kg (accumulation indexes of 3.51 and 1.73 respectively). There was no accumulation of M1 but substantial accumulation of M2. In conclusion, there was accumulation and increase in exposure to tramadol and M2, but not M1, during repeated oral administrations in horses.

Effect of intrathecal magnesium in the presence or absence of local anaesthetic with and without lipophilic opioids: a systematic review and meta-analysis

Spinal anaesthesia is the primary anaesthetic technique for many types of surgery. Adjuncts to the local anaesthetics (LA) used in spinal anaesthesia can exhibit undesirable side-effects, limiting their use, but magnesium may have advantages in this respect. We sought randomized control trials (RCTs) in patients undergoing all types of surgery and in women in labour to compare the effect of intrathecal magnesium sulphate ± LA ± lipophilic opioid (experimental group) with the use of either intrathecal lipophilic opioids ± LA or LA only (control group). The primary outcome was the duration of spinal anaesthesia. Secondary outcomes were: onset and time to maximal sensory blockade, onset of motor block, and duration of sensory and motor blockade. We found 15 RCTs comprising 980 patients. The duration of spinal anaesthesia was significantly increased in the experimental group [standardized mean difference (SMD) -1.05 (-1.70, -0.41) (P = 0.001)], compared with the control group. This increased duration of spinal anaesthesia was seen in non-obstetric studies, SMD -1.38 (-2.11, -0.66) (P = 0.0002), but not in obstetric studies, SMD -0.55 (-1.87, 0.77) (P = 0.41). There was no delay in the onset of sensory or motor blockade. The incidence of hypotension and pruritus was similar in both groups. Heterogeneity was high in all outcome measures. The duration of spinal anaesthesia may be increased by the addition of magnesium to lipophilic opioids ± LA.

The Spanish Pancreatic Club's recommendations for the diagnosis and treatment of chronic pancreatitis: part 2 (treatment)

Chronic pancreatitis (CP) is a complex disease with a wide range of clinical manifestations. This range comprises from asymptomatic patients to patients with disabling symptoms or complications. The management of CP is frequently different between geographic areas and even medical centers. This is due to the paucity of high quality studies and clinical practice guidelines regarding its diagnosis and treatment. The aim of the Spanish Pancreatic Club was to give current evidence-based recommendations for the management of CP. Two coordinators chose a multidisciplinary panel of 24 experts on this disease. These experts were selected according to clinical and research experience in CP. A list of questions was made and two experts reviewed each question. A draft was later produced and discussed with the entire panel of experts in a face-to-face meeting. The level of evidence was based on the ratings given by the Oxford Centre for Evidence-Based Medicine. In the second part of the consensus, recommendations were given regarding the management of pain, pseudocysts, duodenal and biliary stenosis, pancreatic fistula and ascites, left portal hypertension, diabetes mellitus, exocrine pancreatic insufficiency, and nutritional support in CP.

Pain management in laparoscopic donor nephrectomy: a review

The management of postoperative pain is a key to patient early recovery, in particular, where the surgery was performed to benefit another human being. In recent years it has been recognized that multimodal analgesic methods are superior for postoperative pain relief. It is also imperative to remember that inadequately managed acute postoperative pain opens the doorway to possible suffering from chronic postoperative pain later. Although the laparoscopic donor nephrectomy has reduced the disincentives associated with open surgery, still significant percentage of donors suffers from postoperative pain. In the UK, patient-controlled analgesic system (PCAS) using morphine for postoperative pain relief is being used in majority of the transplant centres. Though opioids provide good analgesia, they are far from being an ideal analgesic due to their adverse effects. This paper pragmatically looks in depth on different modalities of pain management in patients undergoing laparoscopic live donor nephrectomy.

Local infiltrative anesthetic effect of tramadol compared to lidocaine for excision of cutaneous lesions: pilot randomized, double-blind clinical study

BACKGROUND

In this double-blind, randomized study, the efficacy of tramadol, an atypical opioid, was tested versus lidocaine in excision of cutaneous lesions of the face.

METHODS

Eighty-eight patients were randomly assigned to receive either 2 mg/kg tramadol 2% plus adrenaline 1:200,000 (group T, n  =  46) or 3 mg/kg lidocaine 2% plus adrenaline 1:200,000 (group L, n  =  42) for excision of cutaneous lesions. Pain at the injection site, 2 and 20 minutes postinjection and 3, 6, and 12 hours postoperatively, was monitored on a 0 to 10 numerical rating scale (NRS). Irritation at the injection point and the duration of postoperative analgesia were also recorded.

RESULTS

There were no significant differences in demographic data, topography, size of the lesions removed, and operative time between the two groups. A tendency toward lower injection NRS pain scores was observed in group L compared to group T (p  =  .064). No statistically significant differences between the two groups were found at 2 and 20 minutes postinjection (p  =  .741 and p  =  .142, respectively); however, pain scores were significantly higher in group L at 3, 6, and 12 hours postoperatively (all p < .001). Erythema at the injection site was observed in nine group T and two group L patients (p  =  .076). No postoperative analgesics were required in the tramadol group of patients, whereas acetaminophen with or without codeine was administered in all but five lidocaine group patients during the first 12 hours.

CONCLUSION

Tramadol may be used as a reliable local anesthetic agent, providing longer postoperative analgesia compared to lidocaine; however, it bears a higher incidence of irritation at the injection site.

Human experimental pain models for assessing the therapeutic efficacy of analgesic drugs

Pain models in animals have shown low predictivity for analgesic efficacy in humans, and clinical studies are often very confounded, blurring the evaluation. Human experimental pain models may therefore help to evaluate mechanisms and effect of analgesics and bridge findings from basic studies to the clinic. The present review outlines the concept and limitations of human experimental pain models and addresses analgesic efficacy in healthy volunteers and patients. Experimental models to evoke pain and hyperalgesia are available for most tissues. In healthy volunteers, the effect of acetaminophen is difficult to detect unless neurophysiological methods are used, whereas the effect of nonsteroidal anti-inflammatory drugs could be detected in most models. Anticonvulsants and antidepressants are sensitive in several models, particularly in models inducing hyperalgesia. For opioids, tonic pain with high intensity is attenuated more than short-lasting pain and nonpainful sensations. Fewer studies were performed in patients. In general, the sensitivity to analgesics is better in patients than in healthy volunteers, but the lower number of studies may bias the results. Experimental models have variable reliability, and validity shall be interpreted with caution. Models including deep, tonic pain and hyperalgesia are better to predict the effects of analgesics. Assessment with neurophysiologic methods and imaging is valuable as a supplement to psychophysical methods and can increase sensitivity. The models need to be designed with careful consideration of pharmacological mechanisms and pharmacokinetics of analgesics. Knowledge obtained from this review can help design experimental pain studies for new compounds entering phase I and II clinical trials.

Analgesic effects of tramadol during panretinal photocoagulation

Purpose

To evaluate the effectiveness of tramadol for the reduction of pain in panretinal photocoagulation (PRP).

Methods

A double-masked randomized controlled study was performed. Fifty-eight eyes in 29 patients with proliferative diabetic retinopathy were enrolled. The eyes of the patients were randomized into two groups. Group A received an empty capsule. Group B received an oral intake of 100 mg tramadol. The capsule used in Group A had the same appearance as that used in Group B. Pain during PRP was assessed using a visual analog scale. Vital signs, including blood pressure and heart rate, were measured.

Results

The mean pain scores for groups A and B were 4.80±2.10 and 3.83±1.82 (p=0.09). There were no significant differences in the mean pain scores between the two groups. More patients in group A complained of greater pain than moderate intensity (visual analogue scale=4). Systemic blood pressure increased significantly in group A after laser treatment. However, there were no significant differences in the diastolic blood pressure changes between the two groups. We found no statistical correlation in the heart rate changes.

Conclusions

We failed to prove that tramadol is effective for pain relief because of the small sample size. However, tramadol was effective for the relief of more severe pain. It was also found to stabilize vital sign changes, such as systolic blood pressure during PRP.

[Systemic analgesia for postoperative pain management in the adult]

Severe postsurgical pain contributes to prolonged hospital stay and is also believed to be a risk factor for the development of chronic pain. Locoregional anesthesia, which results in faster patient recovery with fewer side effects, is favored wherever feasible, but is not applicable to every patient. Systemic analgesics are the most widely used method for providing pain relief in the postoperative period. Improvements in postoperative systemic analgesia for pain management should be applied and predictive factors for severe postoperative pain should be anticipated in order to control pain while minimizing opioid side effects. Predictive factors for severe postoperative pain include severity of preoperative pain, prior use of opiates, female gender, non-laparoscopic surgery, and surgeries involving the knee and shoulder. Pre- and intraoperative use of small doses of ketamine has a preventive effect on postoperative pain. Multimodal or balanced analgesia (the combined use of various analgesic agents) such as NSAID/morphine, NSAID/nefopam, morphine/ketamine improves analgesia with morphine-sparing effects. Nausea and vomiting, the principle side effects of morphine, can be predicted using Apfel's simplified score; patients with a high Apfel score risk should receive preemptive antiemetic agents aimed at different receptor sites, such as preoperative dexamethasone and intraoperative droperidol. Droperidol can be combined with morphine for postoperative patient-controlled anesthesia (PCA). When PCA is used, dosage parameters should be adjusted every day based on pain evaluation. Patients with presurgical opioid requirements will require preoperative administration of their daily opioid maintenance dose before induction of anesthesia: PCA offers useful options for effective postsurgical analgesia using a basal rate equivalent to the patient's hourly oral usage plus bolus doses as required.

Is the pain in chronic pancreatitis of neuropathic origin? Support from EEG studies during experimental pain

AIM: To prove the hypothesis that patients with chronic pancreatitis would show increased theta activity during painful visceral stimulation.

METHODS: Eight patients and 12 healthy controls underwent an experiment where the esophagus was electrically stimulated at the pain threshold using a nasal endoscope. The electroencephalogram (EEG) was recorded from 64 surface electrodes and “topographic matching pursuit” was used to extract the EEG information in the early brain activation after stimulation.

RESULTS: A major difference between controls and patients were seen in delta and theta bands, whereas there were only minor differences in other frequency bands. In the theta band, the patients showed higher activity than controls persisting throughout the 450 ms of analysis with synchronous brain activation between the channels. The main theta components oscillated with 4.4 Hz in the patients and 5.5 Hz in the controls. The energy in the delta (0.5-3.5 Hz) band was higher in the controls, whereas the patients only showed scattered activity in this band.

CONCLUSION: The differences in the theta band indicate that neuropathic pain mechanisms are involved in chronic pancreatitis. This has important implications for the understanding and treatment of pain in these patients, which should be directed against drugs with effects on neuropathic pain disorders.

Co-administration of rofecoxib and tramadol results in additive or sub-additive interaction during arthritic nociception in rat

Over the decades, nonsteroidal anti-inflammatory drugs (NSAIDs) and opioids are the most commonly used analgesics in the management of acute and chronic pain. In order to assess a possible antinociceptive interactions, the antinociceptive effects of rofecoxib p.o., a preferential inhibitor of cyclooxygenase-2, and tramadol-hydrochloride p.o., an atypical opioid analgesic, administered either separately or in combination, were determined using a rat model of arthritic pain. The data were interpreted using the surface of synergistic interaction (SSI) analysis and an isobolographic analysis to establish the nature of the interaction. The SSI was calculated from the total antinociceptive effect produced by the combination after subtraction of the antinociceptive effect produced by each individual drug. Female rats received orally rofecoxib alone (1.0, 1.8, 3.2, 5.6, 10.0, 17.8, 31.6 and 56.2 mg/kg), tramadol alone (1.8, 3.2, 5.6, 10.0, 17.8, 31.6 and 56.2 mg/kg) or 12 different combinations of rofecoxib plus tramadol. Five combinations exhibited various degrees of sub-additive (i.e. less than the sum of the effects produced by the each drug alone) antinociceptive effects (3.2 mg/kg tramadol with 7.8 mg/kg rofecoxib; 5.6 mg/kg tramadol with either 10.0 or 17.8 mg/kg rofecoxib; 10.0 mg/kg tramadol with either 10.0 or 17.8 mg/kg rofecoxib), whereas the other 7 combinations showed additive antinociceptive effects (i.e. the sum of the effects produced by each agent alone). Three combination of rofecoxib+tramadol (10.0+5.6, 10.0+10.0, and 17.8+5.6 mg/kg respectively) presented high sub-additive interactions (P<0.002: Q=9.5). The combination rofecoxib (17.8 mg/kg)+tramadol (10.0 mg/kg) caused gastric injuries less severe than those observed with indomethacin, but more severe than those obtained with rofecoxib or tramadol in single administration. The antinociceptive interaction of rofecoxib and tramadol suggests that combinations with these drugs may have no clinical utility in pain therapy.

The enantiomers of tramadol and its major metabolite inhibit peristalsis in the guinea pig small intestine via differential mechanisms

Background

Inhibition of intestinal peristalsis is a major side effect of opioid analgesics. Although tramadol is an opioid-like analgesic, its effect on gut motility is little known. Therefore, the effect of (+)-tramadol, (-)-tramadol and the major metabolite O-desmethyltramadol on intestinal peristalsis in vitro and their mechanisms of action were examined. Distension-induced peristalsis was recorded in fluid-perfused segments of the guinea pig small intestine. The intraluminal peristaltic pressure threshold (PPT) was used to quantify the motor effects of extraserosally administered drugs.

Results

Racemic tramadol, its (+)- and (-)-enantiomers and the major metabolite O-desmethyltramadol (0.1 – 100 μM) concentration-dependently increased PPT until peristalsis was transiently or persistently abolished. The rank order of potency was (-)-tramadol < (+)-tramadol <O-desmethyltramadol. The peristaltic motor inhibition caused by (+)- and (-)-tramadol was markedly and that of O-desmethyltramadol nearly completely prevented by naloxone, but left unaltered by the 5-hydroxytryptamine receptor antagonists methysergide plus tropisetron. The adrenoceptor antagonists prazosin plus yohimbine reduced the effect of (+)- and (-)-tramadol but not that of O-desmethyltramadol.

Conclusion

The results show that the metabolite O-desmethyltramadol is more potent in inhibiting peristalsis than its parent compound. The action of all tramadol forms depends on opioid receptors, and that of (+)- and (-)-tramadol also involves adrenoceptors.

Postoperative effects of opioid analgesics administered via continuous perfusion and patient controlled analgesia after open heart surgery

Critical care nurses and physicians are familiar with the principles of patient controlled analgesia and the opioid analgesics' regimens and observations necessary for pain control in the postoperative cardiac surgical patients. The objective of the study was to compare the effects of morphine, fentanyl, meperidine, remifentanil and tramadol which were administered by patient controlled analgesia and continuous intravenous infusion combination on the various parameters. This study was designed as prospective randomised trial. Fifty patients undergone open heart surgery with sternotomy were entered equally into five randomized groups. Visual analog scale was used by researcher nurse to assess the patient' pain status. Respiratory rate, heart rate and blood gases (pO2, pCO2, SaO2), radial arterial blood pressures were measured in the first 24 hrs postoperatively. Bolus requirements were determined by physicians and side effects of the analgesics were documented. Fentanyl group showed statistically higher levels of mean pO2 (p=0.002). Meperidine had the lowest number of bolus doses (p=0.001). There were no significant differences between the groups for pain management except higher visual analog scales on tramadol. Headache, stomach-ache and, palpitations were observed in our patients. Remifentanil, meperidine, fentanyl and morphine showed similar effect with each other for pain relief except tramadol.

Effect of the CYP2D6*10 C188T polymorphism on postoperative tramadol analgesia in a Chinese population

OBJECTIVE

The CYP2D6*10 allele is the most common allele with a frequency ranging from 51.3 to 70% and correlated with a significantly reduced metabolic activity in a Chinese population. The aim of the present study was to investigate whether the CYP2D6*10 allele has an impact on the postoperative analgesia effect of tramadol in Chinese patients recovering from major abdominal surgery.

METHODS

A prospective study design was used and 70 gastric cancer patients recovering from gastrectomy were enrolled. After receiving a loading dose i.v., patients could self-administer doses of the drug combination (10 mg/ml tramadol plus 0.3 mg/ml metoclopramide) via patient-controlled analgesia (PCA). Blood samples were collected after induction of anesthesia. The CYP2D6*10 C188T polymorphism was analyzed by means of polymerase chain reaction-based restriction fragment length polymorphism (PCR-RFLP). Demographic data among groups with different genotypes were analyzed using analysis of variance. The total consumption of tramadol between the three genotype groups for 48 h was compared.

RESULTS

The allele frequency of CYP2D6*10 is 52.4%; patients were categorized into three groups according to the CYP2D6 genotype: patients without CYP2D6*10 (group I, n=17), patients heterozygous for CYP2D6*10 (group II, n=26), and patients homozygous for CYP2D6*10 (group III, n=20). The demographic data among the three groups were comparable. The total consumption of tramadol for 48 h in group III was significantly higher than that in groups I and II, while it did not differ between groups I and II.

CONCLUSIONS

This study indicates that the CYP2D6*10 allele has significant impact on analgesia with tramadol in a Chinese population. Pharmacogenetics may explain some of the varying responses to pain medication in postoperative patients.

The effects of tramadol and fentanyl on gastrointestinal motility in septic rats

In this study, we investigated the effects of tramadol and fentanyl on gastrointestinal transit (GIT) during acute systemic inflammation in an experimental model of cecal ligation and perforation (CLP). One-hundred-twenty male Swiss-Albino rats were divided randomly into 6 groups: Group I = sham-operated + saline; Group II = sham-operated + fentanyl; Group III = sham-operated + tramadol; Group IV = CLP + saline; Group V = CLP + fentanyl; Group VI = CLP + tramadol. Suspension of charcoal was administered as an intragastric meal to measure the GIT. GIT% (mean +/- sd) were 46.1% +/- 9.8%, 43.2% +/- 9.8%, 45.9% +/- 10.2%, 33.2% +/- 9.2%, 24.9% +/- 4.1%, and 31.8% +/- 8.4% in Groups I, II, III, IV, V, and VI, respectively. GIT% was significantly less in Group V than in Groups I, II, III, and IV (P < 0.05). The Group VI mean value was significantly lower than those of Groups I, II, and III (P < 0.05) but not different from those of Groups IV and V (P > 0.05). The antitransit effect of fentanyl was shown to have increased in the experimental sepsis model, but no decrease in GIT was obtained with tramadol. This was thought to be the result of an associated endogenic opioid system activation and receptor upregulation in sepsis.

A placebo-controlled randomized clinical trial of perioperative administration of gabapentin, rofecoxib and their combination for spontaneous and movement-evoked pain after abdominal hysterectomy

Current treatments for post-injury movement-evoked pain are inadequate. Non-opioids may complement opioids, which preferentially reduce spontaneous pain, but most have incomplete efficacy as single agents. This trial evaluates efficacy of a gabapentin-rofecoxib combination following hysterectomy. In addition to IV-PCA morphine, 110 patients received either placebo, gabapentin (1800 mg/day), rofecoxib (50 mg/day) or a gabapentin-rofecoxib combination (1800/50 mg/day) starting 1 h pre-operatively for 72 h. Outcomes included pain at rest, evoked by sitting, peak expiration and cough, morphine consumption and peak expiratory flow (PEF). For placebo, gabapentin, rofecoxib and combination, 24 h pain (100 mm VAS) was: at rest-23.6 (P<0.05 vs. all treatments), 13.8, 14.4 and 12.1; during cough-50.7 (P<0.05 vs. all treatments), 41.5, 44.8 and 30.8; 48 h morphine consumption (mg) was: 130.4 (P<0.05 vs. all treatments), 81.7, 75.6 and 57.2 (P<0.05 vs. gabapentin and rofecoxib) and 48 h PEF (% baseline) was: 63.9 (P<0.05 vs. all treatments), 77.2, 76.7 and 87.5 (P<0.05 vs. gabapentin and rofecoxib). Adverse effects were similar in all groups except sedation which was more frequent with gabapentin. Combination and rofecoxib reduced pain interference with movement, mood and sleep (P<0.05) and combination was superior to gabapentin for all these three (P<0.05). These data suggest that a gabapentin-rofecoxib combination is superior to either single agent for postoperative pain. Other benefits include opioid sparing, reduced interference with movement, mood and sleep and increased PEF suggesting accelerated pulmonary recovery. Future research should identify optimal dose-ratios for this and other analgesic combinations.

The median effective dose of tramadol and morphine for postoperative patients: a study of interactions

Tramadol is a centrally-acting analgesic drug. In a search of an effective balanced analgesia technique with a morphine-sparing component, we studied the median effective analgesic doses (ED(50)) of tramadol, morphine, and their combination to determine the nature of their interaction using an isobolographic analysis. In this double-blind, randomized, two-stage prospective study, 90 postoperative patients were enrolled in one of three groups. The dose of tramadol and morphine received by a particular patient was determined using an up-down allocation technique. Initial doses and increments were, respectively, 100 mg and 10 mg in the tramadol group and 5 mg and 1 mg in the morphine group. In the second part, a 40:3 tramadol:morphine dosing ratio was used. The threshold of effective analgesia was defined as 3 or less on a numerical pain score (0-10). Isobolographic analysis was subsequently applied. The ED(50) values (95% confidence interval) of tramadol and morphine were, respectively, 86 mg (57-115 mg) and 5.7 mg (4.2-7.2 mg). The ED(50) of the combination was 72 mg (62-82 mg) for tramadol and 5.4 mg (4-6.6.2 mg) for morphine. The combination of tramadol and morphine was infra-additive and thus not recommended for postoperative analgesia.

Clinical pharmacology of tramadol

Tramadol, a centrally acting analgesic structurally related to codeine and morphine, consists of two enantiomers, both of which contribute to analgesic activity via different mechanisms. (+)-Tramadol and the metabolite (+)-O-desmethyl-tramadol (M1) are agonists of the mu opioid receptor. (+)-Tramadol inhibits serotonin reuptake and (-)-tramadol inhibits norepinephrine reuptake, enhancing inhibitory effects on pain transmission in the spinal cord. The complementary and synergistic actions of the two enantiomers improve the analgesic efficacy and tolerability profile of the racemate. Tramadol is available as drops, capsules and sustained-release formulations for oral use, suppositories for rectal use and solution for intramuscular, intravenous and subcutaneous injection. After oral administration, tramadol is rapidly and almost completely absorbed. Sustained-release tablets release the active ingredient over a period of 12 hours, reach peak concentrations after 4.9 hours and have a bioavailability of 87-95% compared with capsules. Tramadol is rapidly distributed in the body; plasma protein binding is about 20%. Tramadol is mainly metabolised by O- and N-demethylation and by conjugation reactions forming glucuronides and sulfates. Tramadol and its metabolites are mainly excreted via the kidneys. The mean elimination half-life is about 6 hours. The O-demethylation of tramadol to M1, the main analgesic effective metabolite, is catalysed by cytochrome P450 (CYP) 2D6, whereas N-demethylation to M2 is catalysed by CYP2B6 and CYP3A4. The wide variability in the pharmacokinetic properties of tramadol can partly be ascribed to CYP polymorphism. O- and N-demethylation of tramadol as well as renal elimination are stereoselective. Pharmacokinetic-pharmacodynamic characterisation of tramadol is difficult because of differences between tramadol concentrations in plasma and at the site of action, and because of pharmacodynamic interactions between the two enantiomers of tramadol and its active metabolites. The analgesic potency of tramadol is about 10% of that of morphine following parenteral administration. Tramadol provides postoperative pain relief comparable with that of pethidine, and the analgesic efficacy of tramadol can further be improved by combination with a non-opioid analgesic. Tramadol may prove particularly useful in patients with a risk of poor cardiopulmonary function, after surgery of the thorax or upper abdomen and when non-opioid analgesics are contraindicated. Tramadol is an effective and well tolerated agent to reduce pain resulting from trauma, renal or biliary colic and labour, and also for the management of chronic pain of malignant or nonmalignant origin, particularly neuropathic pain. Tramadol appears to produce less constipation and dependence than equianalgesic doses of strong opioids.

Intramuscular tramadol increases gastric pH during anesthesia

PURPOSE

Tramadol, [(1RS, 2RS)-2-dimethylamino) methyl-1-(3-methoxyphenyl)-cyclohexanol hydrochloride], is an analgesic in clinical use. It has been reported that tramadol inhibits muscarinic type 3 receptor function, which primarily mediates smooth muscle contraction and glandular secretion. We investigated the effects of tramadol on the pH of gastric juices during anesthesia to determine whether tramadol inhibits secretion from the gastric glands.

METHODS

ASA physical status I or II adult patients (n = 30) presenting for major elective orthopedic surgery of the upper extremities or mastectomy were enrolled. Patients were randomly assigned to receive treatment with tramadol (n = 10), famotidine (n = 10), or saline (n = 10). General anesthesia was then induced using propofol, vecuronium bromide, and fentanyl. After inducing anesthesia, the gastric pH was measured using pH test paper and, then, 100 mg tramadol, 20 mg famotidine, or saline were injected into the deltoid muscle. Three hours after starting the operation, gastric juice was again aspirated and its gastric pH measured.

RESULTS

There were no differences in the pH before anesthesia between the three groups. By contrast, gastric pH was increased in the tramadol group by the same amount as it was in the famotidine group three hours after administering the drugs. Gastric pH of the saline, famotidine, and tramadol groups was 2.6 +/- 2.5, 6.3 +/- 2.0, and 6.4 +/- 0.8, respectively.

CONCLUSION

These results suggest that tramadol inhibits the secretion of gastric acid.

Opioids and the gut: pharmacology and current clinical experience

This article reviews the pharmacology and physiology of opiate receptors and the current and potential uses of opioid agonists and antagonists in clinical gastroenterology. Mu-receptors are involved in motor and sensory functions, and their modulation is established for treatment of diarrhea. Mu-antagonists have potential to reverse endogenous (e.g., postoperative ileus) or iatrogenic dysmotility (e.g., opioid bowel dysfunction). Modulation of the function of kappa-receptors may be a novel approach to control visceral pain in functional gut disorders. Results of formal testing of novel opioid modulators are keenly awaited.

Epidural analgesia in gastrointestinal surgery

BACKGROUND

The ideal perioperative analgesia should provide effective pain relief, avoid the detrimental effects of the stress response, be simple to administer without the need for intensive monitoring, and have a low risk of complications.

METHODS

This review defines the physiological effects of epidural analgesia and assesses whether the available evidence supports its preferential use in gastrointestinal surgery. All papers studied were identified from a Medline search or selected by cross-referencing.

RESULTS

Epidural analgesia is associated with a shorter duration of postoperative ileus, attenuation of the stress response, fewer pulmonary complications, and improved postoperative pain control and recovery. It does not reduce anastomotic leakage, intraoperative blood loss, transfusion requirement, risk of thromboembolism or cardiac morbidity, or hospital stay compared with that after conventional analgesia in unselected patients undergoing gastrointestinal surgery. Thoracic epidural analgesia reduces hospital costs and stay in patients at high risk of cardiac or pulmonary complications.

CONCLUSIONS

Epidural analgesia enhances recovery after gastrointestinal surgery. The results support the development of structured regimens of early postoperative feeding and mobilization to exploit the potential for thoracic epidural analgesia to reduce hospital stay after gastrointestinal surgery.

A comparison of preoperative tramadol and morphine for the control of early postoperative pain in canine ovariohysterectomy

OBJECTIVE

To compare morphine with tramadol for the management of early postoperative pain following ovariohysterectomy after pyometra in dogs.

STUDY DESIGN

Prospective randomized blinded clinical trial.

ANIMALS

Thirty female dogs, 2-14 years old.

METHODS

Animals were randomly divided into two equal groups. Group 1 received 0.2 mg kg-1 of morphine IV and group 2 received 2 mg kg-1 of tramadol IV after the induction of anesthesia. The dogs were premedicated with acepromazine, and anesthesia was induced with intravenous midazolam and ketamine. Isoflurane was used for the maintenance of anesthesia. The variables measured were: analgesia; sedation; cardiac and respiratory rates; arterial blood pressure; end-tidal isoflurane and carbon dioxide (Pe'CO2); oxyhemoglobin saturation (SpO2); plasma catecholamines; serum cortisol and glucose concentrations; pH and blood gases. The animals were monitored for 6 hours after the administration of the analgesic agent.

RESULTS

There were no differences between the two groups with regard to analgesia, sedation, SpO2, pH and blood gases, cardiovascular variables, glucose, catecholamine and cortisol concentrations. Forty minutes postopioid administration, the end-tidal isoflurane concentration was significantly lower in the morphine-treated group as compared to the tramadol group. At 30 minutes following opioid injection, Pe'CO2 was significantly higher in the morphine group than in the tramadol group. Two dogs in the tramadol group and one in the morphine group were given morphine postoperatively because of increasing pain scores.

CONCLUSION AND CLINICAL RELEVANCE

Morphine and tramadol, administered preemptively can be used safely in dogs to control early pain after ovariohysterectomy without significant adverse effects.

Impact of CYP2D6 genotype on postoperative tramadol analgesia

Genetic polymorphisms result in absent enzyme activity of CYP2D6 (poor metabolizers, PM) in about 10% of the Caucasian population. This study investigates whether the PM genotype has an impact on the response to tramadol analgesia in postoperative patients. A prospective study design was used and 300 patients recovering from abdominal surgery were enrolled. After titration of an individual loading dose, patients could self-administer 1 ml bolus doses of the drug combination tramadol 20 mg/ml, dipyrone 200 mg/ml and metoclopramide 0.4 mg/ml via patient-controlled analgesia (PCA). Patients' genotype was analyzed considering the most prevalent PM associated CYP2D6 mutations using a real-time PCR and hybridization based genotyping method. Demographic data, surgery related variables, pain scores, analgesic consumption and need for rescue medication were compared between extensive metabolizers (EM) and PM. The primary outcome criterion 'response' was defined as responder or non-responder status by the need for rescue medication and patients' satisfaction at the final interview. Demographic and surgery related data were comparable between EM (n=241) and PM (n=30). The percentage of non-responders was significantly higher in the PM group (46.7%) compared with the EM group (21.6%; p=0.005). Tramadol loading dose amounted to 108.2+/-56.9 and 144.7+/-22.6 mg (p<0.001) in EM and PM, respectively. More patients displaying the PM genotype needed rescue medication in the recovery room and during PCA period than patients with at least one wild type allele (21.6 versus 43.3%, p=0.02). PM for CYP2D6 showed a lower response rate to postoperative tramadol analgesia than EM. Therefore, CYP2D6 genotype has an impact on analgesia with tramadol. Pharmacogenetics may explain some of the varying response to pain medication in postoperative patients.

Postoperative sensitization and pain after cesarean delivery and the effects of single im doses of tramadol and diclofenac alone and in combination

Combining different analgesic mechanisms can reduce postoperative pain. We investigated postoperative pain and sensory sensitization in a double-blinded, placebo-controlled, randomized, single-dose comparison of the monoaminergic and micro -opioid agonist tramadol, 100 mg, and diclofenac 75 mg given IM in combination or alone in 120 patients who had elective cesarean delivery. The time to first postoperative demand for rescue analgesia, pain, tramadol pharmacokinetics, and electrical sensory thresholds at or distant from the incision were studied. The median time to first rescue (interquartile range) was 197 min (70-1000 min) with tramadol plus diclofenac, 48 min (25-90 min) with tramadol plus placebo, 113 min (35-270 min) with diclofenac plus placebo, and 55 min (30-100 min) with double placebo (tramadol plus diclofenac versus all other groups, P < 0.05). Pain intensity decreased markedly over time in all groups, and time and drug effects were significant (analysis of variance; P < 0.00001). Side effects were similarly minimal with all treatments. Pain thresholds at or distant from the incision increased significantly after surgery only with tramadol plus diclofenac. Preoperative sensory thresholds correlated with postoperative sensory changes (r > 0.53; P < 0.0001). The pharmacokinetics of tramadol and O-desmethyltramadol were unchanged by diclofenac. The combination of tramadol and diclofenac resulted in improved analgesia compared with monotherapy. Only the analgesic combination prevented both primary and secondary hyperalgesia. Preoperative sensory thresholds may allow prediction of postoperative sensitization.

IMPLICATIONS

The parenteral combination of tramadol and diclofenac resulted in more prolonged and pronounced postoperative analgesia and reduced sensory sensitization compared with the single drugs, with no increase in side effects.

The addition of a tramadol infusion to morphine patient-controlled analgesia after abdominal surgery: a double-blinded, placebo-controlled randomized trial

In this double-blinded, randomized controlled trial, we tested whether the addition of tramadol to morphine for patient-controlled analgesia (PCA) resulted in improved analgesia efficacy and smaller morphine requirements compared with morphine PCA alone after abdominal surgery in adults. Sixty-nine patients were randomly allocated into two groups, each receiving morphine 1 mg/mL via PCA after surgery. The tramadol group received an intraoperative initial loading dose of tramadol (1 mg/kg) and a postoperative infusion of tramadol at 0.2 mg. kg(-1). h(-1). The control group received an intraoperative equivalent volume of normal saline and a postoperative saline infusion. Postoperatively, tramadol was associated with improved subjective analgesic efficacy (P = 0.031) and there was significantly less PCA morphine use in the tramadol group (P = 0.023). No differences between the groups were found with regard to nausea, antiemetic use, sedation, or quality of recovery (all P > 0.05). We conclude that a tramadol infusion combined with PCA morphine improves analgesia and reduces morphine requirements after abdominal surgery compared with morphine PCA alone.

IMPLICATIONS

In this study, we determined whether adding a second pain-killing drug, tramadol, could improve pain relief after major surgery in patients receiving morphine patient-controlled analgesia. We found that patients receiving tramadol had significantly better opinions of their pain relief and used significantly less morphine with no increase in side effects.

Wound sensitivity as a measure of analgesic effects following surgery in human neonates and infants

Postoperative wound sensitivity following abdominal surgery in neonates and infants has been little investigated, and is not well understood. Our aim was to quantify this sensitivity using the abdominal skin reflex (ASR), and to test the hypothesis that the threshold of this reflex would decrease following surgery, and would increase with the administration of analgesia. We measured ASR thresholds in infants under 1 year receiving unilateral abdominal surgery and in a small comparison group of non-surgical infants. The reflex was elicited by applying calibrated von Frey hairs to both sides of the abdomen at the same segmental level. In addition to threshold, the degree of reflex radiation as denoted by hip flexion was measured. The reflex threshold was significantly lowered at the wound site by up to 78% following surgery, and subsequently increased to varying degrees based on the type of analgesia used. The post-surgical drop in threshold was accompanied by an increase in reflex radiation. Thresholds remained below pre-operative values 24 h after surgery on the operated side. In addition, it was observed that infants in whom the indication for surgery was a chronic condition, displayed lower threshold values on the affected side prior to surgery. An objective and quantitative measure has been developed of wound sensitivity and level of analgesia in infants following surgery. The reflex threshold also provides a means of quantifying human central sensory processing, and may be used to detect referred visceral hypersensitivity in this age group.

An evaluation of the efficacy and tolerability of oral tramadol hydrochloride tablets for the treatment of postsurgical pain in children

In this double-blinded, randomized, multicenter study, we examined analgesic efficacy and tolerability of tramadol in postoperative pediatric patients. Eighty-one postsurgical ASA physical status I and II patients ages 7-16 yr received oral tramadol (approximately 1 or 2 mg/kg) for postoperative analgesia when they were ready to transition from morphine patient-controlled analgesia to oral analgesics. Rescue analgesia consisted of morphine patient-controlled analgesia or an oral equivalent dose of oxycodone. Patients rated their pain just before the administration of tramadol and at regular intervals for 8 h afterwards using the Wong-Baker Faces Pain Rating Scale. The 2-mg/kg group required approximately half as much rescue analgesia as the 1-mg/kg group (P = 0.006). Parents rated the larger dose more favorably. Adverse events were generally mild to moderate in severity (vomiting [10%], nausea [9%], pruritus [7%], rash [4%]) and similar between the two treatment groups. There were no significant changes in hemodynamic variables, respiratory rate, or SpO(2) percentages between the two treatment groups or in all patients compared with pretreatment values.

IMPLICATIONS

Oral tramadol 1-2 mg/kg is well tolerated and effective in postoperative children ready to transition from morphine patient-controlled analgesia. The group receiving 2 mg/kg required less rescue analgesic compared with those receiving 1 mg/kg.

Effects of tramadol on behavioural indicators of colic pain in a rat model of ureteral calculosis

This study investigated the effect of prolonged administration of tramadol vs. placebo on behavioural indicators of ureteral pain and referred lumbar muscle hyperalgesia in a rat model of artificial ureteral calculosis. Four groups of 10 rats each (female, Sprague-Dawley) were treated twice a day, for 4 days, with i.p. injections of tramadol 1.25 mg/kg, 2.5 mg/kg, 5 mg/kg or saline, respectively. The first injection was delivered 45 min before laparotomy (under pentobarbital anaesthesia) for formation of the stone in the upper left ureter via injection of dental cement. All rats were video-taped 24 h non-stop from the immediate postoperative period until the 4th day for recording of behavioural ureteral crises indicative of colic pain. Lumbar muscle sensitivity was tested daily over the same period by verifying presence or absence of vocalization upon pinching of the parietal layers at L1 level, bilaterally, at a constant predefined pressure value with calibrated forceps. Tramadol significantly reduced number and global duration (ANOVA, P < 0.008 and P < 0.004) of ureteral crises with respect to saline and the effect was dose-dependent (linear regression analysis between doses and parameters of crises, P < 0.003 and P < 0.002). The drug also significantly reduced the incidence of referred muscle hyperalgesia (ANOVA, P < 0.0001). It is concluded that tramadol is highly effective in controlling pain phenomena from urinary stones and can represent a valid therapeutic approach in patients with urinary colics.

Changes in sensory processing after surgical nociception

Nociception results in peripheral and central changes in sensory processing. These changes are considered to significantly contribute to postoperative pain and its outcome. Objective measures of changes in sensory processing are now being studied in humans after surgery. Surgical nociception leads to both central excitation (eg, spinal sensitization) and central inhibition (eg, descending inhibition), with inhibition being the dominant response during the first day or so after surgery. Analgesia commenced before surgery (preemptive analgesia) depresses central sensitization and enhances central inhibition. Patients operated on under nonanalgesic anesthesia may exhibit rebound central sensitization for up to 5 days postoperatively after the cessation of postoperative opioid analgesia. There is only a weak relationship between the described objective changes in sensory processing after surgical nociception and subjective clinical pain measures such as pain intensity scales or postoperative analgesic consumption.