Differential effects of lidocaine and tramadol on modified nerve impulse by 4-aminopyridine in rats

Intraoperative and Postoperative Effects of Dexmedetomidine and Tramadol Added as an Adjuvant to Bupivacaine in Transversus Abdominis Plane Block

Background: We aimed to evaluate the intraoperative hemodynamics, opioid consumption, muscle relaxant use, postoperative analgesic effects, and possible adverse effects (such as nausea and vomiting) of dexmedetomidine and tramadol added as adjuvants to bupivacaine in the transversus abdominis plane block (TAP block) to provide postoperative analgesia. Materials and Methods: This was a prospective, randomized, controlled trial on patients who underwent laparoscopic cholecystectomy. After obtaining ethical approval at the Van Yuzuncu Yil University and written informed consent, this investigation was registered with ClinicalTrials.gov (NCT05905757). The study was conducted with 67 patients with ASA I-II physical status, aged 20-60 years, of either sex who were scheduled for an elective laparoscopic cholecystectomy under general anesthesia. Exclusion criteria were the patient's refusal, ASA III and above, a history of allergy to the study drugs, patients with severe systemic diseases, pregnancy, psychiatric illness, seizure disorder, and those who had taken any form of analgesics in the last 24 h. The patients were equally randomized into one of two groups: Group T (TAP Block group) and Group D (Dexmedetomidin group). Standard general anesthesia was administered. After intubation, Group T (Bupivacaine + adjuvant tramadol) = solutions containing 0.250% bupivacaine 15 mL + adjuvant 1.5 mg/kg (100 mg maximum) tramadol 25 mL and Group D (Bupivacaine + adjuvant dexmedetomidine) = solutions containing 0.250% bupivacaine 15 mL + 0.5 mcg/kg and (50 mcg maximum) dexmedetomidine 25 mL; in total, 40 mL and 20 mL was applied to groups T and D, respectively. A bilateral subcostal TAP block was performed by the same anesthesiologist. Intraoperative vital signs, an additional dose of opioid and muscle relaxant requirements, complications, postoperative side effects (nausea, vomiting), postoperative analgesic requirement, mobilization times, and the zero-hour mark (patients with modified Aldrete scores of 9 and above were recorded as 0 h), the third-hour, and sixth-hour visual analog scale (VAS) scores were recorded. The main outcome measurements were the effect on pain scores and analgesic consumption within the first 6 h postoperatively, postoperative nausea and vomiting (PONV), and time to ambulation. The secondary aim was to evaluate intraoperative effects (on hemodynamics and opioid and muscle relaxant consumption). Results: It was observed that dexmedetomidine and tramadol did not have superiority over each other in terms of postoperative analgesia time, analgesic consumption, side effect profile, and mobilization times (p > 0.05). However, more stable hemodynamics were observed with dexmedetomidine as an adjuvant. Conclusions: We think that the use of adjuvant dexmedetomidine in the preoperative TAP block procedure will provide more stable intraoperative hemodynamic results compared with the use of tramadol. We believe that our study will be a guide for new studies conducted with different doses and larger numbers of participants.

The opioid tramadol blocks the cardiac sodium channel Nav1.5 in HEK293 cells

AIMS

Opioids are associated with increased risk of sudden cardiac death. This may be due to their effects on the cardiac sodium channel (Nav1.5) current. In the present study, we aim to establish whether tramadol, fentanyl, or codeine affects Nav1.5 current.

METHODS AND RESULTS

Using whole-cell patch-clamp methodology, we studied the effects of tramadol, fentanyl, and codeine on currents of human Nav1.5 channels stably expressed in HEK293 cells and on action potential (AP) properties of freshly isolated rabbit ventricular cardiomyocytes. In fully available Nav1.5 channels (holding potential -120 mV), tramadol exhibited inhibitory effects on Nav1.5 current in a concentration-dependent manner with an IC50 of 378.5 ± 33.2 µm. In addition, tramadol caused a hyperpolarizing shift of voltage-gated (in)activation and a delay in recovery from inactivation. These blocking effects occurred at lower concentrations in partially inactivated Nav1.5 channels: during partial fast inactivation (close-to-physiological holding potential -90 mV), IC50 of Nav1.5 block was 4.5 ± 1.1 μm, while it was 16 ± 4.8 μm during partial slow inactivation. The tramadol-induced changes on Nav1.5 properties were reflected by a reduction in AP upstroke velocity in a frequency-dependent manner. Fentanyl and codeine had no effect on Nav1.5 current, even when tested at lethal concentrations.

CONCLUSION

Tramadol reduces Nav1.5 currents, in particular, at close-to-physiological membrane potentials. Fentanyl and codeine have no effects on Nav1.5 current.

Tramadol as a Voltage-Gated Sodium Channel Blocker of Peripheral Sodium Channels Nav1.7 and Nav1.5

Tramadol is an opioid analog used to treat chronic and acute pain. Intradermal injections of tramadol at hundreds of millimoles have been shown to produce a local anesthetic effect. We used the whole-cell patch-clamp technique in this study to investigate whether tramadol blocks the sodium current in HEK293 cells, which stably express the pain threshold sodium channel Na_v1.7 or the cardiac sodium channel Na_v1.5. The half-maximal inhibitory concentration of tramadol was 0.73 mM for Na_v1.7 and 0.43 mM for Na_v1.5 at a holding potential of -100 mV. The blocking effects of tramadol were completely reversible. Tramadol shifted the steady-state inactivation curves of Na_v1.7 and Na_v1.5 toward hyperpolarization. Tramadol also slowed the recovery rate from the inactivation of Na_v1.7 and Na_v1.5 and induced stronger use-dependent inhibition. Because the mean plasma concentration of tramadol upon oral administration is lower than its mean blocking concentration of sodium channels in this study, it is unlikely that tramadol in plasma will have an analgesic effect by blocking Na_v1.7 or show cardiotoxicity by blocking Na_v1.5. However, tramadol could act as a local anesthetic when used at a concentration of several hundred millimoles by intradermal injection and as an antiarrhythmic when injected intravenously at a similar dose, as does lidocaine.

Inhibition of Fast Nerve Conduction Produced by Analgesics and Analgesic Adjuvants-Possible Involvement in Pain Alleviation

Nociceptive information is transmitted from the periphery to the cerebral cortex mainly by action potential (AP) conduction in nerve fibers and chemical transmission at synapses. Although this nociceptive transmission is largely inhibited at synapses by analgesics and their adjuvants, it is possible that the antinociceptive drugs inhibit nerve AP conduction, contributing to their antinociceptive effects. Many of the drugs are reported to inhibit the nerve conduction of AP and voltage-gated Na⁺ and K⁺ channels involved in its production. Compound action potential (CAP) is a useful measure to know whether drugs act on nerve AP conduction. Clinically-used analgesics and analgesic adjuvants (opioids, non-steroidal anti-inflammatory drugs, ₂-adrenoceptor agonists, antiepileptics, antidepressants and local anesthetics) were found to inhibit fast-conducting CAPs recorded from the frog sciatic nerve by using the air-gap method. Similar actions were produced by antinociceptive plant-derived chemicals. Their inhibitory actions depended on the concentrations and chemical structures of the drugs. This review article will mention the inhibitory actions of the antinociceptive compounds on CAPs in frog and mammalian peripheral (particularly, sciatic) nerves and on voltage-gated Na⁺ and K⁺ channels involved in AP production. Nerve AP conduction inhibition produced by analgesics and analgesic adjuvants is suggested to contribute to at least a part of their antinociceptive effects.

Effect of tramadol as an adjuvant to local anesthetics for brachial plexus block: A systematic review and meta-analysis

BACKGROUND

Tramadol, a 4-phenyl-piperidine analog of codeine, has a unique action in that it has a central opioidergic, noradrenergic, serotonergic analgesic, and peripheral local anesthetic (LA) effect. Many studies have reported contradictory findings regarding the peripheral analgesic effect of tramadol as an adjuvant to LA in brachial plexus block (BPB). This meta-analysis aimed to evaluate the effects of tramadol as an adjunct to LA in BPB during shoulder or upper extremity surgery.

METHODS

We searched the PubMed, EMBASE, Cochrane, KoreaMed databases, and Google Scholar for eligible randomized controlled trials (RCTs) that compared BPB with LA alone and BPB with LA and tramadol. Primary outcomes were the effects of tramadol as an adjuvant on duration of sensory block, motor block, and analgesia. Secondary outcomes were the effects of tramadol as an adjuvant on time to onset of sensory block and motor block and on adverse effects. We performed the meta-analysis using Review Manager 5.3 software.

RESULTS

We identified 16 RCTs with 751 patients. BPB with tramadol prolonged the duration of sensory block (mean difference [MD], -61.5 min; 95% CI, -95.5 to -27.6; P = 0.0004), motor block (MD, -65.6 min; 95% CI, -101.5 to -29.7; P = 0.0003), and analgesia (MD, -125.5 min; 95% CI, -175.8 to -75.3; P < 0.0001) compared with BPB without tramadol. Tramadol also shortened the time to onset of sensory block (MD, 2.1 min; 95% CI, 1.1 to 3.1; P < 0.0001) and motor block (MD, 1.2 min; 95% CI, 0.2 to 2.1; P = 0.010). In subgroup analysis, the duration of sensory block, motor block, and analgesia was prolonged for BPB with tramadol 100 mg (P < 0.05) but not for BPB with tramadol 50 mg. The quality of evidence was high for duration of analgesia according to the GRADE system. Adverse effects were comparable between the studies.

CONCLUSIONS

In upper extremity surgery performed under BPB, use of tramadol 100 mg as an adjuvant to LA appears to prolong the duration of sensory block, motor block, and analgesia, and shorten the time to onset of sensory and motor blocks without altering adverse effects.

The Analgesic Effects of Morphine and Tramadol Added to Intra-articular Levobupivacaine-Tenoxicam Combination for Arthroscopic Knee Surgery on Postoperative Pain; a Randomized Clinical Trial

BACKGROUND

Arthroscopic knee surgery is commonly performed as an outpatient procedure and is often associated with postoperative pain.

OBJECTIVES

We aimed to compare the effects of intra-articular levobupivacaine-tenoxicam-tramadol and levobupivacaine-tenoxicam-morphine combinations on postoperative pain in patients undergoing elective arthroscopic knee surgery.

MATERIALS AND METHODS

A total of 90 ASA I-II patients undergoing elective arthroscopic meniscectomy under general anesthesia were enrolled. The participants were randomly allocated to three groups to receive the following intra-articular medications after completion of the surgery and before deflation of the tourniquet: Group S, 20 mL of saline; Group T, 35 mg of levobupivacaine, 20 mg of tenoxicam, and 100 mg of tramadol in 20 mL saline; and Group M, 35 mg of levobupivacaine, 20 mg of tenoxicam, and 4 mg of morphine in 20 mL saline. Visual analogue scale values at rest (VASr) and at active flexion of knee (VASa) at postoperation hours 1, 2, 4, 8, 12, and 24, duration of analgesia, total analgesic consumption, and number of rescue analgesia at 24 hours were evaluated.

RESULTS

VASr and VASa were significantly higher in group S in comparison to other groups (P < 0.05). Duration of analgesia was significantly longer in Group T and Group M than in Group S (P < 0.05). The difference between group T and group M was also significant (P < 0.05). Number of rescue analgesia and total analgesic consumption at postoperative hour 24 was significantly fewer in group M compared with other groups (P < 0.05).

CONCLUSIONS

Intra-articular levobupivacaine-tenoxicam-morphine combination provides effective pain relief, longer analgesic duration, and less analgesic requirement when compared with intra-articular levobupivacaine-tenoxicam-tramadol combination and saline after knee arthroscopic surgery.

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.

Tramadol-induced blockade of delayed rectifier potassium current in NG108-15 neuronal cells

Tramadol is a centrally acting analgesic drug used mainly in the moderate to severe pain control. In this study, the effects of this agent on ion currents of NG108-15 neuronal cells were investigated. This cell line expresses Kv3.1a mRNAs and exhibits the activity of delayed rectifier K(+) (K(DR)) channels. Tramadol suppressed the amplitude of delayed rectifier K(+) current (I(K(DR))) in a concentration-dependent manner with an IC(50) values of 25 microM. Tramadol (30 microM) also shifted the steady-state inactivation of I(K(DR)) to a more negative membrane potential by approximately -15 mV. The role of the K(DR) channel, particularly as a member of the Kv3 superfamily, is to stabilize the resting potential and to reduce the width of action potentials in the time-coding neurons. Tramadol-induced block of I(K(DR)) observed in this study could be partly responsible for its anti-depressant action.

The maternal and neonatal effects of adding tramadol to 2% lidocaine in epidural anesthesia for cesarean section

Background:

Opioid analgesics are commonly added to epidural local anesthetics to improve analgesia during surgery.

Objectives:

The goal of this study was to evaluate the maternal and neonatal effects of adding different doses of tramadol to 2% lidocaine in the epidural anesthesia for cesarean section.

Patients and Methods:

Ninety pregnant patients who were candidates for cesarean section under epidural anesthesia were randomly categorized into three groups. Group L received 2% lidocaine. In the LT50 and LT100 groups, 50 and 100 mg of tramadol were added to epidural 2% lidocaine. For additional analgesia during surgery, 2% lidocaine through epidural catheter or IV sufentanil were administered. Analgesia after surgery was provided by IV injection of meperidine. Onset and duration of sensory and motor blockades, total drug consumption, neonatal Apgar score, and complications were recorded.

Results:

In the LT100 group, onset of complete sensory and motor blockade at T6 was less than in the two other groups, but the highest level of sensory blockade and two segment regression and duration of motor blockades between the LT50 and LT100 groups were not significantly different, although they were higher and more prolonged than in the L group. Average lidocaine and sufentanil consumption during surgery between the LT50 and LT100 groups were not significantly different but were lower than in the L group. The incidence of maternal complications and neonatal Apgar scores were not significantly different between the three groups. In the LT50 and LT100 groups, the time until the first request for analgesics after surgery was prolonged, and average meperidine consumption was less than in the L group.

Conclusions:

The addition of tramadol to epidural 2% lidocaine offers advantages in cesarean section.

Tramadol use for axillary brachial plexus blockade

BACKGROUND

We investigated the effects of tramadol added to the mixture of local anesthetic for axillary brachial plexus blockade (ABB) in patients to have undergone hand and forearm surgery.

MATERIALS AND METHODS

Forty patients from the ASA classification I and II, between 18 and 60 y of age, were included in this randomized double-blind study. Group C: levobupivacaine (150 mg) + lidocaine (200 mg) (n = 20), Group T: levobupivacaine (150 mg), + lidocaine (200 mg) + tramadol (100 mg) (n = 20). Intravenous midazolam of 0.02 mg/kg was given for premedication. ABB was performed with 42 mL mixture of local anesthetic, using peripheral nerve stimulator. The duration of onset of motor and sensory blockades was recorded. The postoperative first analgesic need, sedation, and satisfaction score and side effects were recorded.

RESULTS

There was no significant difference between the groups regarding intraoperative visual analog scale (VAS), hemodynamics, adverse effects, sedative and analgesic requirement, and the patient satisfaction. The development of motor block at the median nerve on the 5th min (P = 0.03) and at the ulnar nerve on 10th and 15th min in Group T were (P = 0.01, P = 0.03, respectively) considerably longer than that in Group C.

CONCLUSIONS

Adding 100 mg of tramadol to the combination of levobupivacaine and lidocaine during ABB could not provide an important clinical effect in patients undergoing hand and forearm surgery.

Effect of pulsed magnetic field on regenerating rat sciatic nerve: An in-vitro electrophysiologic study

Some experimental studies report that low-frequency pulsed electromagnetic field (PEMF) stimulation may accelerate regeneration in peripheral nerves. In the present study, effects of PEMF on the regeneration of the crushed rat sciatic nerves were investigated with histological and in-vitro electrophysiological methods (sucrose-gap). After crush injury of the sciatic nerves, rats were divided into 5, 15, 25, 38 day-groups and exposed to PEMF (1.5 h/day, intensity; 1.5 mT, consecutive frequency; 10-40-100 Hz). In the 15th day post crush, compound action potential (CAP) amplitude was measured as 5.5+/-1 mV (crush group) and 5.4+/-1.2 mV (crush+PEMF group). In addition, half width of CAP extended ~3 fold in both groups and frequency-dependent amplitude inhibition (FDI) decreased approximately 20% at 100 Hz. In the 38th day, amplitude of CAP, half width of CAP and FDI were measured nearly intact nerve values in both groups. In histological examinations, Wallerian degeneration was observed similar progress between both groups. The results were compared between crush and crush + PEMF groups, it was found that the effect of PEMF was not significant. The authors conclude that PEMF were ineffective on rat sciatic nerve regeneration.

Intraarticular tramadol-bupivacaine combination prolongs the duration of postoperative analgesia after outpatient arthroscopic knee surgery

BACKGROUND

Intraarticular (IA) local anesthetics are often used for the management and prevention of pain after arthroscopic knee surgery. Recently, IA tramadol was also used for the management of these patients. However, the IA combination of local anesthetic and tramadol has not been evaluated in arthroscopic outpatients. Our primary aim in this study was to evaluate the analgesic effect of an IA combination of bupivacaine and tramadol when compared with each drug alone using visual analog scale (VAS) pain scores in patients undergoing day-care arthroscopic knee surgery. Additionally, we assessed analgesic demand.

METHODS

Ninety ASA I/II patients undergoing arthroscopic partial meniscectomy, performed by a single surgeon under general anesthesia, were assigned in a randomized, double-blind manner into three groups: group B (n = 30) received 0.25% bupivacaine, group T (n = 30) received 100 mg tramadol, and group BT (n = 30) received 0.25% bupivacaine and 100 mg tramadol to a total volume of 20 mL by the IA route after surgery. Postoperative pain scores were measured on a VAS, at rest and on mobilization at 0.5, 1, 2, 4, 6, 8, 12, and 24 h. Duration of analgesia, the subsequent 24 h consumption of rescue analgesia, time to ambulation, and time to discharge were evaluated. In addition, the systemic side effects of the IA injected drugs were also assessed.

RESULTS

The results showed significantly lower VAS pain scores in group BT (P << 0.1) when compared with groups T and B. Group BT had a later onset of postsurgical pain and longer time to first rescue analgesic than groups B and T. The 24 h consumption of analgesic was significantly less in group BT when compared with the other two groups (26.7% of the patients required rescue analgesia in group BT, whereas this number was 90% in group B and 86.7% in group T). In addition, time in hours to discharge and time to unassisted ambulation were significantly shorter in group BT when compared with groups T and B, and this was not associated with any detectable systemic effects.

CONCLUSION

The IA admixture of tramadol 100 mg with bupivacaine 0.25% provides a pronounced prolongation of analgesia compared with either drug alone in patients undergoing day care arthroscopic knee surgery.

Inhibitory effect of tramadol on vasorelaxation mediated by ATP-sensitive K+ channels in rat aorta

PURPOSE

Tramadol produces a conduction block similar to lidocaine by exerting a local anesthetic-like effect. The aims of this in vitro study were to determine the effects of tramadol on the vasorelaxant response induced by the adenosine triphosphate-sensitive K(+) (K(ATP)) channel opener, levcromakalim, in an endothelium-denuded rat aorta, and to determine whether this effect of tramadol is stereoselective.

METHODS

The effects of tramadol (racemic, R(-) and S(+): 10(-6), 10(-5), 5 x 10(-5) M), and glibenclamide on the levcromakalim dose-response curve were assessed in aortic rings that had been pre-contracted with phenylephrine. In the rings pretreated independently with naloxone, and glibenclamide, the levcromakalim dose-response curves were generated in the presence or absence of tramadol. The effect of tramadol on the dose-response curve of diltiazem was assessed.

RESULTS

Racemic, R(-) and S(+) tramadol (10(-5), 5 x 10(-5) M) attenuated (P < 0.0001) levcromakalim-induced relaxation in the ring with or without naloxone in a dose-dependent manner. The magnitude of the R(-)-tramadol-induced attenuation of vasorelaxant response induced by levcromakalim was greater (P < 0.05) than that induced by S(+)-tramadol. Glibenclamide almost abolished the levcromakalim-induced relaxation. Tramadol, 5 x 10(-5) M, did not significantly alter the diltiazem-induced relaxation.

CONCLUSION

These results suggest that a supraclinical dose (10(-5) M) of tramadol [racemic, R(-) and S(+)] attenuates the vasorelaxation mediated by the K(ATP) channels in the rat aorta. The R(-) tramadol-induced attenuation of vasorelaxation induced by levcromaklim was more potent than that induced by S(+) tramadol. This attenuation is independent of opioid receptor activation.

Tramadol, fentanyl and sufentanil but not morphine block voltage-operated sodium channels

Lidocaine-like sodium channel blocking drugs provide pain relief either by interrupting impulse conduction in neurons when applied locally in high concentrations or, when given systemically, by suppressing high-frequency ectopic discharges due to preferential drug binding to inactivated channel states. Lidocaine-like actions of opioids have frequently been demonstrated clinically. However, drug binding to resting and inactivated channel conformations has been studied systematically only in the case of meperidine. The aim of this in vitro study was to investigate the effects of four currently used opioids on heterologously expressed neuronal (NaV(1.2)) voltage-gated sodium channels. Block of sodium currents was studied at hyperpolarized holding potentials and at depolarized potentials inducing either fast- or slow-inactivation. Sufentanil, fentanyl and tramadol but not morphine reversibly suppressed sodium inward currents at high concentrations (half-maximum blocking concentrations (IC50) 49+/-4, 141+/-6 and 103+/-8 microM) when depolarizations were started from hyperpolarized holding potentials. Short depolarizations inducing fast-inactivation and long prepulses inducing slow-inactivation significantly (*p < or = 0.001) increased the blocking potency for these opioids. 15% slow inactivated channels reduced the respective IC50 values to 5+/-3, 12+/-2 and 21+/-2 microM. These results show that: (1) Sufentanil, fentanyl and tramadol block voltage-gated sodium channels with half-maximum inhibitory concentrations similar to the IC50 reported for meperidine. (2) Slow inactivation--a physiological mechanism to suppress ectopic activity in response to slow shifts in membrane potential--increases binding affinity for sufentanil, fentanyl and tramadol. (3) Morphine has no such effects.

Tramadol, but not its major metabolite (mono-O-demethyl tramadol) depresses compound action potentials in frog sciatic nerves

BACKGROUND AND PURPOSE

Although tramadol is known to exhibit a local anaesthetic effect, how tramadol exerts this effect is not understood fully.

EXPERIMENTAL APPROACH

The effects of tramadol and its metabolite mono-O-demethyl-tramadol (M1) on compound action potentials (CAPs) were examined by applying the air-gap method to frog sciatic nerves, and the results were compared with those of other local anaesthetics, lidocaine and ropivacaine.

KEY RESULTS

Tramadol reduced the peak amplitude of the CAP in a dose-dependent manner (IC50=2.3 mM). On the other hand, M1 (1-2 mM), which exhibits a higher affinity for mu-opioid receptors than tramadol, did not affect CAPs. These effects of tramadol were resistant to the non-selective opioid receptor antagonist naloxone and the mu-opioid receptor agonist, DAMGO, did not affect CAPs. This tramadol action was not affected by a combination of the noradrenaline uptake inhibitor, desipramine, and the 5-hydroxytryptamine uptake inhibitor, fluoxetine. Lidocaine and ropivacaine also concentration-dependently reduced CAP peak amplitudes with IC50 values of 0.74 and 0.34 mM, respectively.

CONCLUSIONS AND IMPLICATIONS

These results indicate that tramadol reduces the peak amplitude of CAP in peripheral nerve fibres with a potency which is less than those of lidocaine and ropivacaine, whereas M1 has much less effect on CAPs. This action of tramadol was not produced by activation of mu-opioid receptors nor by inhibition of noradrenaline and 5-hydroxytryptamine uptake. It is suggested that the methyl group present in tramadol but not in M1 may play an important role in producing nerve conduction block.

Comparative effects of lidocaine and tramadol on injured peripheral nerves

The aim of the present study was to investigate the action of lidocaine and tramadol on the abnormal impulse characteristics of injured peripheral nerves. The ultrastructure of nerves was studied with electron microscopy and the action of lidocaine and tramadol on intact and injured rat sciatic nerves was examined by using the sucrose gap recording technique. Tramadol and lidocaine caused concentration- and frequency-dependent decreases in the amplitude of the compound action potential. Injured nerves were more sensitive to lidocaine than to tramadol. Lidocaine suppressed the delayed depolarization and decreased the hyperpolarizing afterpotentials to a greater extent than did tramadol. A low concentration of lidocaine may restore the abnormal impulse characteristics of injured nerves without changing the normal impulse pattern. The efficacy of lidocaine and inefficacy of tramadol on abnormal impulse characteristics may contribute, at least in part, to our understanding of the mechanisms of action of these drugs in neuropathic pain therapy.

Effects of tramadol on nerve action potentials in rat: comparisons with benzocaine and lidocaine

The effects of tramadol on repetitively elicited action potentials were studied in rat sciatic nerve, using the sucrose gap method. Tramadol's local anesthetic-like effects were compared with lidocaine and benzocaine at single or 10, 40, and 100 Hz stimulations. Tramadol and lidocaine both produced approximately the same level of conduction block. The depolarization time of the compound action potentials (CAP) measured from the beginning to the peak of the CAPs, was extended by lidocaine and tramadol, but benzocaine had no effect in this respect. Tramadol extended half width of CAP more than lidocaine. Lidocaine and tramadol produced similar conduction-block patterns, which were different from benzocaine. The results suggested that tramadol enhanced the nerve conduction like lidocaine. However, their frequency-dependent block patterns were similar. It was concluded that tramadol may block the Na+ channels following the hydrophilic pathway like lidocaine and block K+ channels more than lidocaine. These may accounted for the local anesthetic-like effects of tramadol.

Tramadol as adjunct to psoas compartment block with levobupivacaine 0.5%: a randomized double-blinded study

BACKGROUND

Tramadol has been administered peripherally to prolong analgesia after brachial plexus and neuraxial blocks. Our aim was to evaluate the systemic and perineural effects of tramadol as an analgesic adjunct to psoas compartment block (PCB) with levobupivacaine.

METHODS

In a randomized, prospective, double-blinded trial, 60 patients (ASA I-III), aged 49-88 yr, undergoing primary total hip or knee arthroplasty underwent PCB and subsequent bupivacaine spinal anaesthesia. Patients were randomized into three groups. Each patient received PCB with levobupivacaine 0.5%, 0.4 ml kg(-1). The control group (group L, n=21) received i.v. saline, the systemic tramadol group (group IT, n=19) received i.v. tramadol 1.5 mg kg(-1) and the perineural tramadol group (group T, n=20) received i.v. saline and PCB with tramadol 1.5 mg kg(-1). Postoperatively patients received regular paracetamol 6-hourly and diclofenac sodium 12-hourly. Time to first morphine analgesia, 24-hour morphine consumption, sensory block, pain and sedation scores and haemodynamic parameters were recorded.

RESULTS

Time (h) to first morphine analgesia was similar in the three groups [mean (SD)]: group L, 11.2 (6.6); group T, 14.5 (8.0); group IT, 14.6 (6.8); P=0.35. Twenty-four-hour cumulative morphine (mg) consumption was also similar in the three groups [group L, 21.9 (10.1); group T, 19.8 (6.7), group IT, 16.5 (9.5)], as were durations of sensory and motor block. There were no differences in the incidence of adverse effects except that patients in group IT were more sedated at 14 h than group L (P=0.02).

CONCLUSION

We conclude that our data do not support a clinically important local anaesthetic or peripheral analgesic effect of tramadol as adjunct to PCB with levobupivacaine 0.5%.

Role of Potassium Channels in the Frequency-Dependent Activity of Regenerating Nerves

After a peripheral nerve injury, ion channel organization and the electrical properties of nerve fibers drastically change during the regeneration process. The present study was designed to compare the frequency-dependent characteristics of regenerating nerves in the presence of 4-aminopyridine (4-AP) and tetraethylammonium (TEA). The results showed that increasing the stimulus frequency produced a greater impulse blockade (frequency-dependent block--FDB) and distinct hyperpolarizing afterpotentials (HAPs) in regenerating nerves. In particular, regenerating sciatic nerves 15 days post-crush (dpc) were more sensitive to the frequency-dependent stimulations than 38-dpc and intact nerves in the presence or absence of drugs. The frequency-dependent effects of TEA on the compound action potentials (CAPs) appeared when TEA was applied to 4-AP-treated nerves. This shows that TEA-sensitive channels may not be masked by the myelin. 4-AP was here found to have more pronounced frequency-dependent effects on regenerating nerves than on intact nerves. Delayed depolarization (in 38-dpc: 22.6 +/- 1.3 mV and 47.52 +/- 3.63 ms, in intact: 12.0 +/- 1.9 mV and 88.51 +/- 4.72 ms) elicited by 4-AP resulted in an increase in FDBs and HAP amplitudes. These results suggest that 4-AP-sensitive channels may play important roles in frequency-dependent nerve conduction. Consequently, regenerating or myelin damaged nerves are more sensitive to repetitive firing with or without drug. An understanding of the frequency-dependent properties of regenerating nerves may be of value in the treatment of the nerve diseases.

Changes in electrophysiological properties of regenerating rat peripheral nerves after crush injury

The conduction of action potential in peripheral nerves requires the coordinated opening and closing of Na(+) and K(+) channels. In the present study, we used the sucrose-gap recording technique to determine the electrophysiological changes of the regenerating nerves after sciatic nerve injury by using 4-aminopyridine (4-AP) and tetraethylammonium (TEA), and lidocaine. 4-AP enhanced the amplitude and duration of the compound action potentials (CAPs) of regenerating sciatic nerve 15 days post crush (15 dpc), and elicited delayed depolarizations (Del-dep) in 38 dpc and intact groups. Hyperpolarizing afterpotentials elicited by 4-AP were completely removed by TEA in both 15 and 38 dpc. Lidocaine effectively blocked the CAP amplitude. This blockage was more pronounced in 15 dpc than 38 dpc. This agent also exhibited a partial blockage on the Del-dep amplitude. These results may indicate that the changes in the activities of 4-AP- and TEA-sensitive K(+) channels and slow Na(+) channels may play critical roles in nerve excitability and conduction.