Local infiltration of tramadol as an effective strategy to reduce post-operative pain: a systematic review protocol and meta-analysis.

OBJECTIVE: The purpose of this review is to evaluate the use and effectiveness of the local administration of tramadol in reducing post-operative pain during surgical interventions. METHODS: The PubMed, EMBASE and Cochrane Central Register of Controlled Trials (CENTRAL) databases will be searched for this review. This systematic review will include studies evaluating the clinical efficacy of the local infiltration of tramadol, with no study design restrictions. Only studies that present clear descriptions of local tramadol administration are published in peer-reviewed journals in the English, Italian, Spanish, French, Portuguese or German language and are published in full will be taken into consideration. A meta-analysis will be performed when there is sufficient clinical homogeneity among the retrieved studies, and only randomized controlled studies and quasi-randomized controlled studies will be included. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach will be used to assess the certainty in the evidence. If a quantitative analysis cannot be conducted, a qualitative description of the results of the retrieved studies will be provided. RESULTS: A high-quality synthesis of the current evidence on the local administration of tramadol for managing post-surgical pain will be illustrated using subjective reports and objective measures of performance. The primary outcomes will include the magnitude of post-operative pain intensity improvement, with improvement being as defined by a reduction by at least 2 points in the visual analogue scale (VAS) score or numerical rating scale (NRS) score. The secondary outcomes will be the magnitude of reduction in tramadol rescue doses and in other analgesic drug doses. CONCLUSION: This protocol will present evidence on the efficacy of tramadol in relieving post-surgical pain. SYSTEMIC REVIEW REGISTRATION: PROSPERO CRD42018087381.

Neuropathic pain and the endocannabinoid system in the dorsal raphe: pharmacological treatment and interactions with the serotonergic system.

We used a model of neuropathic pain consisting of rats with chronic constriction injury (CCI) of the sciatic nerve, in order to investigate whether endocannabinoid levels are altered in the dorsal raphe (DR) and to assess the effect of repeated treatment with (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate, a synthetic cannabinoid agonist, or N-(4-hydroxyphenyl)-5Z,8Z,11Z,14Z-eicosatetraenamide (AM404), an inhibitor of endocannabinoid reuptake, on DR serotonergic neuronal activity and on behavioural hyperalgesia. CCI resulted in significantly elevated anandamide but not 2-arachidonoylglycerol levels in the DR. Furthermore, as well as thermal and mechanical hyperalgesia, CCI caused serotonergic hyperactivity (as shown by the increase of basal activity of serotonergic neurones, extracellular serotonin levels and expression of 5-HT1A receptor gene). Repeated treatment with either (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate or AM404 reverted the hyperalgesia and enhanced serotonergic activity induced by CCI in a way attenuated by N-piperidino-5-(4-chlorophenyl)-1-(2,4dichlorophenyl)-4-methyl-3-pyrazolecarboxamide, a selective cannabinoid subtype 1 (CB1) receptor antagonist. Despite the elevated levels of anandamide following CCI, N-piperidino-5-(4-chlorophenyl)-1-(2,4dichlorophenyl)-4-methyl-3-pyrazolecarboxamide did not produce hyperalgesia or any other effect on serotonergic neuronal activity when administered alone. Furthermore, the effects of AM404 were not accompanied by an increase in endocannabinoid levels in the DR. In conclusion, following CCI of the sciatic nerve, the endocannabinoid and serotonergic systems are activated in the DR, where repeated stimulation of CB1 receptors with exogenous compounds restores DR serotonergic activity, as well as thermal and mechanical nociceptive thresholds, to pre-surgery levels. However, an elevated level of endogenous anandamide in the DR does not necessarily contribute to the CB1-mediated tonic control of analgesia and serotonergic neuronal activity.