Intrathecal clonidine and bupivacaine have synergistic analgesia for acute thermally or inflammatory-induced pain in rats

Effects of fadolmidine, an α2 -adrenoceptor agonist, as an adjuvant to spinal bupivacaine on antinociception and motor function in rats and dogs

α2 -Adrenoceptor agonists such as clonidine and dexmedetomidine are used as adjuvants to local anesthetics in regional anesthesia. Fadolmidine is an α2 -adrenoceptor agonist developed especially as a spinal analgesic. The current studies investigate the effects of intrathecally administered fadolmidine with a local anesthetic, bupivacaine, on antinociception and motor block in conscious rats and dogs. The antinociceptive effects of intrathecal fadolmidine and bupivacaine alone or in combination were tested in the rat tail-flick and the dog's skin twitch models. The durations of motor block in rats and in dogs were also assessed. In addition, the effects on sedation, mean arterial blood pressure, heart rate, respiratory rate and body temperature were evaluated in telemetrized dogs. Concentrations of fadolmidine in plasma and spinal cord were determined after intrathecal and intravenous administration in rats. Co-administration of intrathecal fadolmidine with bupivacaine increased the magnitude and duration of the antinociceptive effects and prolonged motor block without hypotension. The interaction of the antinociceptive effect was synergistic in its nature in rats. Concentration of fadolmidine in plasma was very low after intrathecal dosing. Taken together, these studies show that fadolmidine as an adjuvant to intrathecal bupivacaine provides enhanced sensory-motor block and enables a reduction of the doses of both drugs. The results indicate that co-administration of fadolmidine with intrathecal bupivacaine was able to achieve an enhanced antinociceptive effect without hypotension and could thus represent a suitable combination for spinal anesthesia.

Regulation of murine arthritis by systemic, spinal, and intra-articular adrenoceptors

BACKGROUND

The regulation of the immune system by the sympathetic nervous system is allowing the design of novel treatments for inflammatory disorders such as arthritis. In this study, we have analyzed the effects of α- and β-adrenoceptor agonists injected subcutaneously, intrathecally, or intra-articularly in zymosan-induced arthritis.

METHODS

Murine arthritis was induced by intra-articular (knee joint) injection of zymosan. α1 (phenylephrine), α2 (clonidine), β1 (dobutamine), or β2 (salbutamol)-adrenoceptor agonists were injected subcutaneously (sc), intrathecally (it), or intra-articularly (ia) to activate peripheral, spinal, or intra-articular adrenoceptors and to study their effects on articular edema formation and neutrophil migration into the synovial cavity.

RESULTS

Treatments with phenylephrine did not affect the edema formation, but it increased neutrophil migration when injected subcutaneously (155.3%) or intra-articularly (187.7%). Treatments with clonidine inhibited neutrophil migration (59.9% sc, 68.7% it, 42.8% ia) regardless of the route of administration, but it inhibited edema formation only when injected intrathecally (66.7%) or intra-articularly (36%) but not subcutaneously. Treatments with dobutamine inhibited both edema (42.0% sc, 69.5% it, 61.6% ia) and neutrophil migration (28.4% sc, 70.3% it, 82.4% ia) in a concentration dependent manner. Likewise, all the treatments with salbutamol also inhibited edema formation (89.9% sc, 62.4% it, 69.8% ia) and neutrophil migration (76.6% sc, 39.1% it, 71.7% ia).

CONCLUSION

Whereas the β-adrenoceptor agonists induced anti-inflammatory effects regardless of their route of administration, α1- and α2-adrenoceptor agonists induced either pro- and anti-inflammatory effects, respectively.

Effect of clonidine on the cutaneous silent period during spinal anesthesia

AIM

To investigate the effect of clonidine on the cutaneous silent period (CSP) during spinal anesthesia.

METHODS

A total of 67 adult patients were included in this randomized, prospective, single-center, double-blind trial. They did not have neurological disorders and were scheduled for inguinal hernia repair surgery. This trial was registered on ClinicalTrials.gov (NTC03121261). The patients were randomized into two groups with regards to the intrathecally administered solution: (1) 15 mg of 0.5% levobupivacaine with 50 µg of 0.015% clonidine, or (2) 15 mg of 0.5% levobupivacaine alone. There were 34 patients in the levobupivacaine-clonidine (LC) group and 33 patients in the levobupivacaine (L) group. CSP and its latency were measured four times: prior to the subarachnoid block (SAB), after motor block regression to the 0 level of the Bromage scale, with ongoing sensory blockade, and both 6 and 24 h after SAB.

RESULTS

Only data from 30 patients in each group were analyzed. There were no significant differences between the groups investigated preoperatively and after 24 h. The CSP of the L group at the time point when the Bromage scale was 0 was 44.8 ± 8.1 ms, while in the LC group it measured 40.2 ± 3.8 ms (P = 0.007). The latency in the L group at the time point when the Bromage scale was 0 was 130.3 ± 10.2 ms, and in the LC group it was 144.7 ± 8.3 ms (P < 0.001). The CSP of the L group after 6 h was 59.6 ± 9.8 ms, while in the LC group it was 44.5 ± 5.0 ms (P < 0.001). The latency in the L group after 6 h was 110.4 ± 10.6 ms, while in LC group it was 132.3 ± 9.7 ms (P < 0.001).

CONCLUSION

Intrathecal addition of clonidine to levobupivacaine for SAB in comparison with levobupivacaine alone results in a diminished inhibitory tonus and shortened CSP.

Postoperative Analgesia After Panhysterectomy, Addition of Clonidine to Bupivacaine: Boon for the Patients

INTRODUCTION

Postoperative period after panhysterectomy is very painful as there is too much tissue handling. In the practice of regional anesthesia neuraxial, opioids have been used extensively as an adjuvant to bupivacaine to enhance the potency and duration of sensory and motor block produced by bupivacaine with satisfactory results. However, delayed respiratory depression by opioids has prompted further research to develop nonopioid analgesics. This study was undertaken to assess the degree of sensory and motor block and postoperative analgesia provided by low dose 50 μg intrathecal clonidine admixed with 0.5% hyperbaric bupivacaine as compared to bupivacaine alone in patients undergoing a total abdominal hysterectomy.

MATERIALS AND METHODS

Hundred adult patients of American Society of Anesthesiologist Class 1 and 2 were randomly allocated to Group A and Group B. Group A patients received 15 mg 0.5% hyperbaric bupivacaine with 50 μg clonidine intrathecally. Group B patients received 15 mg 0.5% hyperbaric bupivacaine with normal saline.

OBSERVATION AND RESULTS

The mean duration of motor block was significantly higher in Group A (270.80± 66.0 min) as compared to Group B (184.60 ± 72.03 min), with statistically significant difference. There was also statistically significant difference in the duration of sensory block between Group A (290.20 ± 80.27 min) and Group B (190.83 ± 86.90 min). The duration of postoperative analgesia was significantly higher in Group A as compared to Group B (541.06 ± 130.64 min and 252.80 ± 84.10 min respectively).

CONCLUSION

Addition of intrathecal clonidine 50 μg to bupivacaine (15 mg, 0.5%) prolongs the duration of sensory and motor block and duration of analgesia, thus produces an effective spinal anesthesia and good postoperative analgesia for longer duration and reduced postoperative analgesic requirement.

Role of Clonidine as adjuvant to intrathecal bupivacaine in patients undergoing lower abdominal surgery: A randomized control study

Background:

Neuraxial anesthesia greatly expands the anesthesiologist armamentarium, providing alternatives to general anesthesia, especially in the lower abdominal surgeries. Clonidine, an alpha-2 adrenergic agonist, has a variety of actions, including potentiation of effects of local anesthetics. This study was undertaken to assess the degree of sensory and motor block and postoperative analgesia provided by low dose (50 mcg) intrathecal clonidine admixed with bupivacaine.

Aims:

The aim of this study is to establish efficacy and safety of intrathecal clonidine as adjuvant to bupivacaine.

Settings and Design:

The type of the study was double-blind randomized trial.

Materials and Methods:

Hundred patients were randomly allocated in two groups, A and B. Group A received bupivacaine 0.5%, 3 ml with placebo (normal saline 0.33 ml) and Group B, bupivacaine 0.5%, 3 ml with clonidine 50 μg (0.33 ml).

Statistical Analysis Used:

Statistical Package for Social Sciences version 15.0 statistical analysis software.

Results:

Mean duration of motor block was significantly higher in Group B (280.80 ± 66.88 min) as compared with Group A (183.60 ± 77.06 min). Significant difference in duration of sensory block was noted between Group B (295.20 ± 81.17 min) and Group A (190.80 ± 86.94 min). Duration of postoperative analgesia was significantly higher in Group B as compared to Group A (551.06 ± 133.64 min and 254.80 ± 84.19 min respectively). Mean visual analog scale scores at different time intervals were significantly lower in the study group (except for 4-h time interval), but the control group had better hemodynamic stability as compared with study group.

Conclusion:

The findings in this study suggested that use of clonidine 50 μg added to bupivacaine for spinal anesthesia effectively increased the duration of sensory block, duration of motor block, and duration of analgesia.

Analgesic and sympatholytic effects of low-dose intrathecal clonidine compared with bupivacaine: a dose-response study in female volunteers

BACKGROUND

A wide range of doses has been suggested for intrathecal clonidine, but no dose-ranging study has examined analgesic effects below 100 µg. The primary aim of this volunteer study was to assess the dose vs analgesic effect relationship for doses of intrathecal clonidine below 100 µg.

METHODS

After IRB approval and signed informed consent, 11 healthy female volunteers participated in this randomized, double-blinded, cross-over study using a dose-ranging sparse-sampling technique. Participants received intrathecal clonidine (doses 0-100 µg; n=10) and intrathecal bupivacaine (doses 0-8.8 mg; n=9) on separate study days. At baseline, 30, and 60 min from drug administration, experimental heat pain tolerance was assessed at both a lumbar and a cranial dermatome. Heat and cold perception thresholds were assessed at the same time intervals. Heart rate (HR), arterial pressure, and forearm-finger and toe-leg cutaneous temperature gradients (Tfinger-arm and Ttoe-leg) were used as measures of sympatholysis.

RESULTS

Both intrathecal clonidine and bupivacaine caused significant, dose-dependent analgesic effects at the leg but not the head. Significant analgesia to experimental heat pain was detected above 25 µg clonidine and 3 mg bupivacaine. Administration of bupivacaine but not clonidine resulted in a significant dose-related decrease in HR and Ttoe-leg; neither drug caused dose-related sympatholytic effects in the doses used.

CONCLUSIONS

After 50 µg clonidine or 5 mg bupivacaine, the heat pain tolerance increased by ∼1°C, similar to the analgesic effect of 5 mg epidural morphine or 30 µg epidural fentanyl in previous studies using this experimental heat pain model. Our results provide additional data for rational dose selection of intrathecal clonidine.

Antinociceptive synergy between the cannabinoid receptor agonist WIN 55,212-2 and bupivacaine in the rat formalin test

BACKGROUND

The analgesic interaction between cannabinoids and local anesthetics has not been investigated. We sought to determine the nature of the interaction between the intrathecal cannabinoid receptor agonist (WIN 55,212-2) and bupivacaine using the formalin test.

METHODS

Lumbar intrathecal catheters were implanted in male Sprague-Dawley rats. After intrathecal administration of WIN 55,212-2, bupivacaine, or their combination, 50 microL of 5% formalin was injected subcutaneously into the hindpaw. Dose-response curves were established and the respective ED50 (50% effective dose) values were determined for each agent alone. Fixed-ratio combinations of WIN 55,212-2 and bupivacaine were tested for combined antinociceptive effects in the formalin test and an isobolographic analysis was performed to characterize the pharmacologic interaction of both drugs.

RESULTS

Intrathecally administered WIN 55,212-2, bupivacaine, or their combination produced a dose-dependent decrease in the number of flinches during Phase 1 and 2 of the formalin test. Isobolographic analysis revealed a synergistic interaction between intrathecal WIN 55,212-2 and bupivacaine in both phases of the formalin test. In combination, the ED50 value was significantly smaller than the theoretical additive value (P < 0.05).

CONCLUSIONS

These results demonstrate that intrathecally coadministered WIN 55,212-2 and bupivacaine provide synergistic antinociceptive interaction in both phases of the formalin test.

Dexmedetomidine prolongs spinal anaesthesia induced by levobupivacaine 0.5% in guinea-pigs

Alpha-2 adrenoceptor agonists have been used in association with local anaesthetic to increase the duration of spinal anaesthesia. Intrathecal administration of clonidine prolonged motor blockade induced by local anaesthetic. Since the affinity of dexmedetomidine (DEX) to alpha-2 adrenoceptors is eight-times greater than clonidine, it is expected that DEX could be advantageous in clinical anaesthesia. We investigated the duration of motor nerve block induced by spinal injection of 0.5% levobupivacaine (LVB) associated with intrathecal or intraperitoneal administration of DEX. Seventy-two guinea-pigs were randomly divided in 12 groups, which were all treated with intrathecal injection of 50 microL of LVB. DEX was injected intrathecally with LVB in 6 groups or injected intraperitoneally after LVB in another 6 groups. Intrathecal DEX (0.1, 0.2 and 0.4 microg) increased the LVB-induced motor anaesthesia from 48 (41-66) min to 84.5 (52-91) min (P < 0.05), 101.5 (83-115) min (P < 0.05) and 105 (97-114) min (P < 0.05), respectively. Similarly, intraperitoneal DEX (20 and 40 microg kg(-1)) increased the motor blockade from 48.5 (33-59) min to 88 (71-114) min (P < 0.05) and 114.5 (103-156) min (P < 0.05), respectively. Pre-treatment with yohimbine reduced the duration of motor block from 101.5 (83-115) to 76.5 (68-86) min (P < 0.05) or from 114.5 (103-156) to 90 (83-93) min (P < 0.05) when DEX was administered by the intrathecal or intraperitoneal routes. Motor block induced by spinal injection of LVB was prolonged by intrathecal and systemic administration of DEX, which was partially dependent on activation of alpha-2 adrenoceptors.

Effects of a 5-HT2A receptor antagonist, sarpogrelate on thermal or inflammatory pain

The effects of intrathecally and systemically administered 5-hydroxytriptamine (5-HT)(2A) receptor antagonist, sarpogrelate on acute thermal or formalin induced pain were examined. Male Sprague-Dawley rats with lumbar intrathecal catheters were tested with their tail withdrawal response to thermal stimulation (tail flick test) or their paw flinching and shaking response by subcutaneous formalin injection into the hind paw (formalin test) after intrathecal or intraperitoneal administration of sarpogrelate. 5-HT(2A) receptor agonist was used to antagonize the effects of sarpogrelate. In the tail flick test, only intraperitoneal administration induced analgesia. In the formalin test, both intrathecal and intraperitoneal administration were analgesic. The analgesic effects were inhibited by pretreatment with 5-HT(2A) receptor agonist. Motor disturbance and behavioral side effects were not observed. In conclusion, sarpogrelate might be analgesic on inflammatory induced acute and facilitated pain by intrathecal or systemic administration. However, only systemic administration could be effective on thermal induced acute pain.