Potent and long lasting antinociceptive effects after injection of low doses of a mu-opioid receptor agonist, fentanyl, into the brachial plexus sheath of the rat

Intradermal sufentanil does not improve lidocaine-induced local anesthesia

PURPOSE

Peripheral opioid receptors may result in antinociceptive effects when occupied by opioids. This study examined intradermally injected sufentanil (S), a highly lipid soluble opioid, administered with and without lidocaine (L), in a thermal pain model.

METHODS

Nine volunteers were instructed on the method of magnitude estimation of pain before undergoing baseline testing with seven seconds thermal stimuli between 44 and 52 degrees C, delivered by a contact thermal stimulator at five cutaneous forearm sites. Then, four sites randomly received injections of equal volumes (0.1 mL) of either normal saline (NS), lidocaine 0.5% (L), sufentanil 0.75 microg (S), lidocaine 0.5% plus sufentanil 0.75 microg (L+S), and one site was not injected and served as reference (REF). Testing was repeated at six, 30, 60, 90, 120, and 150 min following injection. The pain elicited by each stimulus was normalized to the subject's response to the 50 degrees C stimulus at the REF site.

RESULTS

Baseline testing showed small (P = ns) differences in pain scores. At six minutes, the lidocaine sites (L, L+S) had pain scores that were mean 83% (range 78-88%) lower than the other sites (P < 0.05), but there was no difference between the L and L+S sites or between the S and NS or REF sites. At 30 and 60 min these pain scores were mean 38% (29-44%) and 20% (8-30%) less than at the REF, NS, and S sites (P = ns). At 90 min and later times, the pain scores had returned to baseline.

CONCLUSIONS

These results suggest that intradermal sufentanil alone has no analgesic effect. Further, in combination with lidocaine, sufentanil does neither potentiate nor prolong the analgesic effect of lidocaine.

Perineural antinociceptive effect of opioids in a rat model

BACKGROUND

The research on conductive analgesia induced by perineural opioids generated a large body of conflicting data. In this study we reassessed the antinociceptive response to perineural administration of morphine, fentanyl or meperidine in a rat model.

METHODS

Analgesia was assessed using the hind paw withdrawal latency (HPWL) response to radiant heat. The opioid dose producing 20% of maximal possible effect (20%MPE) for systemic analgesia was calculated for each drug. Then sciatic blockade was performed with the dose corresponding to 20%MPE. The injected hind paw was used to measure direct perineural effect and the contralateral hind paw was used as an indicator of systemic effect.

RESULTS

The response latency produced by morphine or fentanyl was not significantly different for ipsilateral (perineural effect) or contralateral (systemic effect) paw (27+/-11 vs. 28+/-16 and 3l+/-16 vs. 23+/-16 s, respectively). However, the meperidine group showed significantly higher %MPE for the ipsilateral paw (79+/-32 s) than for the contralateral paw (27+/-22 s).

CONCLUSIONS

The results indicate that perineural fentanyl or morphine do not produce analgesia. Perineural block produced by meperidine was attributed to local anesthetic-like effect, rather than to drug interaction with opioid receptor.

Sufentanil does not prolong the duration of analgesia in a mepivacaine brachial plexus block: a dose response study

To date, results of studies evaluating the efficacy of opioids and local anesthetic combinations in the brachial plexus are inconclusive. We examined whether increasing sufentanil in doses of 5, 10, and 20 microg decreased onset time or increased duration of an axillary brachial plexus block. Ninety-two patients scheduled for carpal tunnel release under axillary brachial plexus block were enrolled in the study. Patients were randomized to receive axillary plexus block with 40 mL 1.5% mepivacaine and saline (Group 1), sufentanil 5 microg (Group 2), 10 microg (Group 3), or 20 microg (Group 4). Onset and duration of sensory and motor block were measured. Opioid-related side effects were recorded. The addition of sufentanil did not improve speed of onset or increase the duration of sensory or motor block. Paradoxically, duration of sensory and motor block was longest in the control group: sensory, 241 min (188-284) and motor, 234 min (128-305), and decreased with increasing doses of sufentanil in Group 4: sensory, 216 min (115-315) and motor, 172 min (115-260) (P < 0.05). Side effects occurred in 55% of patients belonging to Groups 2 and 4, and in 60% of the patients in Group 3. In contrast, only 10% of the patients reported side effects in the control group. We conclude that sufentanil added to mepivacaine does not increase the onset or prolong the duration of an axillary plexus block. Furthermore, the addition of sufentanil was associated with a frequent incidence of side effects.

IMPLICATIONS

This study demonstrates that the addition of sufentanil in a dose-dependent manner to 1.5% mepivacaine in the axillary plexus does not improve onset or duration of blockade, and that this admixture is associated with an increased incidence of side effects.

Peripheral component in the enhanced antinociceptive effect of systemic U-69,593, a kappa-opioid receptor agonist in mononeuropathic rats

The contribution of a peripheral action of the kappa-opioid receptor agonist U-69,593 (trans-3,4-dichloro-N-methyl-N-[7-(1-pyrrolidinyl) cycloexil] benzene-acetamide methanesulfonate) in the augmented antinociceptive effect of this substance was investigated in a well-established rat model of peripheral unilateral neuropathy (chronic constriction of the common sciatic nerve). Relatively low dose of systemic U-69,593 (0.75 mg/kg intravenous (i.v.)) and intraplantar (i.pl.) low doses of specific antagonists of kappa-(nor-binaltorphimine) or mu-(D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2: CTOP) opioid receptors were used. Vocalization thresholds to paw pressure were used as a nociceptive test. The i.pl. injection of nor-binaltorphimine (10-15 microg injected into the nerve-injured hind paw) had no effect on the antinociceptive effect of U-69,593. Higher doses (20-30 microg i.pl. nor-binaltorphimine) significantly reduced the effect of U-69,593 on this paw but not on the contralateral paw, an effect which plateaued at 30 microg. By contrast, the i.pl. injection of CTOP (1 microg into the nerve-injured paw) had no effect on U-69,593 antinociception, whereas it reduced the effect of systemic morphine in these animals. The doses of nor-binaltorphimine used, injected into the contralateral paw or i.v., failed to modify the antinociceptive effects of U-69,593 on either paw. These results provide evidence for a peripheral component in the enhanced antinociceptive effect of systemic U-69,593 in this model of neuropathic pain.

Changes in plasma cortisol concentrations in bitches in response to different combinations of halothane and butorphanol, with or without ovariohysterectomy

Changes in plasma cortisol concentrations were assessed in bitches in response to nine treatments: control, anaesthesia, analgesia, analgesia followed by anaesthesia, anaesthesia followed by analgesia at intubation, anaesthesia followed by analgesia at extubation, anaesthesia plus surgery, analgesia followed by anaesthesia plus surgery, and anaesthesia plus surgery followed by analgesia. The anaesthetic was halothane, the analgesic was butorphanol (0.4 mg kg(-1)) and the surgery was ovariohysterectomy. Blood samples, for plasma cortisol assays, were taken regularly from before treatment for five hours and then again after 24 hours. A small transient rise in plasma cortisol concentration in the control group was attributed to mild distress associated with novel experiences. A more pronounced and protracted rise in cortisol concentration in the analgesia group was ascribed to a dysphoric state of bitches under the influence of the agonist-antagonist butorphanol. Halothane anaesthesia alone resulted in no change in plasma cortisol concentration. When butorphanol was given after anaesthesia was induced or while the animal was still under the influence of anaesthesia (immediately after tracheal extubation), there was no immediate rise in plasma cortisol concentration and low concentrations were maintained for up to 60 minutes after halothane withdrawal. A marked rise in plasma cortisol concentration, which was sustained above pretreatment values for at least five hours, occurred in all surgery groups. Giving intravenous butorphanol 30 minutes prior to surgery had no effect on the surgically-induced rise in plasma cortisol concentration and no effect on the postsurgical plasma cortisol concentration. In contrast, butorphanol given at extubation did reduce plasma cortisol concentrations during the postsurgical period. These observations did not support the hypothesis that preoperative use of butorphanol would reduce the cortisol response after surgery under halothane anaesthesia.

[Brachial plexus block: effect of the addition of sufentanil to local anesthetic mixture on postoperative analgesia duration]

OBJECTIVES

To compare the quality and the duration of analgesia produced by a supraclavicular brachial plexus blockade obtained with a mixture of lidocaine and bupivacaine when supplemented or not with sufentanil.

STUDY DESIGN

Prospective, randomized, double-blind study.

PATIENTS

The study included 40 patients undergoing osteosynthesis of the upper limb under brachial plexus block, randomly assigned to two groups.

METHODS

The patients of the control group were given 0.5% bupivacaine 1 mg.kg-1 and 1% lidocaine 2 mg.kg-1. Those of the sufentanil group, received the same mixture supplemented with sufentanil 0.2 mg.kg-1. During the postoperative period, the characteristics of analgesia were blindly evaluated every hour for 48 h with a visual analogic scale graduated from 0 to 100. Analgesia was considered satisfactory when the score was below 30. Adverse effects of opiates (drowsiness, pruritus, nausea and vomiting) were also assessed. Oxygen saturation was continuously monitored. Blood pressure, heart and respiratory rates were measured at the same intervals than analgesia. Duration of analgesia are expressed as medians (range) and compared using a Mann and Whitney's U test.

RESULTS

The respective durations of satisfactory analgesia were significantly different: 12.5 h (8-17) in the control group versus 24 h (8-48) for the sufentanil group. The adverse effects in the sufentanil group were nausea (2), vomiting (1) and pruritus (1). No respiratory depression was noted.

CONCLUSION

Sufentanil added to a mixture of lidocaine and bupivacaine increases twofold the duration of postoperative analgesia following branchial plexus blockade.

The reorganization of mu opioid receptors in the rat dorsal horn following peripheral axotomy

The mu opioid receptor is concentrated in laminae I and II (LI and LII, respectively) of the normal rat dorsal horn. Fourteen days after transection of the L4-L6 segmental peripheral nerves, image analysis demonstrates a 49, 34 and 17% decrease in mu opioid staining density in the medial, middle and lateral thirds of the superficial dorsal horn, respectively, when comparing the operated to the unoperated side. Intralaminar analysis demonstrates that the greatest change in density occurs in LI and LII outer, compared to LII inner. By 31 days post-surgery, staining has returned to normal with side to side differences no longer present. These results imply that mu opioid ligands such as morphine might be less effective in ameliorating pain 2 weeks after a peripheral nerve lesion than they are in the normal condition, but that this effectiveness should return as the receptors are restored to their normal levels. Thus, the time following a lesion may be an important variable in assessing the effectiveness of mu opioid ligands in alleviating neuropathic pain. Furthermore, this study shows that the organization of opioid receptors in the superficial dorsal horn is malleable and could lead to changes in drug efficacy.

Opioid receptors on peripheral sensory axons

Opioid receptors have been demonstrated by light microscopic techniques in fine cutaneous nerves in naive animals. The present study extends these findings by showing that 29 and 38% of unmyelinated cutaneous sensory axons can be immunostained for mu- or delta-opioid receptors respectively. Local cutaneous injection of DAMGO, a mu-opioid ligand, ameliorates the nociceptive behaviors caused by local cutaneous injection of glutamate, a purely nociceptive chemical stimulus showing that the mu-receptors are functional. By contrast the delta-opioid ligand [2-D-penicillamine, 5-D-penicillamine]enkephalin (DPDPE) had no effect on these behaviors. These findings indicate a wider function for opioid receptors in naive animals than previously envisioned.

Intratracheal administration of fentanyl: pharmacokinetics and local tissue effects

OBJECTIVE

To study the pharmacokinetics and local tissue effects resulting from the intratracheal administration of preservative-free fentanyl.

DESIGN

Prospective, randomized, blinded and controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Eighteen adult male New Zealand rabbits.

INTERVENTIONS

Preservative-free fentanyl citrate or normal saline was administered by the intratracheal (i.t.) and intravenous (i.v.) routes to randomized groups of rabbits. The animals were killed at 24, 48 and 72 h following administration.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations of fentanyl were measured before administration and at 2, 5, 10, 30, 60 and 120 min following administration by a specific radioimmunoassay. A detailed histological examination of the lung and tracheal tissue was performed to identify local side effects. There were no significant differences in the plasma fentanyl concentrations resulting from the i.v. or i.t. route of administration. In both groups, the concentrations of fentanyl were within the therapeutic range (i.t. 2.37 ng/ml, i.v. 2.53 ng/ml) by 2 min after injection and reached a maximum concentration within 5 min. The bioavailability of i.t. fentanyl was 71%. Microscopic examination of the respiratory system did not show significant differences between the two random groups overall. However, in the sub-group of animals killed at 24 h, more animals in the i.t. group showed signs of inflammation in the lung parenchyma.

CONCLUSIONS

There is rapid absorption of fentanyl following i.t. administration. Pharmacokinetic parameters for fentanyl were not significantly altered by the route of administration. Although there were no signs that i.t. administration of preservative-free fentanyl produces lung injury, a transient and mild inflammatory response was detected at 24 h after administration.

An evaluation of the antiinflammatory effects of intraarticular synthetic beta-endorphin in the canine model

We sought to evaluate the antiinflammatory effects of synthetic human beta-endorphin (SHB) when injected into the canine knee joint. Sixteen healthy dogs, aged 1-2 yr, were selected. SHB was injected pre- and postinjury into each knee. The sample size was n = 32 after a randomized factorial arrangement; 2 x 4 with four cases per treatment being performed. Factors considered were: Factor A with two levels: A1 = Preinjury and A2 = Postinjury; Factor B (SHB dose) with four levels: B1 = Control, B2 = 250 micrograms, B3 = 500 micrograms, B4 = 1000 micrograms. The control group received 0.9% NaCl solution. Anesthesia was induced with intravenous thiopental, 14 mg/kg, and acepromazine, 0.5 mg/kg. Injury was produced with an intraarticular injection of 4 mL HCl 0.5 M, which was left in situ for 20 min. Inflammation was measured using the 610 nm absorbency of Evans blue extravasate in biopsy specimens. Histopathologic studies were performed on each knee. We found that beta-endorphin has a clear, dose-related, antiinflammatory effect, reducing the tissue extravasation of Evans blue and its absorbency, especially with large doses. This finding was consistent with the histopathologic observations. We conclude that SHB has an antiinflammatory effect. It is still not clear which mechanisms inhibit polymorphonuclear cell adhesion to vascular endothelium or cell and plasmatic protein extravasation.

Evidence for a peripheral component in the enhanced antinociceptive effect of a low dose of systemic morphine in rats with peripheral mononeuropathy

In a rat model of peripheral mononeuropathy produced by moderate constriction of the sciatic nerve, we have shown that various i.v. doses of morphine and selective opioid agonists produce potent and long-lasting antinociceptive effects on the vocalization threshold to paw pressure. For all the opioids, the antinociceptive effects were more marked for the paw on the nerve-injured side (nerve-injured paw) than for the sham-operated paw. One contributory mechanism could be a peripheral action of the opioid agonists in the nerve-injured paw. This hypothesis was tested in the present study, using systemic morphine and low doses of local naloxone or its quaternary salt naloxone methiodide, exhibiting peripherally acting antagonist properties. The effects of escalating doses of naloxone (0.5-2 microgram injected i.v. or intraplantar into the nerve-injured paw) or naloxone methiodide (5-30 micrograms into the nerve-injured paw) on the antinociceptive effect of morphine (1 mg/kg i.v.) were evaluated using the vocalization threshold to paw pressure in neuropathic rats at two weeks after placing ligatures, a time when the behavioural pain-related disorders have reached a maximum.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced potency of intravenous, but not intrathecal, morphine and morphine-6-glucuronide after burn trauma

We examined the analgesic effect of morphine (M) and its metabolite morphine-6-glucuronide (M6G) in a rat model of acute thermal trauma. M or M6G were given by intrathecal (IT) or intravenous (i.v.) routes after brief burn or sham burn delivered during inhalational anesthesia. In the sham group, M6G was significantly less potent than M when given i.v., yet tended to be more potent than M when given IT. For both drugs, thermal injury increased i.v. potency, yet decreased (for M) or displayed a trend to decrease (for M6G) It potency. The increased potency seen with i.v. but not IT opioid administration may reflect pharmacokinetic (e.g., diminished clearance) and/or pharmacodynamic responses (e.g., activation of peripheral opioid receptors) after thermal injury.

[New modes of opioid administration.]

In the last few years great interest has developed in new modes of opioid administration; oral transmucosal, transdermal, peripheral, and nasal administration.Oral transmucosal administration of fentanyl citrate (OTFC) has most often been used for premedication in children. Meanwhile, studies on the use of OTFC in cancer patients for postoperative pain management have also been published. While OTFC may have a limited role in postoperative pain management, it may prove very helpful in the management of incident and breakthrough cancer pain. Patient acceptance is high, and the onset of action is relatively rapid.Transdermal administration of fentanyl (TTS fentanyl) has been extensively examined, especially in postoperative patients. Patient acceptance is high, and TTS-fentanyl-related side-effects (e.g. mild erythema at the site of application) are minor. Application is performed at 72-h intervals. Kinetics are stable with repeated dosing, and serum concentrations approach steady state with the first dose. The slow rise/decline in fentanyl plasma concentration with patch application/removal makes it less well suited for postoperative pain management. However, TTS fentanyl seems to be a promising mode of opioid administration for cancer patients.-Recent papers have unequivocally demonstrated a peripheral antinociceptive effect oflocally applied opioids, especially in inflamed tissue. However, the results of clinical investigations are equivocal so far: about half the reports demonstrate an analgesic effect of peripherally administered opioids, and the other half, not.Intranasal administration was introduced for premedication in children, but benzodiazepines seem to be the better and safer choice. Nonetheless, intranasal opioids guarantee a rapid rise in opioid plasma concentrations as well as a rapid onset of pain relief. This mode of administration seems to be especially suitable for the treatment of acute pain syndromes, such as breakthrough cancer pain or incident pain. Patient acceptance is high, and no local problems were reported.

[Respiratory response to carbon dioxide after brachial plexus block with fentanyl and lidocaine]

Respiratory parameters, ventilatory response to carbon dioxide and quality of anaesthesia were studied in patients undergoing upper limb surgery under axillary blockade. Thirteen patients were randomly assigned to two groups, group A (n = 6), who were given 35 ml of 1.5% lidocaine with 1 in 200,000 of adrenaline, and group B (n = 7), who received 1 microgram.kg-1 of fentanyl with the same dose of lidocaine. Quality of the sympathetic, sensory and motor blocks were tested at 15 min (T1) and 45 min (T2) after the injection (T0). The other parameters measured at these three times, both with the patient in a half-sitting position breathing room air, and after a rebreathing test with CO2 through Read's circuit, were respiratory rate (FR), tidal volume (VT), minute ventilation (VE), and PetCO2. Fentanyl provided a better sensory and motor blockade at T1, without any difference in sympathetic blockade. The quality of the blocks was similar in both groups at T2. There were no significant differences in the respiratory parameters between the two groups. Moreover, there was no untoward effect due to fentanyl (nausea, pruritus). It is concluded that 1 microgram.kg-1 fentanyl added to a local anaesthetic solution may be useful, at least during the first hour of an axillary block, without any respiratory side-effects.

Evidence for analgesia mediated by peripheral opioid receptors in inflamed synovial tissue

Intra-articular morphine (5 mg in 25 ml) was administered to patients for post-operative analgesia following arthroscopic knee surgery. At various time intervals, 30 min to 4 h post morphine, venous blood samples were taken in order to determine plasma levels of morphine and its primary metabolites, morphine-3-glucuronide and morphine-6-glucuronide. Measurable amounts of morphine and morphine-3-glucuronide were found in the plasma of 7/10 patients whereas morphine-6-glucuronide was detected in only 2/10 patients. The plasma levels of morphine were lower than that regarded sufficient for post-operative analgesia in all but two patients, indicating a possibility of peripheral analgesia. In addition, synovial biopsy samples were assayed for the presence of opioid binding sites. Tissue samples from 11 different patients were analysed and 6/11 exhibited specific binding of [3H]naloxone, indicating the presence of opioid binding sites/receptors. The receptor type (i.e. mu-, delta- or k-) is at present unknown. Taken together, these data provide evidence that locally administered opiates can act on specific opioid receptors in the synovium to mediate analgesia.

Behavioural evidence for a peripheral component in the enhanced antinociceptive effect of a low dose of systemic morphine in carrageenin-induced hyperalgesic rats

This study reinvestigated the possible contribution of a peripheral action of systemic morphine in the modulation of the response to noxious pressure on inflamed paws, using a supraspinally integrated test and various low doses of naloxone. Rats received an injection of carrageenin into the right hindpaw which resulted in an ipsilateral inflammatory response and decreased threshold to noxious pressure. Four hours post-carrageenin, the injection of 1 mg/kg i.v. morphine induced a significantly enhanced antinociceptive effect on the inflamed compared to the non-inflamed paws. Intrapantar injection of extremely low doses of naloxone (0.5 and 1 micrograms in a volume of 0.1 ml) significantly reduced this effect (naloxone being more effective when administered at the same time as morphine, compared to 15 min later), while equal doses of naloxone given systemically were inactive. These data confirm that synergism of peripheral and central actions may result in the augmented analgesic potency of morphine in rats subjected to inflammatory conditions. In addition, they provide further evidence for the complexity of opioid actions in inflammatory processes. In particular, the results are in line with the hypothesis that the paradoxical antinociceptive effect of extremely low doses of i.v. naloxone described in several studies is due to a central action.