Synergistic efficacy of tramadol and meloxicam on alleviation of pain and selected immunological variables after sciatic nerve ligation in rats

Sigma-1 receptor antagonist (BD-1063) potentiates the antinociceptive effect of quercetin in neuropathic pain induced by chronic constriction injury

Neuropathic pain is characterized by the presence of hyperalgesia and allodynia. Pharmacological treatments include the use of antiepileptics such as pregabalin or gabapentin, as well as antidepressants; however, given the role of the sigma-1 receptor in the generation and maintenance of pain, it has been suggested that sigma-1 receptor antagonists may be effective. There are also other alternatives that have been explored, such as the use of flavonoids such as quercetin. Due to the relevance of drug combinations in therapeutics, the objective of this work was to evaluate the effect of the combination of BD-1063 with quercetin in a chronic sciatic nerve constriction model using the "Surface of Synergistic Interaction" analysis method. The combination had preferable additive or synergistic effects, with BD-1063 (17.8 mg/kg) + QUER (5.6 mg/kg) showing the best antinociceptive effects. The required doses were also lower than those used individually to obtain the same level of effect. Our results provide the first evidence that the combination of a sigma-1 receptor antagonist and the flavonoid quercetin may be useful in the treatment of nociceptive behaviors associated with neuropathic pain, suggesting a new therapeutic alternative for this type of pain.

Evaluation of chemical restraint, isoflurane anesthesia and methadone or tramadol as preventive analgesia in spotted pacas (Cuniculus paca) subjected to laparoscopy

OBJECTIVE

To evaluate the efficacy and cardiopulmonary effects of ketamine-midazolam for chemical restraint, isoflurane anesthesia and tramadol or methadone as preventive analgesia in spotted pacas subjected to laparoscopy.

STUDY DESIGN

Prospective placebo-controlled blinded trial.

ANIMALS

A total of eight captive female Cuniculus paca weighing 9.3 ± 0.9 kg.

METHODS

Animals were anesthetized on three occasions with 15 day intervals. Manually restrained animals were administered midazolam (0.5 mg kg^-1) and ketamine (25 mg kg^-1) intramuscularly. Anesthesia was induced and maintained with isoflurane 30 minutes later. Tramadol (5 mg kg^-1), methadone (0.5 mg kg^-1) or saline (0.05 mL kg^-1) were administered intramuscularly 15 minutes prior to laparoscopy. Heart rate (HR), respiratory rate, mean arterial pressure (MAP), peripheral oxygen saturation (SpO₂), end-tidal CO₂ partial pressure (Pe'CO₂), end-tidal concentration of isoflurane (Fe'Iso), pH, PaO₂, PaCO₂, bicarbonate (HCO₃^-), anion gap (AG) and base excess (BE) were monitored after chemical restraint, anesthesia induction and at different laparoscopy stages. Postoperative pain was assessed by visual analog scale (VAS) for 24 hours. Variables were compared using anova or Friedman test (p < 0.05).

RESULTS

Chemical restraint was effective in 92% of animals. Isoflurane anesthesia was effective; however, HR, MAP, pH and AG decreased, whereas Pe'CO₂, PaO₂, PaCO₂, HCO₃^- and BE increased. MAP was stable with tramadol and methadone treatments; HR, Fe'Iso and postoperative VAS decreased. VAS was lower for a longer time with methadone treatment; SpO₂ and AG decreased, whereas Pe'CO₂, PaCO₂ and HCO₃^- increased.

CONCLUSIONS AND CLINICAL RELEVANCE

Ketamine-midazolam provided satisfactory restraint. Isoflurane anesthesia for laparoscopy was effective but resulted in hypotension and respiratory acidosis. Tramadol and methadone reduced isoflurane requirements, provided postoperative analgesia and caused hypercapnia, with methadone causing severe respiratory depression. Thus, the anesthetic protocol is adequate for laparoscopy in Cuniculus paca; however, methadone should be avoided.

Synergistic symptom-specific effects of ketorolac-tramadol and ketorolac-pregabalin in a rat model of peripheral neuropathy

BACKGROUND

Although current neuropathic pain treatment guidelines do not recommend the use of nonsteroidal anti-inflammatory drugs (NSAIDs), whether NSAIDs can serve as a useful adjuvant to conventional multimodal therapy remains unclear.

METHODS

The spared nerve injury (SNI) rats rapidly developed profound and long-lasting spontaneous and evoked pain behaviors, including mechanical and cold allodynia of the ipsilateral hind paw. At day 5, we first characterized the nociceptive responses to ketorolac, tramadol, pregabalin, and their combinations.

RESULTS

We found that tramadol and pregabalin exerted dose-dependent analgesic effects on both spontaneous and evoked behaviors. However, ketorolac alone did not suppress any behaviors regardless of the dose. Ketorolac-tramadol and ketorolac-pregabalin produced variable degrees of additive suppression of spontaneous and evoked behavioral responses. Cold allodynia was profoundly diminished after ketorolac was added to ineffective pregabalin or tramadol. Mechanical allodynia was markedly attenuated by ketorolac-pregabalin but less so by ketorolac-tramadol mixtures.

CONCLUSION

Our data demonstrated that an NSAID alone failed to relieve spontaneous or evoked pain behaviors in the rat SNI model, but when combined with a weak opioid and α-2-δ-ligand produced a profound synergistic analgesic effect on cold allodynia and discrepant efficacy for mechanical allodynia and spontaneous pain.

Synergistic interaction between tapentadol and flupirtine in the rat orafacial formalin test

Combination therapy with two or more analgesics is widely used for conditions associated with moderate to severe pain. Combinations of diverse analgesics with different modes of action can improve the risk-benefit ratio of analgesic treatments. The aim of this study is to evaluate the antinociceptive effect of tapentadol (TAP) and flupirtine (FLP), when administered separately or in combination, as well as their synergistic interaction in the orofacial formalin test in rats. After i.p. injection of TAP at different doses (2, 5, 10 and 15mg/kg), the biphasic nociceptive behavior was reduced in a dose-dependent manner in both phase I and II. Conversely, i.p. injection of FLP at different doses (0.6, 1.6, 3.3, 6.6, 16.6 and 22.2mg/kg) induced a dose-dependent antinociceptive effect in phase II only. TAP was found to be more effective than FLP. The interaction between TAP and FLP was synergistic in phase II with an interaction index (γ) of 0.50±0.24. The data reported in this study indicate that FLP enhances the antinociceptive effect of TAP and this drug combination might be potentially useful in the treatment of chronic pain.