Evaluation of the efficacy of intrathecal injection of amitriptyline and doxepin in spinal anesthesia in comparison with bupivacaine in rats

The Effect of Intrathecal Injection of Dextromethorphan on the Experimental Neuropathic Pain Model

Background

Peripheral glucocorticoid receptors (GRs) are altered by peripheral nerve injury and may modulate the development of neuropathic pain. Two central pathogenic mechanisms underlying neuropathic pain are neuroinflammation and N-methyl-D-aspartate receptor (NMDAR)-dependent neural plasticity in the spinal cord.

Objectives

This study examined the effect of the non-competitive NMDAR antagonist dextromethorphan on partial sciatic nerve ligation (PSL)-induced neuropathic pain and the spinal expression of the glucocorticoid receptor (GR).

Methods

Male mice were randomly assigned into a sham group and two groups receiving PSL followed by intrathecal saline vehicle or dextromethorphan (iDMP). Vehicle or iDMP was administered 8 - 14 days after PSL. The hotplate paw-withdrawal latency was considered to measure thermal pain sensitivity. The spinal cord was then sectioned and immunostained for GR.

Results

Thermal hyperalgesia developed similarly in the vehicle and iDMP groups prior to the injections (P = 0.828 and 0.643); however, it was completely mitigated during the iDMP treatment (P < 0.001). GR expression was significantly higher in the vehicle group (55.64 ± 4.50) than in the other groups (P < 0.001). The iDMP group (9.99 ± 0.66) showed significantly higher GR expression than the sham group (6.30 ± 1.96) (P = 0.043).

Conclusions

The suppression of PLS-induced thermal hyperalgesia by iDMP is associated with the downregulation of GR in the spinal cord, suggesting that this analgesic effect is mediated by inhibiting GR-regulated neuroinflammation.

The Analgesic Efficacy of Intrathecal Bupivacaine and Fentanyl with Added Neostigmine or Magnesium Sulphate

Background

An appropriate anesthesia duration with minimal side effects and prolonged postoperative analgesia are the ideal characteristics of an intrathecal drug used during spinal anesthesia. Neostigmine and magnesium sulphate have been used as spinal anesthetic additives with narcotics and local anesthetics.

Objectives

This study aimed to assess the analgesic properties of intrathecal neostigmine and magnesium sulphate by adding them to intrathecal bupivacaine-fentanyl.

Methods

: In total, 210 patients undergoing tibial fracture surgery were enrolled in a double-blinded clinical trial study. Patients were randomly allocated to one of three groups: group F received 10 mg of bupivacaine and 25 µg of fentanyl as intrathecal drug for spinal anesthesia, group N received 150 µg of neostigmine added to 10 mg of bupivacaine and 25 µg of fentanyl, and group M received 50 mg of magnesium sulphate added to 10 mg of bupivacaine and 25 µg of fentanyl. Analgesia duration, motor blockade scores, postoperative pain scores 6 and 12 hours after surgery, postoperative voiding time, and the incidence of hypotension, bradycardia, respiratory depression, and nausea and vomiting were recorded.

Results

Group M showed significantly longer analgesia duration (330.76 ± 80.98 minutes) than group F (280.98 ± 60.33 minutes). The pain scores in group M 6 hours (NRS: 2.44 ± 0.98) and 12 hours (NRS: 4.10 ± 0.88) after surgery were significantly lower than those of the other two groups. Before discharge from recovery, motor blockade scores and voiding time were not significantly different between the three groups. Hypotension (40%), bradycardia (25%), and nausea and vomiting (70%) were more obvious among group N patients. Respiratory depression did not occur in any patients.

Conclusions

The addition of 50 mg of magnesium sulfate to a bupivacaine–fentanyl solution for intrathecal anesthesia improved the efficacy and duration of the analgesia without any significant side effects. The addition of 150 µg of neostigmine increased the incidence of hypotension, bradycardia, and nausea and vomiting. Moreover, neostigmine failed to prolong analgesia duration.

Bupivacaine effectively relieves inflammation-induced pain by suppressing activation of the NF-κB signalling pathway and inhibiting the activation of spinal microglia and astrocytes

The pain induced by local acute inflammation results in mild to severe discomfort, in addition to the possibility of physiological dysfunction and psychiatric disorders, such as sleep disorders and depression. However, the pathogenesis of pain is yet to be fully elucidated. In the present study, the effects of bupivacaine were explored in rat models inflammatory pain in order to investigate the anti-pain mechanism of bupivacaine. Complete Freund's adjuvant (CFA) was injected into the right rear foot of the rats to establish a model of transient inflammation-induced pain. Rats were randomly divided into four groups (n=8): CFA, CFA plus bupivacaine, CFA plus saline and untreated. The mechanical withdrawal threshold (MWT) of the rats was detected prior to and following CFA injection, and the results demonstrated that the MWT in the right rear foot significantly decreased from the 1st day of CFA injection (P<0.01; n=8), as compared with the untreated controls. Bupivacaine treatment was demonstrated to significantly increase the MWT of rats treated with CFA stimulation, as compared with the CFA group (P<0.01). Rotarod testing was performed to assess the motor activity of the rats, and the results demonstrated no significant differences among the four groups (P>0.05). Furthermore, the respective body weights of the rats were determined every two days before and after CFA injection, and no significant differences were detected among the four groups (P>0.05). Western blot analysis was performed to analyze expression levels of IκB and nuclear factor (NF)-κB, and the results demonstrated that bupivacaine increased the expression of IκB and decreased the expression levels of NF-κB, as compared with the rats with CFA-induced inflammatory responses, suggesting that bupivacaine inhibited NF-κB activation in the dorsal horn of the lumbar spinal cord of the model rats. Furthermore, reverse transcription-quantitative polymerase chain reaction analysis was performed to analyze the expression levels of inflammatory cytokines, which demonstrated that bupivacaine significantly inhibited the expression of TNF-α, IL-1β and IL-6, as compared with the untreated group (P<0.01). Moreover, bupivacaine treatment significantly decreased the expression of spinal microglial marker OX42 and astrocyte marker-glial fibrillary acidic protein, as compared with the rats in the CFA group (P<0.01). The present findings demonstrated that treatment with bupivacaine significantly decreased the activation of microglia and astrocytes in rat models of inflammatory pain. Therefore, the present results may provide clarification of the pathogenesis and mechanism of inflammation-induced pain and may provide novel therapeutic strategies for the clinical treatment of pain.

B. S, Pandarpurkar S, Jajee P. Intrathecal Midazolam as an Adjuvant in Pregnancy-Induced Hypertensive Patients Undergoing an Elective Caesarean Section: A Clinical Comparative Study

Background

A pain-free postoperative period is essential following a caesarean section so new mothers may care for and bond with their neonates. Intrathecal adjuvants are often administered during this procedure to provide significant analgesia, but they may also have bothersome side effects. Intrathecal midazolam produces effective postoperative analgesia with no significant side effects.

Objectives

This prospective, randomized, double-blind study was designed to compare the analgesic efficacy and safety of intrathecal midazolam vs. plain bupivacaine as an adjunct to bupivacaine in pregnancy-induced hypertension patients scheduled for elective caesarean section.

Methods

Sixty patients diagnosed with pregnancy-induced hypertension on regular treatment who were scheduled for a caesarean section were randomly allocated into two groups: a control group (Group BC, n = 30) and a midazolam group (Group BM, n = 30). Both groups received 10 mg (2 mL) of 0.5% hyperbaric bupivacaine. Group BC received 0.4 mL of distilled water, while group BM received 0.4 mL (2 mg) of midazolam intrathecally. The duration of postoperative analgesia, analgesic requirements during the first 24 hours after surgery, onset times and durations of sensory and motor blocks, incidence of hypotension, vasopressor requirements, and side effects were recorded.

Results

Postoperative analgesia was significantly longer in the midazolam group compared to the control group (201.5 minutes vs. 357.6 minutes). The mean onset times of the sensory and motor blocks were significantly faster (P < 0.01) in the midazolam group compared to the control group. The mean times to attain the maximum sensory level and motor blocks were also significantly faster in the midazolam group compared to the control group (P < 0.05). The incidence of hypotension was 6.6% in the midazolam group and 36.6% in the control group, which was highly significant. In addition, the number of patients with side effects was significantly lower in the midazolam group compared to the control group.

Conclusions

Intrathecal midazolam 2 mg provides significantly longer and effective postoperative analgesia with no side effects.