Novel strategy for the control of postoperative pain: long-lasting effect of an implanted analgesic hydrogel in a rat model of postoperative pain

Local anesthetic delivery systems for the management of postoperative pain

Postoperative pain (POP) is a major clinical challenge. Local anesthetics (LAs), including amide-type LAs, ester-type LAs, and other potential ion-channel blockers, are emerging as drugs for POP management because of their effectiveness and affordability. However, LAs typically exhibit short durations of action and prolonging the duration by increasing their dosage or concentration may increase the risk of motor block or systemic local anesthetic toxicity. In addition, techniques using LAs, such as intrathecal infusion, require professional operation and are prone to catheter displacement, dislodgement, infection, and nerve damage. With the development of materials science and nanotechnology, various LAs delivery systems have been developed to compensate for these disadvantages. Numerous delivery systems have been designed to continuously release a safe dose in a single administration to ensure minimal systemic toxicity and prolong pain relief. LAs delivery systems can also be designed to control the duration and intensity of analgesia according to changes in the external trigger conditions, achieve on-demand analgesia, and significantly improve pain relief and patient satisfaction. In this review, we summarize POP pathways, animal models and methods for POP testing, and highlight LAs delivery systems for POP management. STATEMENT OF SIGNIFICANCE: Postoperative pain (POP) is a major clinical challenge. Local anesthetics (LAs) are emerging as drugs for POP management because of their effectiveness and affordability. However, they exhibit short durations and toxicity. Various LAs delivery systems have been developed to compensate for these disadvantages. They have been designed to continuously release a safe dose in a single administration to ensure minimal toxicity and prolong pain relief. LAs delivery systems can also be designed to control the duration and intensity of analgesia to achieve on-demand analgesia, and significantly improve pain relief and patient satisfaction. In this paper, we summarize POP pathways, animal models, and methods for POP testing and highlight LAs delivery systems for POP management.

Long-lasting postoperative analgesia with local anesthetic-loaded hydrogels prevent tumor recurrence via enhancing CD8+T cell infiltration

Postoperative pain (POP) can promote tumor recurrence and reduce the cancer patient's quality of life. However, POP management has always been separated from tumor treatment in clinical practice, and traditional postoperative analgesia using opioids is still unsatisfactory for patients, which is not conducive to tumor treatment. Here, ropivacaine, a popular amide-type LA, was introduced into a Pluronic F127 hydrogel. Postoperative analgesia with ropivacaine-loaded hydrogels reduced the incidence of high-dose ropivacaine-induced convulsions and prolonged pain relief for more than 16 h. More interestingly, ropivacaine-loaded hydrogel was found to upregulate major histocompatibility complex class I (MHC-I) in tumor cells by impairing autophagy. Therefore, a hydrogel co-dopped with ropivacaine and TLR7 agonist imiquimod (PFRM) was rationally synthesized. After postoperative analgesia with PFRM, imiquimod primes tumor-specific CD8⁺T cells through promoting DCs maturation, and ropivacaine facilitates tumor cells recognition by primed CD8⁺T cells through upregulating MHC-I. Consequently, postoperative analgesia with PFRM maximumly increases CD8⁺T cells infiltration into residual tumor tissue and prevents tumor recurrence. Overall, this study for the first time provides an LA-based approach for simultaneous long-lasting postoperative analgesia and prevention of tumor recurrence.

The efficacy of Antipyretic Analgesics administration intravenously for Preventing Rocuronium-Associated Pain/Withdrawal Response: a systematic review and meta-analysis

Background

Rocuronium-associated injection pain/withdrawal response (RAIPWR) was non-ideal but occurred frequently when injection intravenously during anesthesia induction. Many studies had reported that pretreating with antipyretic analgesics (AAs) could reduce the occurrence of RAIPWR, but there was no consensus yet. Therefore, this meta-analysis was designed to systematically evaluate the benefits of AAs on RAIPWR in patients.

Methods

PubMed, Cochrane Library, Ovid, EMbase, Chinese National Knowledge Infrastructure (CNKI), Wan Fang Data were searched by January 1st 2019 for randomized controlled trials (RCTs) applying AAs to alleviate RAIPWR in patients who underwent elective surgery under general anesthesia. Two investigators assessed quality of RCTs and extracted data respectively and the meta-analysis was carried on Revman 5.3 software. Moreover, we compared AAs in pros and cons directly with lidocaine, the most reported medicine to prevent RAIPWR.

Results

Data were analyzed from 9 RCTs totaling 819 patients. The results of Meta-analysis showed that compared to the control group, pretreating with AAs could prevent the total occurrence of RAIPWR [Risk ratio (RR), 0.52; 95% confidence interval (CI), 0.42 to 0.66; P < 0.0001], and took effect on moderate (RR, 0.56; 95%CI, 0.43 to 0.73; P < 0.0001) and severe RAIPWR (RR = 0.14; 95%CI, 0.08 to 0.24; P < 0.00001). When compared to lidocaine, the preventive effect was not so excellent as the latter but injection pain induced by prophylactic occurred less.

Conclusion

The currently available evidence suggested that pretreating with AAs intravenously could alleviate RAIPWR.

Trial registration

PROSPERO CRD42019129776.

Analgesia in clinically relevant rodent models of sepsis

Postoperative analgesia in rodent sepsis models has been considerably neglected in the past. However, intentions to model clinical practice, increasing awareness of animal ethics, efforts to apply the 3Rs (replacement, reduction, refinement), and stricter legislation argue for a change in this respect. In this review, we describe different concepts of analgesia in rodent models of sepsis focusing on opioid agonists as well as non-opioid analgesics. Advantages and pitfalls in study design and side-effects are discussed. Score sheets should be used to adapt analgesia or to terminate experiments using humane endpoints. Further research is needed to differentiate behavioral changes caused by sepsis and pain or as a consequence of analgesia. Information on the efficacy of analgesia in sepsis models is scarce. Hence, studies are needed to identify the best ways to reduce suffering of research animals and thereby optimize the clinically relevant rodent models of sepsis.