Local analgesic efficacy of tramadol following intraplantar injection

Clinical and Antinociceptive Effects of Distal Inferior Alveolar Nerve Block in Ponies With Tramadol 5% or Lidocaine 2

This study aimed to compare the antinociceptive effects of tramadol 5% and lidocaine 2% on mental nerve block in horses of the Brazilian Pony breed. Eight adult non-pregnant mares were used in this study. The ponies were tranquilized with acepromazine (5 µg kg^-1, IV), and the infiltration of the mental foramen was performed in Treatment 1- tramadol 5% (T, 150 mg) or Treatment 2- lidocaine 2% (L, 60 mg), both at a total dose of 3 ml in each foramen. Heart rate (HR), respiratory rate (RR), systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP), rectal temperature (RT), and formation of skin lesions (SL) were evaluated. Evaluation of nociception of the outer lip (OL), inner lip (IL), and gingiva (GG) were performed using an electronic von Frey device with the evaluation of the ponies' reactions to each stimulus. From these reactions, we determined latency time (LT) and duration of antinociception (DAN). Analysis of variance with 16 observations was performed for HR, RR, SAP, DAP, MAP, LT and DAN. Data were expressed as mean ± standard deviation and the means were compared by the SNK and Student's t-test (P< 0.05). Changes in HR, RR, SAP, DAP, and MAP between evaluation times were associated with the effects of acepromazine (P>0.05). No formation of skin lesions was observed. Latency time did not differ between treatments (P>0.05). Both lidocaine 2% and tramadol 5% produced an antinociceptive effect. We conclude that the duration of the antinociceptive effect of tramadol 5% is longer than that of lidocaine 2%.

Anti-inflammatory potential of liraglutide, a glucagon-like peptide-1 receptor agonist, in rats with peripheral acute inflammation

The present study aimed to explore the possible anti-inflammatory actions of liraglutide (LRG), a glucagon-like peptide-1 (GLP-1) receptor agonist, and to compare with tramadol (TR) or LRG, and TR combination treatment by investigating the inflammatory signs such as pain hypersensitivity, edema, and fever in carrageenan (CG)-induced acute peripheral inflammation model in rats. The levels of several biomarkers for inflammatory status, angiogenesis, and oxidative stress were also measured in inflamed tissues. CG induced inflammation in the paws of rats identified by hypersensitivities, redness, edema and fever. LRG, significantly improved the hypersensitivity to mechanical (from 4 to 35.5 g) or cold (from 5 to 44.2 s) stimuli, reduced the edema (paw mass, from 2.54 to 1.85 g), and fever (paw temperature, from 33.6 to 27.3 °C). LRG dramatically suppressed the inflammatory signs when compared to those of TR. In addition, co-administration of TR and LRG resulted in further reduction of sensitivity to mechanical and cold stimuli. Anti-inflammatory potential of LRG altered depending on their inhibitory effects in the biomarkers of inflamed paws. Consequently, the suppressive actions of LRG in the inflammation induced hypersensitivities, edema, and fever, indicating that these drugs have significant anti-inflammatory potential with anti-hypersensitivities, anti-edema, and anti-pyretic effects. LRG with anti-inflammatory actions may be a highly promising therapeutic option for the management of inflammatory conditions or inflammatory-related various diseases.

Evaluation of the paw withdrawal latency for the comparison between tramadol and butorphanol administered locally, in the plantar surface of rat, preliminary study

The aim of the study was to evaluate the analgesic efficacy of tramadol compared to butorphanol administered locally in ventral surface of the hind paw of rats. Prospective, randomized experimental study; twenty-one adult male Wistar rats were selected. Heart rate (beats minute^-1), respiratory rate (breaths minute^-1), and paw withdrawal latency (onset of radiant heat until paw withdrawal/seconds) were measured prior (T⁰) and after (T⁵, T¹⁰, T¹⁵, T²⁰) intraplantar injection with saline solution 0,9% (group S), butorphanol 1 mg kg^-1 (group B), and tramadol 1 mg kg^-1 (group T). Shapiro-Wilk normality test and Friedman test were used to analyze the data expressed by median and range. Statistical significance was set at p < 0.05. Statistical analysis of heart rate showed that there were significant differences between groups at different monitoring times. There were no significant differences in respiratory rate after intraplantar injection in any of the treatment groups. The paw withdrawal latency values at T5, T10, and T15 minutes after intraplantar injection in the group B were significantly higher compared to baseline value and to the values of the other groups. The paw withdrawal latency were no significant changes in the measurements of intragroup in S and T. Intraplantar administration of butorphanol provides a good analgesia and significantly increases paw withdrawal latency compared to tramadol. Intraplantar injection of butorphanol could be useful and safe and safe technique to achieve local analgesia for minor surgical procedures in rats.

Antinociception and less gastric injury with the dexketoprofen-tapentadol combination in mice

The purpose of this study was to evaluate the antinociceptive interaction between dexketoprofen and tapentadol in three different dose ratios, as well as the ulcerogenic activity of this combination. Dose-response curves were carried out for dexketoprofen, tapentadol, and dexketoprofen-tapentadol combinations in the acetic acid-induced writhing test in mice. On the other hand, the gastric damage of all treatments was assessed after the surgical extraction of the stomachs. Intraperitoneal administration of dexketoprofen and tapentadol induced a dose-dependent antinociceptive effect, reaching a maximal effect of about 58% and 99%, respectively. Isobolographic analysis and the interaction index showed that the three proportions produced an analgesic potentiation (synergistic interaction). Interestingly, the 1:1 and 1:3 ratios of the drugs combination produced minor gastric injury in comparison with the 3:1 proportion. Our data suggest that all proportions of the dexketoprofen-tapentadol combination produced a synergistic interaction in the acetic acid-induced visceral pain model in mice with a low incidence of gastric injury.

Analgesic Efficacy and Safety of Local Infiltration of Tramadol in Pediatric Tonsillectomy Pain: A Systematic Review and Meta-Analysis

OBJECTIVES

The aim of this systematic review and meta-analysis was to appraise clinical evidence of the impact of peritonsillar infiltration of tramadol, on postoperative pain control and the occurrence of adverse effects in children undergoing tonsillectomy.

METHODS

A database search was conducted to identify randomized controlled trials (RCTs) pertinent to peritonsillar infiltration of tramadol compared to no treatment (placebo) or other analgesic regimens. The outcomes of interest were postoperative pain intensity, time to first analgesic demand, rescue analgesic consumption up to 24 hours after intervention, and the occurrence of adverse events.

RESULTS

Twelve RCTs enrolling 972 pediatric patients were selected for qualitative analysis, among which eight were suitable for meta-analysis. Tramadol infiltration induced a significant reduction of pain intensity up to 24 hours post-tonsillectomy (mean difference [MD], -2.31; 95% confidence interval [CI], -3.49 to -1.12; P < 0.001; I²  = 97%) and time to first analgesic (MD 180.54; 95% CI, 56.91 to 304.18; P = 0.004; I²  = 99%), with no profound impact on postoperative nausea and vomiting (risk ratio [RR] 0.98; 95% CI, 0.73 to 1.32; P = 0.90; I²  = 0%) compared to the placebo group. The analgesic efficacy of tramadol infiltration was equivalent to the local or systematic use of ketamine or infiltration with local anesthetics. This effect was further enhanced when tramadol infiltration served as an adjunct to other analgesic interventions. No serious adverse events were reported.

CONCLUSIONS

In children undergoing tonsillectomy, peritonsillar infiltration of tramadol is associated with a postoperative analgesic benefit when compared to placebo, with negligible adverse events. Yet, no definite conclusion can be drawn due to the low quality, considerable heterogeneity, and paucity of the available data.

Microneedles Coated with Tramadol Exhibit Antinociceptive Effect in a Rat Model of Temporomandibular Hypernociception

Coated microneedles have emerged as a promising drug delivery system for inflammatory pain treatment. We have previously shown that tramadol injection into the rat temporomandibular joint (TMJ) induces an antinociceptive and anti-inflammatory effect. In this study, microneedles coated with tramadol were investigated as a platform to treat TMJ pain. Male Wistar rats were administered tramadol using an intra-TMJ injection or with microneedles coated with tramadol, followed by 1.5% formalin nociceptive challenge administered 15 minutes later. The nociceptive behavior of rats was evaluated, and their periarticular tissues were removed after euthanasia for analysis. The duration of antinociceptive effect was determined by performing the formalin challenge at different time points extending up to 6 days post tramadol administration. Microneedles coated with tramadol produced an antinociceptive effect similar to injection of tramadol into the rat TMJ. Surprisingly, tramadol delivery using coated microneedles produced a more durable antinociceptive effect lasting as much as 2 days post tramadol delivery as compared with an antinociceptive effect lasting under 2 hours from intra-TMJ injection of tramadol. The proinflammatory cytokines tumor necrosis factor-α and interleukin-1β (IL-1β) were found to be reduced, whereas the anti-inflammatory cytokine IL-10 was found to be elevated in tramadol-treated groups. In conclusion, microneedles coated with tramadol can offer a therapeutic option for pain control of inflammatory disorders in the TMJ.

The effect of lidocaine and tramadol in nasal packs on pain after septoplasty

PURPOSE

The aim of this study is to compare the analgesic effects of tramadol-absorbed merocel nasal packings and lidocaine-absorbed merocel nasal packings using visual analog scale (VAS) in the postoperative period in patients undergoing septoplasty operation.

MATERIALS AND METHODS

Our study was applied as a retrospective. Informations about the patients were accessed via their medical records. Our study was performed on 122 patients aged between 18 and 50 years. Patients were divided into three groups according to the application of lidocaine, tramadol and 0.9% NaCl on merocel nasal packings. In the postoperative period, VAS (visual analog scale) scores, side effects, additional analgesic requirements were recorded for 24 h starting from PACU (post anesthetic care unit).

RESULTS

There was no difference between the number of male and female patients (p > 0.05). Postoperative pain was evaluated with VAS score periodically in postoperative 5 min-24 h in all groups. When we compared the groups with each other, there was a statistically significant difference between the tramadol-lidocaine and tramadol-control group (p < 0.05).

CONCLUSION

Tramadol infiltrated to nasal packings decrease the need of additional analgesics in the postoperative period, increases patients' satisfaction, decreases the length of hospital stay, and as a result, reduced the rate of secondary infections.

Tramadol hydrochloride: An alternative to conventional local anaesthetics for intraoral procedures- a preliminary study

Purpose

To evaluate and compare the soft tissue anaesthesia produced by tramadol hydrochloride on gingival tissues in maxilla.

Methods

A total of 50 ASA physical status I subjects between 18 and 35 years of age, both male and female were included in the study. Each individual received 0.5 ml of 50 mg tramadol in the soft tissues over maxillary canine tooth as local infiltration on one and 0.5 ml of 20 mg lignocaine on the contralateral side in a double-blinded fashion. After completing the injection, the author recorded pain on injection, the onset of action, duration of anaesthesia, side effects, and feedback from patient.

Results

The mean onset of anaesthesia for tramadol was 172.00 s (standard deviation 39.898) while for lignocaine it was 162.60 s (standard deviation 35.098) and there was no statistically significant difference between the two groups (p = 0.214). The mean duration of anaesthesia for tramadol group was 45.70 min with a standard deviation of 8.512 min whereas for lignocaine group it was 44.70 min with a standard deviation of 8.107 min. There was no statistical relevant difference between the two groups in duration of anaesthesia (p = 0.549). None of the subjects reported any side effect in both the groups. There was no significant difference in pain on injection between the two groups.

Conclusions

Tramadol has a local anaesthetic effect similar to lignocaine when injected as infiltration in oral soft tissues.

Comparison of Local Anaesthetic Efficacy of Tramadol Versus Lignocaine for Extraction of Tooth Under Supraperiosteal Infiltration

Background

Tramadol has been shown to have a local anaesthetic effect when used as infiltration anaesthesia.

Methods

The local anaesthetic efficacy of tramadol was compared with that of lignocaine for the extraction of teeth in terms of their onset of action, duration of action, intraoperative pain, post-operative analgesic effect and adverse reactions. Apart from this, incidence of allergic reaction was also recorded for both the drugs. A total of 100 patients were divided into two groups randomly. Each patient was assigned to receive either a maximum of 2 ml of 5% tramadol (Supridol 50 mg, Neon laboratories), Group T (n = 50), as a local anaesthetic solution for extraction of maxillary premolar for orthodontic reason under supraperiosteal infiltration following strict aseptic precaution or a maximum of 2 ml of 2% lignocaine (Lox 2%, Neon laboratories), Group L (n = 50), in a double-blinded fashion.

Results

In group T, the mean subjective onset of action was 33.66 s, while in group L it was 33.06 s (p = 0.881). In group T, the mean objective onset of action was 3.04 min, while in group L it was 3.18 min (p > 0.05). The mean duration of action in group T was 55.60 min, while in group L it was 57.50 min (p = 0.432). Only 2 patients in group T and 1 patient in group L had nausea (p = 0.245).

Conclusion

We conclude that 5% tramadol has a local anaesthetic efficacy similar to 2% lignocaine but is comparatively a weaker agent.

The anti-inflammatory effect of tramadol in the temporomandibular joint of rats

Tramadol is a centrally acting analgesic drug able to prevent nociceptor sensitization when administered into the temporomandibular joint (TMJ) of rats. The mechanism underlying the peripheral anti-inflammatory effect of tramadol remains unknown. This study demonstrated that intra-TMJ injection of tramadol (500µg/TMJ) was able to inhibit the nociceptive response induced by 1.5% formalin or 1.5% capsaicin, suggesting that tramadol has an antinociceptive effect, acting directly on the primary nociceptive neurons activating the nitric oxide/cyclic guanosine monophosphate signaling pathway. Tramadol also inhibited the nociceptive response induced by carrageenan (100µg/TMJ) or 5-hydroxytryptamine (225µg/TMJ) along with inhibition of inflammatory cytokines levels, leukocytes migration and plasma extravasation. In conclusion, the results demonstrate that peripheral administration of tramadol has a potential antinociceptive and anti-inflammatory effect. The antinociceptive effect is mediated by activation of the intracellular nitric oxide/cyclic guanosine monophosphate pathway, at least in part, independently from the opioid system.

PRESSÃO INTRAOCULAR, PRESSÃO ARTERIAL MÉDIA E DIÂMETRO PUPILAR EM COELHOS ( (Oryctolagus cuniculus) ) SUBMETIDOS AO BLOQUEIO RETROBULBAR COM DIFERENTES PROTOCOLOS ANESTÉSICOS

Resumo O objetivo deste estudo foi buscar novos protocolos de anestesia loco regional para procedimentos oftálmicos que proporcionem segurança e manutenção das funções vitais, além de manter a pressão intraocular estável, com centralização do bulbo do olho e acinesia palpebral. Foram utilizados 20 coelhos da raça Nova Zelândia para a realização de quatro protocolos de anestesia local através do bloqueio retrobulbar com lidocaína 2% com vasoconstritor, lidocaína 2% sem vasoconstritor associada ao tramadol, ropivacaína 1% e bupivacaína 0,5%, cada animal recebeu o volume anestésico de 1,0 mL. Todos os protocolos anestésicos utilizados promoveram acinesia palpebral e centralização do bulbo do olho durante todo o período de avaliação. A realização do bloqueio retrobulbar com os protocolos anestésicos demonstrou ser factível e segura quanto à manutenção da pressão intraocular, pressão arterial invasiva e diâmetro pupilar e pode ser utilizada para realização de cirurgias intraoculares. Os anestésicos proporcionaram bom bloqueio retrobulbar, entretanto a bupivacaína foi o anestésico que ocasionou o maior diâmetro pupilar comparativamente aos demais fármacos testados.

Local analgesic effect of tramadol is not mediated by opioid receptors in early postoperative pain in rats

BACKGROUND AND OBJECTIVES

Tramadol is known as a central acting analgesic drug, used for the treatment of moderate to severe pain. Local analgesic effect has been demonstrated, in part due to local anesthetic-like effect, but other mechanisms remain unclear. The role of peripheral opioid receptors in the local analgesic effect is not known. In this study, we examined role of peripheral opioid receptors in the local analgesic effect of tramadol in the plantar incision model.

METHODS

Young male Wistar rats were divided into seven groups: control, intraplantar tramadol, intravenous tramadol, intravenous naloxone-intraplantar tramadol, intraplantar naloxone-intraplantar tramadol, intravenous naloxone-intravenous tramadol, and intravenous naloxone. After receiving the assigned drugs (tramadol 5mg, naloxone 200 μg or 0.9% NaCl), rats were submitted to plantar incision, and withdrawal thresholds after mechanical stimuli with von Frey filaments were assessed at baseline, 10, 15, 30, 45 and 60 min after incision.

RESULTS

Plantar incision led to marked mechanical hyperalgesia during the whole period of observation in the control group, no mechanical hyperalgesia were observed in intraplantar tramadol group, intraplantar naloxone-intraplantar tramadol group and intravenous naloxone-intraplantar tramadol. In the intravenous tramadol group a late increase in withdrawal thresholds (after 45 min) was observed, the intravenous naloxone-intravenous tramadol group and intravenous naloxone remained hyperalgesic during the whole period.

CONCLUSIONS

Tramadol presented an early local analgesic effect decreasing mechanical hyperalgesia induced by plantar incision. This analgesic effect was not mediated by peripheral opioid receptors.

Does tramadol affect coagulation status of patients with malignancy?

AIM

The study investigated the direct effects of tramadol on the coagulation status of women with gynecologic malignancies in vitro.

MATERIALS AND METHODS

Citrated whole-blood samples from 21 patients with gynecologic tumors were spiked ex vivo with 2 or 6 μl/ml tramadol. Thrombelastography (TEG) analysis was performed using ROTEM(®) to assess clotting time (CT), clot formation time (CFT) and maximum clot formation (MCF).

RESULTS

In the INTEM assay, CT (P < 0.05) and CFT (P < 0.01) were significantly prolonged with tramadol at a 6 μl/ml concentration compared with baseline. There were no significant differences in MCF values between the baseline and the tramadol-treated samples (P > 0.05). Blood medicated with tramadol (6 μl/ml) clotted slowly (increased CT and CFT).

CONCLUSION

The changes observed by TEG demonstrated that tramadol impairs hemostasis in a concentration-dependent manner in the whole blood of women with gynecologic malignancies in vitro.

[Local analgesic effect of tramadol is not mediated by opioid receptors in early postoperative pain in rats]

BACKGROUND AND OBJECTIVES

Tramadol is known as a central acting analgesic drug, used for the treatment of moderate to severe pain. Local analgesic effect has been demonstrated, in part due to local anesthetic-like effect, but other mechanisms remain unclear. The role of peripheral opioid receptors in the local analgesic effect is not known. In this study, we examined role of peripheral opioid receptors in the local analgesic effect of tramadol in the plantar incision model.

METHODS

Young male Wistar rats were divided into seven groups: control, intraplantar tramadol, intravenous tramadol, intravenous naloxone-intraplantar tramadol, intraplantar naloxone-intraplantar tramadol, intravenous naloxone-intravenous tramadol, and intravenous naloxone. After receiving the assigned drugs (tramadol 5mg, naloxone 200μg or 0.9% NaCl), rats were submitted to plantar incision, and withdrawal thresholds after mechanical stimuli with von Frey filaments were assessed at baseline, 10, 15, 30, 45 and 60min after incision.

RESULTS

Plantar incision led to marked mechanical hyperalgesia during the whole period of observation in the control group, no mechanical hyperalgesia were observed in intraplantar tramadol group, intraplantar naloxone-intraplantar tramadol group and intravenous naloxone-intraplantar tramadol. In the intravenous tramadol group a late increase in withdrawal thresholds (after 45min) was observed, the intravenous naloxone-intravenous tramadol group and intravenous naloxone remained hyperalgesic during the whole period.

CONCLUSIONS

Tramadol presented an early local analgesic effect decreasing mechanical hyperalgesia induced by plantar incision. This analgesic effect was not mediated by peripheral opioid receptors.

Spinal and peripheral adenosine A₁ receptors contribute to antinociception by tramadol in the formalin test in mice

Tramadol, an analgesic used alone or combined with acetaminophen, has a complex mechanism of action involving opioid and amine mechanisms. In this study, we explored the involvement of spinal and peripheral adenosine A1 receptors in antinociception by tramadol, and determined whether spinal serotonin 5-HT₇ receptors were linked to spinal A1 receptor actions. Antinociception was examined using the 2% formalin test in mice. Tramadol was administered systemically (intraperitoneal) or peripherally (intraplantar). Caffeine (non-selective A₁/A₂A receptor antagonist) and SCH58261 (selective A₂A receptor antagonist) were given systemically, while DPCPX (selective A₁ receptor antagonist) was given systemically, spinally (lumbar puncture), or peripherally. Systemic tramadol 35 mg/kg produced antinociception against phase 2 formalin-evoked flinching behaviors, particularly in the earlier parts (phase 2A). Systemic caffeine (10 mg/kg) and DPCPX (1 mg/kg), but not SCH58261 (3 mg/kg), inhibited antinociception by systemic tramadol. Spinal DPCPX 3 μg also inhibited the action of systemic tramadol. Spinal SB269970 (selective 5-HT₇ receptor antagonist) 3-10 μg did not alter the effect of systemic tramadol. Intraplantar tramadol produced antinociception against flinching behaviors, and this action was reversed by intraplantar DPCPX 4.5 μg administered on the ipsilateral, but not contralateral, side. Intraplantar DPCPX also reversed antinociception by systemic tramadol. These results indicate that adenosine A₁ receptors contribute to antinociception by tramadol in the mouse formalin model, and that spinal and peripheral sites are involved in these actions. 5HT₇ receptors in the spinal cord do not appear to be involved in the recruitment of A₁ receptor mechanisms when tramadol is given systemically in this model.

The efficacy of submucosal tramadol in the postoperative treatment of pain following septoplasty operations

Tramadol is a centrally acting opioid which is effective for moderate-severe pain and is being used for various acute and chronic pain scenarios. The primary endpoint of this controlled, randomized double blind study was to evaluate the effect of submucosal tramadol on VAS scores after septoplasty operations and secondary endpoint was to investigate the effects on total opioid and additional analgesic consumption and patient satisfaction. 60 patients scheduled for septoplasty under general anaesthesia were enrolled. In Group T, at the end of surgery following hemostasis, 2 mg/kg tramadol was applied as submucosal infiltration to both surgical sites, 2 ml (total 4 ml), by the surgeon. In Group P, at the end of surgery following hemostasis, 2 ml isotonic solution (total 4 ml) was applied as submucosal infiltration to both surgical sites by the surgeon. Total opioid consumption, VAS scores, patient satisfaction was evaluated at the end of 24 h VAS values were higher in Group P on the first and second postoperative hours. Patient controlled analgesia demand and delivery values were higher in Group P on the postoperative 1, 2, 4, 6, 12 and 24th hours. Patient satisfaction was higher and opioid consumption was lower in Group T compared to Group P. There was no difference in additional analgesic consumption between two groups. The results show that patients receiving tramadol had lower VAS scores compared with the placebo groups postoperatively.

Percutaneous sciatic nerve block with tramadol induces analgesia and motor blockade in two animal pain models

Local anesthetic efficacy of tramadol has been reported following intradermal application. Our aim was to investigate the effect of perineural tramadol as the sole analgesic in two pain models. Male Wistar rats (280-380 g; N = 5/group) were used in these experiments. A neurostimulation-guided sciatic nerve block was performed and 2% lidocaine or tramadol (1.25 and 5 mg) was perineurally injected in two different animal pain models. In the flinching behavior test, the number of flinches was evaluated and in the plantar incision model, mechanical and heat thresholds were measured. Motor effects of lidocaine and tramadol were quantified and a motor block score elaborated. Tramadol, 1.25 mg, completely blocked the first and reduced the second phase of the flinching behavior test. In the plantar incision model, tramadol (1.25 mg) increased both paw withdrawal latency in response to radiant heat (8.3 ± 1.1, 12.7 ± 1.8, 8.4 ± 0.8, and 11.1 ± 3.3 s) and mechanical threshold in response to von Frey filaments (459 ± 82.8, 447.5 ± 91.7, 320.1 ± 120, 126.43 ± 92.8 mN) at 5, 15, 30, and 60 min, respectively. Sham block or contralateral sciatic nerve block did not differ from perineural saline injection throughout the study in either model. The effect of tramadol was not antagonized by intraperitoneal naloxone. High dose tramadol (5 mg) blocked motor function as well as 2% lidocaine. In conclusion, tramadol blocks nociception and motor function in vivo similar to local anesthetics.

Comparison of actions of systemically and locally administrated local anaesthetics in diabetic rats with painful neuropathy

Nothing is known about actions of levobupivacaine, a long-acting local anaesthetic belonging to the amino amide group, in diabetes-induced neuropathic pain conditions. In this study, we therefore investigated the possible antihyperalgesic and antiallodynic effects of levobupivacaine in diabetic animal model. Actions of systemically (intraperitoneal) or locally (intraplantar) administrated levobupivacaine on streptozotocin-induced diabetic rats with painful neuropathy were examined using a thermal plantar test and a dynamic plantar aesthesiometer. Effects of levobupivacaine were compared with those of a well-known amide local anaesthetic lidocaine. Levobupivacaine was more potent than lidocaine in all tests employed on diabetic rats. After intraperitoneal injections to diabetic rats, levobupivacaine, but not lidocaine, produced pronounced antihyperalgesic and antiallodynic effects. However, intraplantar administration of both levobupivacaine and lidocaine produced antihyperalgesic and antiallodynic action in diabetic rats. In contrast to the transient effects of lidocaine (30 min), antihyperalgesic and antiallodynic actions of levobupivacaine gradually disappeared within 120 min after intraplantar injections. Intraperitoneal or intraplantar administrations of levobupivacaine or lidocaine at the effective dose had no effect on any parameters in intact rats. Findings revealed that antiallodynic and antihyperalgesic potency of levobupivacaine was higher in comparison with that of lidocaine after their intraperitoneal or intraplantar administration to diabetic animals. Furthermore, locally administrated levobupivacaine has the greatest antihyperalgesic and antiallodynic actions in diabetic rats.

Effects of local tramadol administration on peripheral glutamate-induced nociceptive behaviour in mice

PURPOSE

The use of peripheral tramadol to block pain has been advocated. However, since its actions in the periphery have not been elucidated fully, we tested the hypothesis that peripheral tramadol blocks peripheral glutamate-induced nociceptive behaviour in mice.

METHODS

First, we compared the duration of paw licking after intraplantar (ipl.) glutamate administration, with and without tramadol, using a randomized blinded controlled design. Next, we established the half maximal effective concentrations (EC(50s)) for local tramadol and reference compound lidocaine in the hot water tail-flick latency test and the glutamate-induced paw allodynia assay.

RESULTS

Tramadol reduced glutamate-induced paw licking from 33 +/- 12 sec to 4 +/- 4 sec (mean +/- SD; t test, P < 0.05; n = 6 per group). The tramadol and lidocaine EC(50) nerve conduction blocks in the tail did not differ significantly (84 +/- 24 mM vs 69 +/- 5 mM, respectively). Although tramadol reduced glutamate-induced allodynia (EC(50), 46 +/- 13 mM), lidocaine was more potent (EC(50), 13 +/- 5 mM; Dixon's up-and-down method; P < 0.05). Tramadol was 2.5 times as effective at blocking nerve conduction in the tail compared with allodynia in the paw.

CONCLUSIONS

Local tramadol administration blocked nociceptive behaviour in mice induced by peripheral glutamate. Compared with lidocaine, the relative potency of tramadol was lower for blocking glutamate-induced allodynia than for sensory nerve conduction blockade, suggesting the activation of a pronociceptive receptor system in the periphery.

Macrophage depletion delays progression of neuropathic pain in diabetic animals

Despite the fact that it is a frequent diabetic complication, the mechanisms underlying the manifestation of diabetic neuropathic pain remain poorly understood. In this study, we hypothesized that the depletion of peripheral macrophages with liposome-encapsulated clodronate (LEC) can prevent, at least delay, the progression of diabetes-induced neuropathic pain. Therefore, the aim of this study was to evaluate the effects of macrophage depletion on mechanical allodynia and thermal hyperalgesia in the streptozotocin (STZ)-induced rat model of diabetic neuropathy. LEC was intravenously administrated to rats three times with 5-day intervals. A single intravenous injection of STZ caused an increase in the average blood glucose levels and a decrease in body weight. Although LEC treatment did not affect the body weight gain, the blood glucose level was lower and serum insulin level higher in LEC-treated diabetic rats than in that of diabetic rats. In addition, LEC treatment alleviated the excessive damage in beta cells in diabetic rats. Diabetic animals displayed marked mechanical allodynia and thermal hyperalgesia. While the treatment of diabetic rats with LEC did not significantly change the thermal withdrawal latency, diabetes-induced decrease in mechanical paw withdrawal threshold was significantly corrected by the LEC treatment. The results of this study show that thermal hyperalgesia and mechanical allodynia induced by diabetes may be associated with alterations in blood glucose level. Depletion of macrophages with LEC in diabetic rats may reduce mechanical allodynia without affecting thermal hyperalgesia. Taken together, these results suggested that depletion of macrophages in diabetes may partially postpone the development of diabetic neuropathic pain.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Role of 4-aminopyridine-sensitive potassium channels in peripheral antinociception

Previous studies has report the modulation of K+ channels play key roles in the induction of peripheral antinociception induced by many types of drugs. However, the possible participation of 4-aminopyridine-sensitive K+ channels to local antinociception induced by tramadol, a mu opioid receptor agonist, and lidocaine, a local anaesthetic, has been less studied. In this study, we therefore investigated this by using thermal plantar test. Tramadol or lidocaine administered intraplantarly into the hind paw elicited an antinociceptive effect. 4-aminopyridine caused an increase in the antinociception produced by lidocaine. However, tramadol induced antinociception remained unaffected by intraplantar administration of 4-aminopyridine. These results suggest that 4-aminopyridine-sensitive K+ channels may play an important role in the thermal peripheral antinociception produced by lidocaine, but not tramadol.