Co-analgesics for neuropathic pain in the rat model of spared nerve injury

DEAR EDITOR,

Neuropathic pain is difficult to diagnose and manage.¹ In the past, NSAID was deemed useless in treating neuropathic pain. But in the article entitled “Synergistic symptom-specific effects of ketorolac-tramadol and ketorolac-pregabalin in a rat model of peripheral neuropathy,”² the authors reported that combining NSAID with a weak opioid and α-2-δ-ligand had produced a profound synergistic analgesic effect for the neuropathic pain. Results provided a new implication for the clinical management of neuropathic pain. Their findings, however, can be modified, at least in part, to be more robust. First, to quantify the stimulation sensitivity, the baseline behavior could have been evaluated before the nerve ligation and those rats exhibiting reduced motor behaviors should be excluded from study. Second, to select appropriate subjects for the study, it was necessary to distinguish between experimental rats that had either well-developed or poorly developed neuropathic pain.³ Because in the rat model of spared nerve injury, pain could have been induced by various factors, and different observation times post ligation could be related to different injury statuses.⁴ Third, other researchers⁵ used the placebo group to exclude incidental effects caused by incision trauma or anesthetic agents. Such placebo group could help determining the true effects. Fourth, to mimic the clinical scenario of managing the neuropathic pain, the study analgesic drugs should be injected only after the development of neuropathic pain had been confirmed postoperatively.⁶ These technical modifications of the experiment can provide more confidence in using NSAIDs to treat neuropathic pain.